Page 1 of 3 123 LastLast
Results 1 to 100 of 222
  1. #1
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    As my Powertap hub has died I've been trying to consider what may be a good replacement. The Power2Max MTB power meter looks like a possibility. One nice thing about it is that it uses an accelerometer for cadence so you don't need a cadence magnet attached to the frame for it to work.



    http://www.power2max.de/europe/en/Pr.../rotor-3d-mtb/

    DCRainmaker review of road version:

    http://www.dcrainmaker.com/2013/01/p...th-review.html

    Has anyone tried one and how does it hold up in bad weather? Riding in the UK getting soaked is unavoidable.

    For my bike I'd probably go for a Rotor 3D crank (alloy rather than carbon crank arms so can be welded and modified) in a triple chainset version with a 169mm q factor, allowing me to keep my current setup of 44/33/23 front chainrings.

    I have to use a modified left hand crank as I'm unable to use a normal length crank due to my knee not bending. I also use Rotor Q ring oval chainrings. Would a modified crank and oval rings result in inaccurate power readings?

    This picture shows my current modified crank, which is used with a Shimano Deore XT chainset. I'd have to get a new one made to match the Rotor cranks. It has a 75mm crank length and a 50mm swing crank. The right hand crank is a standard 175mm crank with no alterations.

    Swing crank explanation:
    http://www.highpath.net/highpath/cycles/swingcrank.html

    The swing crank allows you to pedal without bending your knee as much as normal.







    .

  2. #2
    mtbr member
    Reputation: serious's Avatar
    Join Date
    Jan 2005
    Posts
    3,201
    Wow, first time I see a swing crank. Very ingenious, I must add.
    My rides:
    Lynskey Ti Pro29 SL singlespeed
    KHS Team 29
    S-Works Roubaix SL3 Dura Ace
    KHS CX 550 cyclocross

  3. #3
    mtbr member
    Reputation:
    Join Date
    Oct 2005
    Posts
    2,683
    Paula Newby Fraser use to ride a set of funky cranks like does on her Triathlon bike..

  4. #4
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I've been doing a bit of reading up on Power2Max power meters. For the road versions you can buy just a seperate power meter spider and fit your own cranks and chainrings. The MTB versions appear to come fully assembled however.

    I found this quote:

    "I have a P2M on my road bike with Rotor 3D+ crank and O’Symetric chain rings. Works quite well although front shifting is a bit finicky. I’m contemplating getting a P2M for my MTB, but I want assymetric chain rings on that one as well. P2M told me all their MTB products only came with “pre-installed” chainrings as the power meter device (battery compartment?) was blocking access to (at least one of) the chainring bolts." Erik Wolla

    http://www.dcrainmaker.com/2013/08/p...atibility.html

    Ideally I want to use my own combination of chainrings (Rotor QRing 23T and 33T oval rings with a 44T round outer chainring.) I've emailed Power2Max to see if they can clarify this as it could be a lot of hassle if it's not possible to change chainrings without sending it back to the company.

    The other thing about Power2Max is that in order to buy direct from the European site they don't currently accept credit cards or Paypal. It seems that you have to pay by direct Bank Transfer instead.

    There are various German web shops, such as this one, where you can buy Power2Max with different payment methods but it does add a bit more complication.

    http://www.powermeter24.com/en/products/power2max

    This thread is a a bit long and rambling but has some relevant links and discussion about Power2Max:

    http://www.lfgss.com/thread98428.html

    Also:

    http://wellmt.wordpress.com/2013/05/...x-power-meter/

    .

  5. #5
    mtbr member
    Reputation: wetpaint's Avatar
    Join Date
    Sep 2009
    Posts
    313
    Have you contacted Stages to explain the situation and see if they can do a custom powermeter for you? It seems like they should be able to put the powermeter on the DS instead of NDS, that way you could keep your existing NDS crankarm

  6. #6
    mtbr member
    Reputation: CulBaire's Avatar
    Join Date
    Jan 2004
    Posts
    858
    Probably not much help but I've used the early road model for a few rides and found while yes it was good, it did what it was meant to it did have issues with tempreture change and recording a lower figure then the effort(s) would suggest. From what I understand this has been fixed by way of a firmware update and the later models are no longer suseptable to issues with tempreture change.


    Now the bit I might be able to help with, there is an NZ online shop that sells Power2max power meters, spiders, parts etc... I think they are the distributer in NZ but their pricing is quite competative and offer free shipping on orders over a set price (atleast to Aus), and you don't pay GST so it brings the price down (as does the US exchange rate).

    Power2max » Bikecycle
    Cul is a regretted trademark of the CulBaire Co'op Pty Ltd, as are his random ramblings and associated bullshit.

  7. #7
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    The problem with the Stages power meter is that it measures torque applied to just one crank arm. It then doubles that torque figure to estimate overall power output, using the assumption that power output is equal between both of your legs. Because my power output is so uneven and imbalanced between legs Stages would display either an extremely low power figure (measuring left leg) or an extremely high power figure (if it were measuring the right leg). In order for a power meter to work for me it has to record power somewhere in the drivetrain. Crank spider, which records power produced from both legs (eg: Power2Max, SRM, Quarq) or at the hub (Powertap). The pedal based power meters (eg: Polar, Garmin Vector) require equal length cranks on either side, ruling them out too.

    This diagram is from the DCRainmaker Stages review:



    "As you can see, the normal pedaling is pretty similar to each other. As I shift into Right-leg heavy (well beyond normal right-leg heavy), you see the Stages power meter (which is left-leg measured), drop significantly. Again, this is an exaggeration of an imbalance for the point of this graph, but it shows the impact. Then, as I shift to left-leg heavy, you see that it substantially increases the measured total power well above what was actually being put out (which was hard-set at 150w).

    Next, as I unclip the left leg entirely the power drops to zero. In fact, the cadence also dropped out (which surprised me). The cadence was normal for all other minutes of this test except the left-leg unclipped. As I went into left-leg only with right unclipped, you see the same near perfect doubling of actual power. And finally, as I return to normal power, you see the two stabilize on top of each other.

    Again, the point here is to simply illustrate the relationship between left/right, and the fact that the unit is measuring torque (bending) in the left-crank arm, and thus any power exerted from the right crank arm simply isn’t captured.

    Lastly, one item of note – when the unit measures power, it takes into account data from the accelerometer. Meaning that if I just stand (without pedaling) on the left crank-arm, it won’t produce a power value, as no angular velocity was occurring. This is expected and logical."
    DCRainmaker

    http://www.dcrainmaker.com/2013/01/s...th-review.html

    http://www.dcrainmaker.com/2013/06/s...ew-update.html

    I live in the UK. Ordering from within the EU is ok but from outside the EU you start getting hit with import duty and fees, especially on high value items.

    The Power2Max power meters built after around September 2012 are all supposed to have temperature correction built in. The older ones can be sent back to Power2Max and upgraded with temperature correction for increased accuracy also.

    http://www.power2max.de/europe/en/pr...ie/service-en/

    On that NZ shopping site they have a picture of the Power2Max triple chainset.



    When compared to a normal Shimano chainset I think I can see what the problem is. Although the Power2Max MTB triple chainset uses standard 104/64 BCD chainrings the mounting holes are rotated, so that the sensor unit can fit in place. The Power2Max MTB double chainset uses 120/80 BCD chainrings but is also rotated in the same way. By rotating the mounting holes it changes the alignment of the chainrings relative to the crankarm and puts one of the chainring bolts directly behind the crankarm. This isn't a big deal with round rings, the shift ramps might not line up as intended and the pin that stops the chain jamming behind the crankarm is removed but that's all.

    Actually changing the chainrings at home still looks possible. It might require removing the Rotor crankarm from the power meter spider to get enough space though.

    If you wanted to use oval chainrings however they can be physically fittted to the chainset but the ovalisation is going to be in the wrong place relative to the crankarm, so that they don't function as intended. That's a tricky one as it probably rules out using Rotor oval Q Rings with the Power2Max.

  8. #8
    mtbr member
    Reputation: sprocketjockey9's Avatar
    Join Date
    Jul 2006
    Posts
    1,215
    DC Rainmaker has since gone against his initial findings on the stages & has recommended it. I've seen the stages lined up agains quarq/srm/power tap. The most inconsistent of them all was the quarq's, due to temp fluctuations & also big/little ring changes. Plus quarqs just always seem to shit the bed

    The stages data I've seen since they have updated for the power spikes & lower cadence has been really great. ProTour guys have been backdooring their sponsors to get hands on them & word on the street is they are gonna go in a big way with a team next year.

    I don't think they are perfect by any means, but for the price & accuracy they are the best choice out there. If you have a significant leg issue, can certainly understand why they wouldn't fit. But for 99% of people...

  9. #9
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I have some mild leg problems. The left leg does a little but I'd estimate it's something like a 95% right leg / 5% left leg power split. It makes finding a suitable power meter harder than it would be normally. The pedalling graph above from DCRainmaker shows what my power output would look like with a Stages power meter. It's a shame as otherwise I probably would get one.

    I had a reply from Power2Max regarding Rotor Q rings and whether my modified left hand crank with a Power2Max power meter would affect the accuracy. It largely confirms what I suspected:

    "thanks for your interest in power2max.

    No, sorry, this is not possible. Currently the MTB version uses the electronics and plastic cover from the road versions. If we rotate the pitch circle, one of the chainrings bolts is covered from the battery compartment. So you cannot mount the chainring. We can´t say at what point it will be possible.

    Regarding your special left crank arm,
    ...
    Regarding the accuracy of the power2max it works perfectly.

    Best regards
    Your power2max Team"
    Power2Max Support

    Another possibility that I've been considering is an SRM power meter. They actually make a Shimano Deore XT SRM now, although they're twice the price of a Power2Max. That has the advantage of working straight away with my current modified Shimano left hand crank. The only issue being that it's a double chainset with 120/ 80 BCD rings so I'd be limited to a 26T inner chainring.

    http://www.srm.de/products/srm-power...himano-xt-mtb/

    .

  10. #10
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I emailed SRM and the Shimano Deore XT SRM chainset is available to buy in the EU. The SRM has a 3 year warranty, compared to 2 years for a Power2Max. According to the product page the SRM looks like it would be around 100g lighter than the Power2Max triple chainset (I don't think the SRM claimed weight includes chainrings so it may not be a full 200g lighter).

    That's great but the Shimano Deore XT SRM only comes in a 120mm/80mm BCD double chainset version. With mountain bike chainrings that means either 38/26T chainrings with an 11-36 10 speed cassette or 39/26T chainrings with an 11-36 10 speed cassette. The 80mm BCD restricts the inner chainring to a minimum of a 26 tooth chainring. Rotor make 38/26T size q rings in 120/80mm BCD so I could run oval chainrings on the SRM.

    My current setup is 44/33/23T triple chainrings with a 10 speed 12-32 cassette. The bottom gear actually works out about the same but I'd lose some top end speed and there are much bigger gaps in the gearing range using a double chainset. On the road I spend most of my time between 15 and 20mph so it's nice to have some options there with relatively close spacing jumps.

    I can't decide if it would work or not. This chart shows the gearing jumps if I switched to a double chainset.



    Extra weight and the hassle of needing to have a new crank made (Power2Max), but with the right gearing, or a lighter option that does everything I want apart from having my preferred gear ratios (SRM) ?

  11. #11
    mtbr member
    Reputation: wetpaint's Avatar
    Join Date
    Sep 2009
    Posts
    313
    IMO, a double looks like it would be fine, you'll lose a couple of mph on the very low end and the top end. I'm really picky about gearing on my road bike, but I don't mind my 11-36 on the MTB for trails.

    For mountain biking on the road or dirt roads, I usually end up in a 38/13 or 38/15 for cruising, it is kind of an annoying jump, but usually the terrain is variable enough that I can make it work.

    I've had great luck with my road SRM, I change out the batteries myself, so it only costs about $20 to change. I had a reed switch go out this summer, the unit is at least 4 years old and they replaced the part under warranty at no charge.

  12. #12
    mtbr member
    Reputation: jcm01's Avatar
    Join Date
    Oct 2011
    Posts
    257
    Quote Originally Posted by sprocketjockey9 View Post
    DC Rainmaker has since gone against his initial findings on the stages & has recommended it. I've seen the stages lined up agains quarq/srm/power tap. The most inconsistent of them all was the quarq's, due to temp fluctuations & also big/little ring changes. Plus quarqs just always seem to shit the bed

    The stages data I've seen since they have updated for the power spikes & lower cadence has been really great. ProTour guys have been backdooring their sponsors to get hands on them & word on the street is they are gonna go in a big way with a team next year.

    I don't think they are perfect by any means, but for the price & accuracy they are the best choice out there..
    ^^This!

  13. #13
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I was thinking a bit more about the gearing on my ride today. I probably could get away with an MTB double chainset at a push.

    The main thing would be losing the 44x12 top gear. I don't really use top gear that much - winding it up down the hills on tarmac occasionally but that's about it, hardly ever offroad. When I do use it it comes in handy though.

    A few weeks ago I was out for a ride and caught somebody on a road bike up a climb. Over the top of the climb the road goes downhill at a gentle slope, too gentle to tuck in and freewheel but downhill enough that pedalling you can easily reach 30mph+. He came back past, dropped me and rode away down this slope, simply because I ran out of gears and couldn't pedal any faster. With a lower top gear this would be an even more frequent occurrence, especially on road club runs where everyone else has higher gearing available and a tendency to wind up the pace before the coffee stop.

    I like the close range on the middle ring too. Being able to upshift one sprocket at a time 15-14-13-12 gives a decent kick when I'm trying to accelerate whilst holding a particular cadence. It also gives a choice of gears for riding tempo on the flat.

    So long as I can keep rebuilding the fitness I'm not too worried about the bottom gear though. With my current setup I have the option of fitting a 36T rear sprocket for a 23x36T bottom gear if needed for major climbing. I use 12-32T sprockets normally for the closer range as I can get up most Cotswold climbs on 23x32T ok. I went up the 10% gradient climb out of town today without too much effort so a 26x36 bottom gear should be fine, although there isn't much of a safety margin if I'm tired or find myself on an unplanned route with monster climbs.

  14. #14
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    There's a bit here about Power2Max zero offset numbers using a Garmin Edge and also the temperature compensation with Power2Max:


    "FROM POWER2MAX:

    Hi Fuji Racer,
    Thanks for your message. The "calibration" function of the Garmin is a bit of a misnomer. It establishes a manual zero by asking the power meter to zero. The result is the same as when you let the power2max do an auto-zero. The calibration of the power meter (also sometimes called the "slope") does not get affected by this.

    There is no harm in doing the Garmin calibration when it starts up, but there is also little benefit, since your power2max rezeros every time you stop pedaling for at least 2 seconds.

    I hope this helps!

    Best
    Nicolas"

    -----------------

    "FROM POWER2MAX:

    Hi,

    The absolute offset value is meaningless. It can vary depending on exactly how strongly you torqued different screws, etc. A 4 point change in the zero offset number would, if you didn't coast and there wasn't any temperature compensation, mean about a 6 watt difference. The 4 points are independent of the starting value, so it doesn't matter if someone has a value of -1000,- 800 or -400 or 0. Please also don't compare them across technologies to SRM or powertap, because each company has a different measurement approach, different units, etc, rendering zero offset comparisons meaningless.

    Our units generally have a very good temperature profile before any temperature compensation. In addition to that we have implemented the temperature compensation mechanism. Your power2max runs through a temperature chamber for several days where we repeatedly cycle it from -20C to +70C. The temperature compensation curve gets recorded like this and programmed into your unit. Each unit gets its own temperature curve. This eliminates the last possibilities of drift.

    It is very dangerous to compare the power2max to other units and take them as given. For example, on my home trainer my power at a given gear and cadence will increase by about 30 watts during a session due to increases in the temperature of the fluid and resulting increases in resistance. If I were to take the home trainer as "constant" I would think my power meter drifted.

    I hope this helps, please don't hesitate to ask any further questions you may have.

    Best
    Nicolas


    https://forums.garmin.com/showthread...e-2-8-Firmware

  15. #15
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I'm still battling with this gearing issue.

    Another option that I'm looking into is having some custom chainrings made for the Power2Max chainset. If I had some custom oval chainrings made, with the same ovalisation as the Rotor rings but rotated to match up with the Power 2Max crank spider, that would give me the gearing I want.

    This company in Australia makes custom chainrings. They look nicely done from the website and include machined shifting ramps too.

    I've sent them an email to see how much it would cost.

    http://www.fetha.com.au/index.html

    .

  16. #16
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I bought a set of donor Rotor 3D cranks with the 24mm axle. The idea being that the left hand crank from it can be modified to go with the Power2Max right hand crank. What I hadn't realised is that the Rotor 3D crank is essentially a low q factor road crank that they've then put a longer axle on.

    In order for the crank to work on a mountain bike they have the longer axle and then the gap is filled with plastic spacers either side.



    My bike uses a PF30 bottom bracket so already has plastic reducers and spacers. With all those existing plastic spacers plus the Rotor plastic spacers the whole bottom bracket is going to be "unapologetically plastic" at this rate.

    There is the Rotor 3D+ 30mm axle version but this has the problem of the axle being integrated into the left hand crank arm (the Rotor 3D 24mm axle version has the axle integrated into the right hand crank arm). It's less hassle if there's just the crank arm and no preload lock ring threads etc to deal with for modifying the left hand crank arm to fit.

    I'm remembering why I went with a Powertap for my power meter previously now. Trying to sort out a suitable chainset with modifications is never straightforward.

  17. #17
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I've made a little progress.

    Fetha have confirmed that they can make the two custom oval chainrings to fit the Power2Max crank spider, allowing me to keep my current triple chainset gearing (44T round ring and then 33 and 23T oval rings) with the powermeter. I've ordered them but due to the Christmas holiday period the rings won't be ready until mid to late January 2014. First impressions from the email correspondence that I've had are good and that the end product will be decent.

    This picture shows a custom CNC Fetha XX1 chainring with narrow wide teeth that they made to use with a 110mm BCD Quarq spider. I think I'm probably going to go for this anodising finish on my chainrings too.

    http://weightweenies.starbike.com/fo...art=45#p999411



    My donor left hand Rotor 3D crank has gone off to be welded and modified into a swing crank also. I can't quite conceptualise how the swing crank is going to work with the correct q factor as yet (due to the narrow width of the Rotor crank compared to the Shimano MTB ones that are easy to modify) but it will hopefully come together sometime before Christmas.

  18. #18
    mtbr member
    Reputation:
    Join Date
    Jan 2008
    Posts
    973
    I'd always read that ovalized chainrings mess with the accuracy of crank spider based powermeters - thinking back to when SRM was really the only game in town. Granted it's not a huge variation (off memory something like 2-3%) but its certainly not helping anything.

    anyhow, has that changed?

  19. #19
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I've read a few things about oval chainrings and crank based power meters. O.symmetric chainrings and SRM power meters were the ones discussed most as Bradley Wiggins was using them. Apparently the more oval the chainring the more of an effect it can have on power readings, causing the crank based power meter to read high:

    Note on non-round chainrings
    ”I’ve had a handful of people ask about how any sort of oval or non-round chainring affects power measurement. Put simply, it does affect crank-based power measurement. The reason has nothing to do with any of these power meters’ quality or design, but rather a simply physical reality: Our power equation that we keep referring to assumes a constant velocity. For a crank-based system, it assumes that your pedals are turning at a perfectly steady speed throughout each complete revolution. For a wheel-based system, it assumes that your wheel is turning at a constant speed. We know that neither of these situations are very likely.

    With oval chainrings, their #1 goal is to mess with this velocity. They cause your crank velocity to change during each pedal stroke, so you spend more or less time in certain parts of that pedal stroke. For example, they may want you to spend more time – slow the crank down – during the main ‘power phase’.

    While we don’t want to dive too deep into this topic, the net effect is that you’ll get slightly inflated power numbers using an oval ring on a crank-based power meter. How much this gets inflated depends on how odd-shaped your ring is (the ‘less-round’ it is, the more your power will read high). How high are we talking? Through the course of my research, I heard anywhere from 0.5% to 4%. I did not have any non-round rings during my testing, so I can’t make a claim based on personal experience.

    Just for fun, let’s say your power meter quotes +/- 1.5% accuracy. At 200 actual watts, that means your displayed power output could be 197 to 203. If your oval chainrings adds another 1.5% on top of that, we have a net of +/- 3%. On the high end, that would tell you that you’re putting out 206 watts, when you’re actually putting out 200. If you haven’t set your zero offset in three weeks, it could drift much farther than that. Did you PR on your Strava segment, or just get bad data?"
    Greg Kopecky - Slowtwitch Power Meter 301 article

    http://www.slowtwitch.com/Tech/Power..._301_3696.html

    Rotor Q rings are a 10% oval so nowhere near as extreme a shape as the O.symmetric rings.

    Power2Max use an accelerometer to measure crank rotation and position, rather than a reed switch and cadence magnet (SRM and Quarq power meters). Power2Max claim that as a result their power meter accuracy is unaffected by using oval chainrings. They also claim that their power meter accuracy is unaffected by uneven chainring bolt torque tightness too, so that you can swap chainrings whenever you like without needing to recalibrate the power meter.

    "Hi,

    Nicolas here from power2max. First of all thanks a lot to Ray for this detailed test. We appreciate very much the time and effort you put into this.

    I would like to offer some information on a few of the key questions asked here, I hope they are helpful:

    Why you can change chain rings without recalibrating: power meters are affected by chain ring changes if what they measure is affected by “where”, i.e. at which chain ring bolt, the force is applied. We call this “rotational variance”. If you manage to eliminate rotational variance then you eliminate the influence of differently flexing chain rings or uneven chain bolt torques. We have managed to eliminate rotational variance in our power meters. How we did it is our secret sauce.

    How often we sample: We use a very high sampling rate of 50Hz, i.e. 50 measurements per second. This gives us very precise measurements and allows you to use oval chain rings without problems".
    Power2Max (Post #33 in comments)

    Post #33 in the comments to this review:
    http://www.dcrainmaker.com/2013/01/p...th-review.html

    I've used Rotor oval Q Rings for several years now. I like them because the pedalling action feels nicer to me when climbing and they appear to give better traction to the rear tyre when pedalling on loose or slippery surfaces (such as loose gravel or mud). I'll often find the rear tyre spinning up trying to ride on the round outer ring through loose gravel for example. At the same speed and conditions on the oval middle ring it's straight through with no drama or wheelspin.

    There's no speed or power improvement with the oval rings that I've experienced however. It's purely because of the feel and traction benefits that I've stuck with them.

    Spinning a big gear on the road I prefer a round ring to an oval, which is why I have a 44T round outer ring. The round outer ring also avoids the front derailleur shifting issues and placement issues that you can run into with oval chainrings.

  20. #20
    mtbr member
    Reputation:
    Join Date
    Jan 2008
    Posts
    973
    Damn. Hopefully you had all those links handy (thanks for making me feel real lazy )!!

    agree why to use the rings, I used them on my cx bikes prior to this year - new drivetrain and they weren't in the budget.

  21. #21
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    Some other links about oval rings and accuracy (see the comments in the first article. This is one of the ones about Bradley Wiggins and O.symmetric rings that I can remember reading: )

    http://cyclingtips.com.au/2012/09/os...ck-or-miracle/

    http://forum.slowtwitch.com/gforum.c...;post=4251821;

    You can't get O.symmetric MTB oval rings, only road versions, but I did see mentioned on Bikeradar today that you can actually get Ogival MTB oval chainrings, including in a narrow wide XX1 single ring version.

    http://www.ogivalring.com/epages/fe4...ateaux_VTT_XX1

    I've no idea what they're like to ride with. That much ovalisation is probably going to feel rather strange and I have visions of the chain coming off if you didn't use a chainguide.

  22. #22
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I've had confirmation that my Power2Max power meter should ship in the week beginning 6 January 2014.

    I bought it direct from Power2Max in Germany in the end, paying by bank transfer. Once you place an online order they send you a confirmation email which contains their bank payment details to send the money to the next day.

    It's actually fairly straightforward to make a direct bank transfer payment overseas via online banking. You enter the euro amount that you want to send and then the online banking displays the current exchange rate and £ GBP amount that will be deducted from your account. My bank charged £4 GBP to make the bank transfer. I copy-pasted the Power2Max bank details from the email into the online payment fields as the IBAN number is quite long. I then spent ages checking it was accurate before pressing submit.

    Here's hoping it was all correct.

  23. #23
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    That's a relief. I just received an email from Power2Max confirming they received the payment.

  24. #24
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    When I ordered the Power2Max power meter on Monday delivery was estimated as the week beginning 6 January 2014.

    I received a courier dispatch email today, with an estimated delivery date for early next week! That's a much faster turn around than I was expecting.

  25. #25
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    The big thread of everything Power2Max on Slowtwitch for reference:

    http://forum.slowtwitch.com/gforum.c...y;so=ASC;mh=25

    My Power2Max powermeter arrived from Germany on Christmas Eve. Based on my one the claimed weights on the website are quite accurate at 918g for my complete Power2Max Rotor 3D triple chainset with 44/32/22 round BOR chainrings. It needs the battery fitting before first use.



    I received in the box - complete assembled Powermeter, manual with the slope printed on the inside cover and the spider removal tool was included. I wasn't sure if the tool would be but it was fortunately.

    What you don't see from the side on pictures is how bulky the powermeter is on the outside of the crank. Compared to a Quarq there's a lot more to it. The coloured ring sticks right out and the battery compartment is chunky too. I think my right foot should still clear it easily though.



    There's no way of removing the outer chainring without removing the crank arm from the spider. The inner rings will come off but the chainring bolt behind the crankarm is too close to remove.



    Because of the chainring orientation there's no chain catcher pin behind the crankarm. If the chain were to come off the outside of the chainring it looks like the chain could potentially jam between the crankarm and spider. I'm probably going to try and do something to prevent that before I ride it. There's only a slim chance of it happening but that's not the same as saying it can't happen.

    I haven't got a modified left hand crank yet so can't use the Powermeter until that's finished sometime in January. The measurements are a lot closer than I'd like so that could still end up as a problem.
    Last edited by WR304; 12-27-2013 at 06:41 AM.

  26. #26
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I've come up with my best crank modification idea yet. I've got a perfectly good modified left hand crank and it will be difficult to make a 13.5mm width swing crank fit properly on a modified Rotor 3D crank arm ( the q factor has to be the same between a modified crank with the added swing crank width included and the original crank to stop my left leg being pushed out too wide). I measured it and there's only 5mm of available width on the Rotor LH crank.

    My thoughts then turned to the right hand crank. The Power2Max powermeter is just the crank spider. This threads onto the right hand crank arm but is only held on by a lock ring. The powermeter spider doesn't require a specific crank arm to function. If the problem is the Rotor crank why not put the powermeter spider onto a different crank arm?

    I have a Shimano Deore XT M770 right hand crank here which is made in two parts (although bonded together by shimano). Looking at it I think that it should be possible to remove the bonded crank spider from the Shimano crank and then add some splines to fit the removable Power2Max spider onto the Shimano crank arm, giving a correct q factor for my leg, triple chainrings and no compatibility issues. The parts of the Shimano crank that would be retained are the right hand crank arm and the axle.

    This video (in German) shows how the Power2max spider is attached to the Rotor crank arm. I have the special tool as it came with the chainset for attaching and removing the crank spider.

    <iframe width="560" height="315" src="//www.youtube.com/embed/HX5pYF0eHXY" frameborder="0" allowfullscreen></iframe>

    Pasculli Power2Max - YouTube






  27. #27
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    My Fetha custom oval chainring arrived from Australia today. What this is is a 33 tooth middle chainring shaped like a Rotor oval chainring, only with the chainring bolt holes rotated so that the oval chainring will have the correct orientation when used on the Power2Max crank spider. The chainring is champagne anodised.



    Getting the actual power meter sorted out has been taking longer than I'd hoped. The problem is that in order to fit the Power2Max crank spider onto a Shimano crank the crank needs some CNC milling doing, in order to create a spline for the crank spider to attach to. My friend's engineering company has been so busy they haven't been able to fit it in yet. There's not much I can do to hurry that along.

  28. #28
    mtbr member
    Reputation:
    Join Date
    Mar 2014
    Posts
    2
    First of all I want to say how much this thread and WR304 has helped me in my search for a Powermeter.
    Kudos and Thanks to you! I value your detailed style of reporting of new information to the Forum.
    Being of similar mindset (detail oriented) I find it refreshing that you leave no variable unexplored and no idea untested. Some of your explorations into the subject of non-standard Powermeter / Crankset applications have significantly shortened my own timeline on becoming an owner.
    I finalized my order with Power2Max today and will post an update once I have the parts in house.
    Thanks for reminding me that I'm not the only one who thinks...
    "Life is too short for off-the-shelf parts!"

  29. #29
    mtbr member
    Reputation:
    Join Date
    Sep 2011
    Posts
    1,795
    I wish PM manufactures would get on the ball with the X11 stuff. The power2max setup looks nice.
    17 Focus o1e
    17 Yeti ASR-cT
    14 Yeti ARC
    16 Bianchi Specialissima
    15 Echo Big Deal

  30. #30
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    Here are a couple of pictures showing how SRM fit their power meter spider onto a Shimano Dura Ace crank. SRM machine a standard Shimano Deore XT crank for their MTB crank so the idea of doing the same with a donor crank in order for it to accept a Power2Max spider looks to be sound. When you remove the spider from a Shimano Deore XT crank there is enough material there to add a spline.

    These pictures are of a Shimano SRM Dura Ace crank with the spider removed so you can see how SRM have machined the Shimano crank:









    This picture shows a SRM power meter fitted to a Rotor 3D crank. Instead of using the Rotor threaded lockring they have chosen to use allen bolts to attach the crank spider onto the crank arm. When making a custom crank this attachment method looks to be the easiest, saving the task of having to create a thread for the lockring



    This picture shows a Power2Max spider (for an FSA crank) which has holes drilled and is designed to be attached via bolts.


  31. #31
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    It's been a long time coming but my Power2Max power meter is finally done!

    It consists of a Shimano Deore XT M770 crank arm that has been modified to fit a triple Power2Max spider. First the steel axle was pressed out, and then the splines from the original Rotor 3D crank were measured using a CMM before being machined into the Shimano crank arm. It was decided that there was enough metal to cut a thread so a threaded lockring was used, rather than my idea of tapping holes. That has the advantage of not voiding the warranty on the Power2Max unit.





    As this was a one off the splines machined into the crank and the splines on the spider match exactly with very tight tolerances, resulting in a closer fit than with the original mass produced parts.



    When assembled this is how the power meter looks side on. The heat marks on the crank arm are from where a blob of weld was added in case there wasn't enough metal to create a spline. This proved to be unnecessary as the entire spline is original crank material.



    This picture shows the chainrings installed and lockring. The outer ring is a BOR 44 tooth round chainring, the middle ring is a Fetha 33 tooth oval ring (with the same ovality as a Rotor Q ring but rotated bolt holes) and the inner ring is a Rotor 23 tooth oval Q ring. This gives me exactly the same gearing as I used before.



    Here's a picture of the crank installed on my bike. Blue decals to match the Garmin Edge 500 head unit. It all seems to be ok. The power meter is detected and sending data to my Garmin Edge 500, the front shifting between chainrings works and the crank feels solid. I'm hopefully going to give it a proper try tomorrow to see what the data looks like.


  32. #32
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    Quote Originally Posted by WR304 View Post
    What you don't see from the side on pictures is how bulky the powermeter is on the outside of the crank. Compared to a Quarq there's a lot more to it. The coloured ring sticks right out and the battery compartment is chunky too. I think my right foot should still clear it easily though.
    ...
    Because of the chainring orientation there's no chain catcher pin behind the crankarm. If the chain were to come off the outside of the chainring it looks like the chain could potentially jam between the crankarm and spider. I'm probably going to try and do something to prevent that before I ride it. There's only a slim chance of it happening but that's not the same as saying it can't happen.
    I got out for the road club ride today and had many chances to find what happens if the chain comes off the outside of the big chainring. My front derailleur was slightly out of adjustment and threw the chain off several times. The missing chain catcher pin on the chainring isn't an issue in use. What happens is that the chain comes off, and then the chain rests on the wide plastic body of the powermeter, instead of jamming. It's a simple task to pedal the chain back on without having to stop. I've sorted it out now by tweaking the front derailleur limit screws but it's useful to know I guess.

    In use the Power2Max power meter was good. Used with a Garmin Edge 500 there were no drop outs or obviously bad data in today's ride file that I could see. The power numbers seemed to be in the same ballpark as what I'd see with my deceased Powertap hub too, although without a side by side comparison using them together on the same ride it's not really possible to say how close the displayed power numbers would actually be between the two power meters.

    It was a nice sunny day and didn't rain so I didn't test the weatherproofing of the power meter.

  33. #33
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    The Power2Max power meter has an estimated left / right leg balance (bottom right figure in the picture of my Garmin below). When riding along without trying hard my balance is around 85% right leg / 15% left leg but at maximum effort, doing 400 watts trying not to get dropped on the club run for example, it evens out for short periods to as much as 65% right leg / 35% left leg. I can't seem to sustain that for long though, only a few seconds.

    The Garmin picture is the summary from today's ride where I was just out by myself, rather than on a group ride. The elapsed time is only more than the ride time because I took the photo before saving the ride file after I got home. There wasn't actually any stopping during the ride itself.

    I averaged 279 watts (4.22w/kg) up the main climb (1.29 miles, 10% gradient, 10 minutes 24 seconds, 7.5mph average speed) and set a personal best time also, 33 seconds better than I managed in 2012 before crashing and having an enforced year off the bike. I was quite pleased with that.



    Here's a more detailed look at the left / right leg balance in rubiTrack for IOS. The top line shows my power output in a short section of today's ride whilst the lower line shows my left / right leg balance as recorded by the Power2Max power meter. As I try harder the balance temporarily becomes more equal. rubiTrack seems to have a bug where left and right are the wrong way round on the graph it displays. I've marked it in text which is which.



    Some Power2Max left- right balance notes:

    "1) Our power meters don't measure left-right balance by using a reed contact to distinguish between 0 to 180 and 180 to 360 degrees, but goes from torque peak to torque peak: it compares the relative power of the left leg power phase with the right leg power phase. So it can be a bit different from Quarq because of the different approach.
    2) The (Garmin head unit) calibration figure has no significance. Any offset changes during the ride (between auto zeros) are compensated by the temperature compensation mechanism.
    ...
    4) No, we have tested oval rings and they don't inflate power - we measure at 50HZ and don't use discrete, event based cadence.

    Best
    Nicolas "
    power2max

    http://forum.slowtwitch.com/cgi-bin/...023818#5023818
    Last edited by WR304; 05-07-2014 at 02:06 PM.

  34. #34
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I've got a few more rides in with the new power meter now. It's all been working ok and it survived its first wet ride today also.

    This is only the second power meter that I've had. The previous one being a Powertap MTB hub. Something that I hadn't realised is that the information displayed by different power meters isn't the same. Due to the way a Powertap hub samples power the number displayed on the Garmin Edge 500 screen using a Powertap hub is very jumpy, making it hard to use for pacing without using a lot of smoothing, as otherwise the display will vary by 100 watts plus every time it updates.

    "Likely the main reason for the variation in power you are seeing is due to the sampling rate (1 or 1.26 Seconds) of the Powertap. The samples are not synchronized to the crank rotation. So although the average power will be correct the individual samples will jump around. This is sometimes referred to as the precession effect. It doesn't affect SRM, Quarq or any other crank based powermeter.

    The simplest solution is to increase the display averaging to 10S. It won't affect the raw data but it will settle down the display."
    gregf83

    http://www.cyclingforums.com/t/48227...-is-this-right

    I thought it was normal and that all power meters would have a display as jumpy as a Powertap. That isn't the case however. The two WKO+ 3.0 graphs below are of the same route on different days, one ride from last year using a Powertap and then one ride from today using a Power2Max crank. What this is trying to illustrate is the difference in stability between what is displayed on screen whilst riding. The Powertap figure jumps around by 100 watts plus whilst the Power2Max is far easier to interpret as the basic information it sends is more consistent, even before it has some smoothing applied.

    In use this is a massive advantage for the Power2Max if you want to use the power numbers for pacing whilst riding. The more stable the power number that you have on screen the easier it is to gauge your effort. I used to have 10 second smoothing on the Garmin display using a Powertap but have been using 3 second smoothing with the Power2Max.

    Powertap hub:


    Power2Max crank:


    One of the concerns I had was that using a triple chainring crank based power meter with a mixture of round and oval chainrings might result in some odd readings. I did a 20 minute FTP test on Monday to try and get a feel for where I am fitness wise. My route starts off on the flat, goes up a hill and then I do a few minutes on the flat after the top to make up the time if necessary. On Monday I reached the top of the hill with two minutes left on the clock and kept the pressure on, shifting straight up to the big ring at the same effort as I had been putting in on the hill.

    The WKO+ 3.0 graph below is an extract showing the final few minutes of the test. I climbed the hill on the 23 tooth Rotor Q ring inner ring at an average power of 279 watts, reached the top of the hill, shifted up and kept going as hard as I could, averaging 279 watts on the flat using the 44 tooth BOR round outer ring also. It's not conclusive but I don't think the mixture of chainrings is going to be an issue.


  35. #35
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    The Power2Max has survived two wet rides now. 8am this morning, pouring with rain up in the hills whilst busting out some intervals. I'd swear I could hear a tiny violin playing.

    If you want to ride in the UK getting rained on is a regular occurrence. It was wet enough that the barometric altimeter on the Garmin Edge 500 stopped and my shoes were full of water by the time I got home so it counts as a proper test. The power data from the Power2Max was fine throughout.

  36. #36
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    One place that I've been seeing some strange behaviour from the Power2Max is after stopping for a bit. This is something I've had happen a few times on rides now. After a fairly long stop, 10 to 15 minutes, when I set off again the power numbers will temporarily be a good 100 watts lower than they should be. It's not every time I stop though, only every now and again.

    This was particularly noticeable today as I was out on the Tuesday club ride. It was dry, fairly warm and sunny. After 15 minutes spent chatting we set off. Immediately after setting off I was on the front of the group, riding along at 18mph and already starting to try a bit. I was probably doing around 200 watts. The power display on the Garmin Edge 500 was saying 100 watts though!

    The problem was that there were riders sitting close behind so I was unable to safely do any extended freewheeling. For the next six minutes the power numbers stayed wrong until on a short downhill section I was able to do two four second freewheels to try and let the power meter sort itself out again. After that the power numbers returned to normal and it was ok for the rest of the ride.



    You can see this clearly in rubiTrack when looking at the ride file. The left - right pedalling balance is normally dynamic and changes all the time. For the first six minutes after setting off the balance doesn't change. After I do some freewheeling the left- right balance starts responding again.


  37. #37
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    What I've been doing if I'm stopped for a long period of time is to spin the cranks backwards a few times before setting off, in an attempt to make sure the power meter wakes up and has a chance to settle down before beginning riding. That seems to be a procedure that works ok as I haven't had any of the odd power readings since then.

    I've been getting out and doing more offroad rides with the Power2Max. If you've read some of DC Rainmakers comments about accelerometers and rough surfaces one of the things that I was wondering was how well the Power2Max accelerometer based cadence would work offroad.

    http://www.dcrainmaker.com/2014/05/g...s-sensors.html

    Riding on the farm tracks and bridleway of the Cotswolds it seems fine, without doing anything notable or out of the ordinary. The graph below is a short extract from today's ride. The first part is on some woodland singletrack. It goes over a series of roots and is then a hardpacked dirt path running around the edge of a field. It's quite bumpy from horses but the bike's suspension deals with it. Part way through I made a mistake, slipping down from the off camber path onto the rough grass, losing some speed. I had to power back up the slope to get back onto the good line again.



    The graph below is another extract from today's ride. This shows a section of farm track which consisted of overgrown dried tractor tracks in ruts. It was very bumpy and you couldn't see what was coming up or avoid the worst of it due to the grass covering the ruts. I had the bike's rear suspension set to full open with no brain platform to try and increase comfort.

    Part way along the track I reached a short but steep slope, rode down it and the bike was bucking so much it was all I could do to hang on. At the bottom there were some deeper muddy ruts before it went uphill. I slowed down, picked my line carefully and then accelerated up the other side of the bank.



    There are a few up and down cadence changes that I'm not completely sure I remember here heading down the bank. I would have spun the cranks whilst downshifting a few gears in preparation for getting through the mud at the bottom though so it's most likely from that. The part where I was definitely freewheeling at the fastest point down the bank has no cadence or power spikes, and that bit was properly rough, so it seems about right.

  38. #38
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    Here are my settings on the Garmin Edge 500. I'm using the 3.30 firmware on my Garmin Edge 500 and have an ANT+ speed sensor:

    System Menu
    Auto Power Down - OFF

    Bike Settings Menu:
    Auto Lap - OFF
    Auto Pause - OFF
    Auto Scroll - OFF
    Start Notice - OFF

    Data Recording
    Cadence - NON-ZERO AVG
    Power - ZERO AVG
    Recording Rate - 1 Second (although it doesn't matter with a Power2Max because it automatically records at 1 second intervals when a power meter is connected)

    Under the Named Bike Option -

    Bike Details
    Wheel Size - CUSTOM and use a manual tyre circumference so that the GPS isn't involved. Whenever you fit different tyres this needs changing. Don't leave it on auto.

    Because an offroad tyre at low pressure compresses so much when you sit on the bike a measured wheel circumference roll out with no weight on the bike is going to be inaccurate (too large a circumference). I typically have a few favourite tyre types that I use most of the time and use a track pump so they always start off at the same pressure for consistency.

    For each tyre at the air pressure that I intend to use I measure the moving wheel circumference whilst actually riding by putting a small blob of white grease on the centre of the tyre tread (something that is easy to identify, will leave a mark and show up on the ground) and then ride along on the bike for a few metres sitting in the saddle as I would normally. The front and rear tyres compress different amounts so you need to measure the one that your wheel magnet and sensor will be attached to.

    Using a tape measure you then go back and measure the distance between two of the white blobs left on the ground as the wheel rotated. That distance is your actual moving wheel circumference to enter into the computer settings for that particular tyre. That ought to give you accurate distance measurements.

    ANT+ Spd/Cad - YES (individual Spd Sensor)

    ANT+ Power - YES

    Sensors
    For speed I have a VDO Z1 ANT+ speed sensor, although any ANT+ speed sensor should work. Bontrager sensors have worked well for me also.

    http://www.vdo-series-z.com/downloads/zubehoer_en.pdf

    Bontrager: node



    Here's an example of why I have a speed sensor instead of relying on GPS speed from the Garmin Edge 500. This graph shows the GPS speed trace on a wooded climb under tree cover, where I was travelling at low speed with obscured GPS reception, overlaid with the speed trace from my old Powertap hub. The speed readings from the Garmin are way out and very inaccurate making it useless for any type of analysis.



    Screen Display
    When riding I like to have quite a basic display as my main screen, something that's easy to glance at and take in offroad. If you have lots of different items displayed it makes it harder to identify what you're after so you spend more time staring at your stem instead of the trail ahead. As you add more items each one becomes smaller also. With the Power2Max I have "Power 3s Avg" as the top line of the display. This makes it largest and most obvious.

    Below that I have "Speed" and below that I have "Time". I like to have speed displayed to have an idea of when to change gear. I use time as a guide for making sure I remember to eat and drink regularly.



    I then have a secondary summary screen, as shown in Post #33 . This is for looking at the ride summary when I get home before saving the ride as the History screen on the Garmin Edge 500 doesn't have much detail.

  39. #39
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    Quote Originally Posted by WR304 View Post
    The more stable the power number that you have on screen the easier it is to gauge your effort. I used to have 10 second smoothing on the Garmin display using a Powertap but have been using 3 second smoothing with the Power2Max.
    The weather was quite bad this morning so I only did a short road ride in the rain.

    I decided to do the ride trying to stay at 200 watts throughout, using the Power2Max power display to pace myself. This graph shows the entire ride with 1 minute smoothing applied. By adding more smoothing to the graph it makes the overall trends more obvious. The yellow dotted line shows the 200 watts that I was targeting.



    Although the blue speed trace varies the power output is mostly in the right area. I brought the pace up a little for the final 20 minutes. There were a few junctions, traffic lights and two u- turns (trying to find a gap in the rain) so it's not exact. On a turbo trainer you'd expect a perfect match but that's not really possible outdoors.



    This shows the detail summary for the ride. If you look at the average power and normalized power figures they're quite close, 201 watts average power and 208 watts normalized power, showing that the ride was at a fairly constant pace. The more variable the ride (hills, descents, lots of sprinting etc) the bigger the difference between average and normalized power is likely to be.

    The other thing to look at here is the power bests for each duration. Because I was aiming for a steady pace for just over an hour of riding the short duration power bests are close to the best one hour power. Any time the power and effort started going too high I would back it down. At the same time I'd try and keep the pace at the target on the downhills also, which means going straight up through the gears to maintain the wattage.



    This shows the power distribution for the ride. I spent most of my time close to my target of 200 watts. I was quite pleased with the 0-20 watt figure too. 3 minutes 8 seconds, 4.3% of a 1 hour 13 minute ride spent freewheeling isn't too bad. That was mostly down to junctions too, rather than freewheeling for a rest.

  40. #40
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    One of the things that I find a power meter useful for is stopping myself getting too carried away and overdoing it. I frequently have a habit of digging a deep hole with lots of riding but then not having enough rest to actually bank the fitness improvements:



    In WKO+ 3.0 you have the PMC (Performance Management Chart). This attempts to give you an overview of your riding, including how well recovered you are.

    http://help.trainingpeaks.com/entrie...nagement-Chart

    Here's my PMC for May 2014 and the start of June 2014. May was a fairly solid month with 74 hours riding. The blue bars show the TSS for each ride.



    If you look at the yellow line in this chart this is the TSB (Training Stress Balance). A TSB score of 0 or higher is supposed to show that you're well recovered. The lower the negative TSB score the more fatigue you have building up. I managed a negative TSB score of -94 somehow.

    After a few weeks of this I decided it was time for an enforced rest. The green highlighted area shows where I took a rest week.

    Here are a few extracts from my notes:

    02 June 2014 - no riding
    03 June 2014 - no riding
    04 June 2014 - no riding

    05 June 2014 - 2 hours 14 minutes riding, 120 watts average power
    "gentle recovery ride, legs very sore, took it easy throughout, nice day, quite warm and sunny."

    06 June 2014 - 2 hours 12 minutes riding, 116 watts average power
    "gentle recovery ride, felt better than yesterday, legs weren't sore whilst riding but still a bit sore afterwards, put in a few efforts during last five minutes or so and they were ok, nice day, quite warm."

    07 June 2014 - no riding

    08 June 2014 - 2 hours 25 minutes riding, 108 watts average power
    "gentle recovery ride, felt ok, having to try to concentrate on keeping pace down, legs were ok no soreness."

    It's surprisingly hard to keep the intensity right down. You have to really pay attention to what you're doing as otherwise the power output starts creeping upwards. This graph shows part of Sunday's ride where I was trying to keep the pace down. It meant going as slowly as 5.3mph in bottom gear up this rise.

    Last edited by WR304; 06-10-2014 at 11:56 AM.

  41. #41
    It's the axle
    Reputation: Gregg K's Avatar
    Join Date
    Jan 2004
    Posts
    1,655
    This is an amazing thread. I haven't even read all of it,, but I can see tons of interesting information in it. That crank modification is a thread all on it's own. I know what's involved, and I don't even know how they held the part. Great stuff!
    Note to self: 85% of FTP for 20 min.

  42. #42
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    My Power2Max power meter has been working well so far. It's done 225 hours riding, including plenty of wet rides in heavy rain, and I really don't have anything bad to say about it.

    I did have an interesting occurrence in today's ride though, a power spike. I was freewheeling, hit a rough patch at speed, with the bike slightly unweighted, and the power meter reported a 878 watt power reading in error.



    That's notable in that it's the first time I've had it do that. I haven't seen that happen before which is why I'm mentioning it. The rest of the ride file looks fine with nothing else odd or out of the ordinary.

    The power meter battery is supposed to last 400 hours before needing replacing. Apparently you get a low battery warning appear on the Garmin Edge 500 screen also with a Power2Max. I've bought a few replacement Renata CR2450N batteries off Amazon to be on the safe side.

  43. #43
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I was so disappointed by getting dropped on the club ride on Tuesday that I did the last part of the route again the day after by myself. The club ride was in a group of four riders (including me). They were having a steady ride whilst I was trying fairly hard to keep up. On the flat main road section, despite sitting in at what should have been a do-able power output, I blew up completely. I wasn't happy with that and decided a second try was needed.

    The two graphs of the same route viewed together give quite a nice summary of what power output on a group ride looks like compared to a solo ride. You can see how on the group ride my power output goes up and down repeatedly with frequent spikes well above 235 watts, and also frequent drops below 235 watts. I didn't spend much time on the front, the speed was dictated by the other riders.

    On the solo ride riding at my own pace I was aiming for around 235 watts and riding as fast as I could. If you look at the two graphs alongside one another the main thing to note is that there are fewer high power spikes on the solo ride graph. Even though I was trying hard that meant maintaining a constant tempo. If you put in a short hard burst it takes time to recover from that. At the same time there are fewer low power sections as I was trying to keep the pace high on the flat and downhill sections.








    On the first climb I was 13 seconds slower by myself, due to spinning a lower gear on the steepest section to not go too far into the red. With the club I'd put in a big effort near the top of the climb to keep up. I then pushed hard on the rolling roads over the top, 20 seconds faster than the club ride. From the top of the hill down to the main road I pulled out another 22 seconds, so that by the time I reached the main road I was 31 seconds ahead of the club ride.

    That still left the 9.55 miles of the main road to go though! With a strong rider riding tempo on the front the average speed along the main road to where I was dropped had been 7 miles in 18 minutes 53 seconds at an average power of 205 watts and an average speed of 22.2mph. On the club ride I'd been sitting in drafting and that pace would be hard to match by myself.

    Going as hard as I could by myself along the main road to the point where I was dropped I managed 7 miles in 19 minutes 59 seconds at an average power of 229 watts and an average speed of 21mph. 66 seconds slower than with the club.

    On Tuesday's club ride I then blew up spectacularly. The remaining 2.55 miles to the junction took me 10 minutes 2 seconds at an average power of 140 watts and an average speed of 15.6mph.

    Wednesday I was ok and kept the hammer down all the way. 7 minutes 40 seconds at an average power of 238 watts and an average 20 mph. It shows how much of a difference an extra 100 watts makes as I made up 142 seconds in just 2.55 miles.

    Overall I was 105 seconds quicker solo compared to the steady club ride but that was a big effort. I then gently rolled home, getting caught in the rain and soaked again...

  44. #44
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    Doing a fair comparison for accuracy between different models of power meter is notoriously difficult. See the first section of this dcrainmaker review where he discusses the issues:

    http://www.dcrainmaker.com/2013/06/s...ew-update.html

    Something I've been meaning to post for a while now is my Mean Maximal Power Chart for 2012 and 2014. As my PowerTap hub broke I didn't have a chance to ride with both the PowerTap and Power2Max recording at the same time to see if there were differences between them. Whether the same effort I was putting in would appear as the same power output on both power meters.

    I've done around 250 hours riding with the Power2Max power meter with plenty of hard rides and interval sessions now. The Mean Maximal Power Chart is a logarithmic chart that shows your best power outputs. In WKO+ 3.0 you can overlay this with best power outputs for different dates. In 2012 I only used a PowerTap hub whilst in 2014 I've only used the Power2Max crank based power meter.





    What's immediately obvious is that there's a big difference between 2012 and 2014 at short durations whilst sprinting, up to around 30 seconds. The PowerTap reading much higher than the Power2Max. This may be because I'm not putting out as much peak power (due to having damaged my left leg even more in 2012 and having to go to an even shorter left hand crank) but it is quite striking. My suspicion is that this might be a difference between the power meters as I feel that I'm sprinting close to how I was in 2012.

    At longer durations the two years are closer, the PowerTap consistently reading higher but not by a massive amount.

    In terms of speed I've been setting climbing personal bests and quicker times by several minutes over longer routes than in 2012 (on the same Specialized Epic and Ground Control tyres).

  45. #45
    mtbr member
    Reputation: wetpaint's Avatar
    Join Date
    Sep 2009
    Posts
    313
    Regarding the peak power, I think you're correct about the difference between powermeters. I have a Powertap on my moutain bike and SRM and Quarq on my road bikes. I've always been able to make about 50w more for peak power on my mountain bike than my road bikes. I'm pretty sure it's just the Powertap reading higher than crank based, as my two road powermeters are always pretty much dead on (5-10w) for peak power.

  46. #46
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    That is one disadvantage of having multiple bikes and several power meters, knowing whether the data that you record from each one is comparable or not.

    Ideally they'd all read exactly the same but in practice there always seems to be some variation between units. It's not a huge deal for me fortunately because I use the one bike for everything. Whether I'm out getting dropped on the road club rides or dodging cattle offroad on a muddy bridleway up in the hills it's the same power meter. So far it seems consistent with itself anyway.

  47. #47
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    Power2Max have announced their newer Type S power meter for mountain bike cranks now. The Type S has been around for a while on road cranks since the start of this year so it was about time. The main differences are that the Type S power meter is less bulky and should be around 100g lighter than the Classic Power2Max power meter that I have.

    It's available as a 1x crank also and is supposed to be available in October:

    http://www.dcrainmaker.com/2014/08/p...dditional.html


  48. #48
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    When the Power2Max battery begins to get low you get a "Power Meter Battery Low" message appear on the screen of the Garmin Edge 500. I had it appear around 2 hours into today's ride. There must be a safety margin built in as the power meter kept working. The battery lasted around 315 hours, less than the claimed 400 hours.

    Unfortunately at the 3 hour point of the same ride my right hand crank snapped. I'd just gone off a speed hump in the high street and was overtaking a car when my right pedal started feeling very odd, as though the pedal axle was bent or my cleat had come out of the shoe. I stopped and realised the crank had failed.

    From the beginning of May 2014 to 22 September 2014 that crank had done 315 hours riding / 4681 miles. Not a huge amount of miles but I do put full power through the right crank. When it broke it didn't come apart completely fortunately so I was able to stop safely and ring for a lift home, my second mechanical failure needing a lift home in two weeks. Ironically, it was only half a mile or so from the roundabout where I crashed and broke my leg in 2012.

    The Shimano crank was modified with material machined from it and some welding done (which would soften the aluminium also) to get the Power2Max spider on originally. It failed as a result of the modification. Where it's snapped the metal looks very thin. I'm going to take it over tomorrow to take it apart and have a think about how the next version can be improved.






  49. #49
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    I took the broken Shimano Deore XT crank over to my friend's factory today to look at. He cut it open to examine the cross section of the crank where it had failed.

    In the picture below you can see how the original crank casting was uneven in thickness, before it was modified, with one half of the crank being thicker than the other half of the crank. In normal use this would probably have been fine but during the process of fitting the custom spider material was machined off the flat on the inside of the crank. This left the inside of the crank very thin, less than 1mm thick at the narrowest point.

    It's at this narrowest point that the crank eventually failed yesterday.

    The plan for version 2 is to use a Shimano Deore M615 chainset instead of a Shimano Deore XT chainset. The cheaper Deore M615 chainset uses solid crank arms, rather than the hollow crankarms of the Deore XT chainset. This should avoid the problem of it breaking in the same place again as there will be more metal there.

    The machined spline and threads on the crank looked great with no signs of any problems in those areas.

    Last edited by WR304; 09-26-2014 at 12:20 PM.

  50. #50
    It's the axle
    Reputation: Gregg K's Avatar
    Join Date
    Jan 2004
    Posts
    1,655
    Between the torque due to the pedal about the crank arm, and the crank about the axle, it looks like the shear forces were highest at the thinnest part of the wall. It's an odd fracture, that I can only explain due to shear forces. But then you knew you were working with a hollow structure. I'd have been nervous riding that. I actually thought it was a solid crank until seeing this photo. Another additional contribution to failure could have been stresses due to notches from machining.

    It's often interesting to modify things.

    I was just looking at plans for a house that is going to be cantilevered out over an 80 foot high bluff over the ocean. The whole house sits on one 3 foot diameter column. It's really cool. We were mulling over the way it might behave in various seismic modes. I wouldn't want to be the engineer responsible for that thing.
    Note to self: 85% of FTP for 20 min.

  51. #51
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    My thinking behind the original Shimano Deore XT M770 crank was that as SRM sell a modified version (see the SRM modified Dura Ace crank arm pictures in post #30) it would be ok to modify it for this also. The wall thicknesses vary across a Shimano crank. I'd seen the top cross section of an XT crank previously but hadn't seen a lower cut cross section.

    This picture shows the upper section of a Shimano Deore XT M770 crank arm. It's much thicker at this point.



    I didn't crash so it's a case of moving on and learning to avoid repeating the same mistakes again.

    My Shimano Deore M615 crank turned up today. Here are some pictures showing the rear of the solid crankarm. If you look at the shape of the crank arm this is a solid crank, rather than the hollow crank arms on the higher end models. It still has the two piece spider and crank arm so will come apart for modification.



    One slight concern is that the Deore M615 crank is shaped and has quite a deep cutout underneath the spider behind the crank arm. That might possibly interfere with machining a spline into the crank if there isn't enough metal there.



    It's going to be a case of having to wait for at least a few weeks before my friend can fit the work in at his factory so I've been using my old crank and riding on feel (who needs a power meter anyway? )

    One thing I find interesting is how riding with and without a power meter affects me psychologically. With a power meter I tend to gauge my effort and pace to it. That works well over longer rides in particular. At the same time it also acts as a "rev limiter" sometimes where I could go harder and it's a distraction.

    Without a power meter on the stem I tend to just blast up everything as fast as possible if I'm feeling ok. That works well up to around the three hour mark.

  52. #52
    It's the axle
    Reputation: Gregg K's Avatar
    Join Date
    Jan 2004
    Posts
    1,655
    That's the same reason I'm looking forward to a power meter. I tend to ride race pace everywhere.

    This project reminds me of when I was fitting a Datsun alternator onto a Norton Commando. I remember searching motorcycle junkyards for the right alternator. Before that, I was taking alternators apart, and machining special fittings to get cases and cranks and rotors all lined up. I had all but forgotten about that until now. But I think what you're doing has way more merit. I graduated from motorcycles to mountain bikes a long time ago.
    Note to self: 85% of FTP for 20 min.

  53. #53
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I picked up my new version of the crank today. It's had the same machining done as on the previous crank. This one uses a solid Shimano Deore crank arm with no welding involved however, which should avoid the problem that I had with the hollow crank arm breaking.

    I haven't tried it yet but it looks to be solid and should hopefully hold up better.


  54. #54
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    I did a few hours riding with the new crank today and it was great. No strange noises or play from the modified crank, it all felt aligned whilst pedalling and the front shifting was better than with version 1. Version 1 (using the Shimano Deore XT crank) didn't have quite the right chainline (the rings had to be moved further inboard relative to the crank arm) but on this crank the chainline is very close to ideal.

    I'm not a huge fan of BOR chainrings though. My outer BOR 44T chainring seems to be made of cheese. I think BOR have made the ring too flimsy as it's prone to bending out of shape. I trued it up with a spanner which seems to have helped.

    I'd fitted a new Renata CR2450N battery in the power meter also. When doing this on the classic Power2Max the three screws for the battery compartment are small. I'd recommend considering taking the crank off the bike and doing it on a table to make certain you don't lose them. When you've changed the battery there is a small LED inside the battery compartment which will flash green when you move the crank to show it's functional.

    The power readings seemed to be the same as normal today. I did have one strange occurrence. A 1000 watt power spike whilst freewheeling 1 hour 50 minutes into the ride. Possibly it was like the other spikes I've seen in the past where I was changing gear, turning the cranks round but with no pressure on the pedals. It was only once in a 3 hour 11 minute ride though.


  55. #55
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I did three hours on the bike today and there were no power spikes. It seems to be a rare occurrence if you manage a particular action. I think it's something like freewheeling, starting pedalling and stopping pedalling again, or a fast downwards movement of the crank with very little load on possibly.

    I have a Chris King PF30 ceramic bottom bracket fitted but because I'm using a Shimano Hollowtech II crank with a 24mm diameter spindle (instead of a PF30 crank with 30mm diameter spindle) I have to have the 24mm plastic reducers installed. The Shimano crank uses a plastic preload bolt which I didn't feel was up to the job of holding the adjustment. The plastic bottom bracket reducers would keep developing free play that you could feel as the crank slopping around. I'd have to repeatedly adjust it every few weeks which was really annoying.

    At the same time as the new crank my friend had a new preload bolt made. Instead of being plastic this one is made from aluminium and uses a 10mm allen key to adjust the preload. This is similar to the metal preload bolts that you get with other manufacturers cranks (Rotor, SRAM etc) and should be up to keeping the bottom bracket in adjustment.



    It's not power meter related but I've got a new SRAM X0 Type 2 rear derailleur on now as well. The drivetrain is so much quieter over the bumps with a clutched rear derailleur.

  56. #56
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    The aluminium preload bolt worked better than the original plastic one but I was still unhappy with the bottom bracket reducers in the Chris King PF30 bottom bracket. It was staying in adjustment but water getting in the gap between the plastic reducer and steel bottom bracket axle was causing the axle to rust badly.

    As part of the refresh to fix the most pressing issues with my bike (new suspension pivot bearings, fork and brain rear shock service, new headset) I replaced the Chris King bottom bracket with a Praxis conversion bottom bracket. This eliminates the need for plastic reducers when using a 24mm diameter Shimano crank in a PF30 frame.

    https://praxiscycles.com/conversion-bb/



    My bike with the Power2Max custom crank mark two fitted. My winter shoes have been rubbing on the crank, taking some off the black paint off the crank arm.



    Riding today the new Praxis bottom bracket seemed ok. The real test is seeing how well it lasts over the winter. My previous Chris King PF30 bottom bracket did 883 hours/ 12,851 miles and the bearings in that were still just about acceptable.

  57. #57
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I didn't have the Power2Max power meter last winter so it's only really now that I've been doing any riding in the cold with it.

    One of its main features is temperature compensation. Whenever you stop pedalling and freewheel the power meter automatically re-calibrates itself to take account of changes in temperature, so that in theory the power readings will stay consistent throughout a ride, even when there are large swings in temperature.

    I've been reading this thread on the subject with interest:

    BikeRadar.com ? View topic - Power Meter Temperature Drift, Or Sharp Decline In Fitness?

    I got home early enough to fit in a quick ride this afternoon before it got dark. As it was a Friday I didn't feel like navigating the town traffic so went straight up a climb into the hills. Because I was in a hurry the bike went immediately from being indoors (around 14c/ 58f room temperature) to out and riding. In the valley it was around 9c/48f but it was much colder on top of the hills (around 5c/41f).

    As I was riding uphill I rode for around 12 minutes with no freewheeling whilst the temperature dropped significantly at the same time.



    When I got to the top of the hill there is a false flat. I was still trying but the power meter was saying that I was only doing 136 watts! That was clearly wrong as I wasn't going that gently. When the display stayed at that level I decided it was time to try freewheeling. I then freewheeled for a few seconds to try and re-calibrate the power meter (long enough to let the head unit power display go to zero) and sure enough when I started pedalling again the power meter was showing 159 watts, rather than 136 watts, for the same perceived effort. That's quite a big difference.

    Here's a zoomed section of the graph showing my power output at the top of the hill after 12 minutes of pedalling, freewheeling to re-calibrate, and then the higher power output afterwards:



    The main thing to remember I think is that the Power2Max needs you to deliberately freewheel from time to time, especially near the start of a winter ride, otherwise the automatic temperature calibration won't happen and your power numbers will start drifting significantly as a result.

  58. #58
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929

    Power2Max MTB Power Meter

    I had a clear strategy for today's ride. This time I would try and freewheel every 5 minutes or so at the beginning of the ride, in order to allow the Power2Max to re-calibrate and adjust to the changes in temperature. It was a different route, with some flat before the first climb of the day, so do-able.

    I waited until 11.45am to find the warmest part of the day when the roads would hopefully be a bit less icy (it was 50/50 whether to just do some turbo training and not risk it). First thing it had been a hard white frost and frozen but it was beginning to thaw and up to 4c /39f by the time I set off. Even so, as I turned out of the drive onto the main A road, which was in the shade, headed towards the traffic lights and then started braking lightly the back wheel locked up immediately. Point taken. It was slippery as anything so I stuck to the main roads.

    This graph shows the first 30 minutes of the ride. The drops to 0 watts of the yellow power trace show where I was freewheeling, for several seconds each time to allow the Power2Max to re-calibrate. Around every 5 minutes seemed about right. On the 9 minute climb I freewheeled at the bottom but then rode up it without any freewheeling, the longest period of pedalling. The power looks ok to begin with but the final few minutes of the climb (after 9 minutes of pedalling continuously) are maybe lower than I would expect. Apart from that one section I was freewheeling roughly every five minutes and there was nothing obviously wrong with the power readings that I was seeing in between.



    Some temperature notes: I leave my Garmin Edge 500 head unit stood outside for 20 minutes or so before setting off. This allows the temperature, barometer and satellite lock to sort itself out fully before I begin riding. This is why the temperature begins at 4c (rather than the much higher room temperature).

    I keep the bike inside before setting off however. Leaving the bike outside would be better for the Power2Max calibration (as it would begin at outdoor temperature and not have to adjust itself so much) but I feel it's a little nicer on cold days to have the bike contact points (saddle and grips) start off warmer, rather than freezing cold.

  59. #59
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    I had a 2900 watt power spike today. I'd been riding along the canal towpath and stopped to open a five bar gate. The bike was leaned up and pushed around for close to two minutes as it was a stiff latch. When I set off the very first pedal stroke registered as a big power spike before it re-calibrated as I freewheeled.

    All I can think of is that moving the bike around or leaning it up whilst doing the gate might have affected the calibration somehow. It was the only spike in the 3 hour 49 minute hour ride, no other anomalies in the file before or after.



    These occurrences are very rare which is why when they do happen I've been posting them here. The rest of the time the power meter has been trouble free, impressively surviving being used throughout the UK winter with no drama.

  60. #60
    mtbr member
    Reputation:
    Join Date
    Jul 2012
    Posts
    541
    After some trouble with my credit card that ended up with Chase having to send me a new one, I finally placed my order last night. Thanks again for your advice WR304. P2M wasn't even really on my radar, but it suits my needs perfectly at barely half the price of an SRM.

  61. #61
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    Quote Originally Posted by bloodninja View Post
    After some trouble with my credit card that ended up with Chase having to send me a new one, I finally placed my order last night. Thanks again for your advice WR304. P2M wasn't even really on my radar, but it suits my needs perfectly at barely half the price of an SRM.
    Which chainrings are you going with?

    My Power2Max is the older classic version. The newer Power2Max Type S power meter has a 110/60mm BCD spider for the double chainring version and a 104mm BCD spider for the single chainring version. There are lots of 104mm BCD narrow - wide rings available but the 110/60mm BCD of the Power2Max Type S double chainring spider is intended for Rotor chainrings, either the no-q round rings or oval q-rings.

    110/60mm BCD chainring sizes currently available in the Rotor rings that will fit the Power2Max Type S double crank spider:

    No-Q Rings (Standard Round Chainrings)
    Outer Ring 42T, 40T, 39T, 38T, 36T
    Inner Ring 26T, 24T, 22T

    http://www.velotechservices.co.uk/sh...od4.asp?cat=31

    Q-Rings (Oval Chainrings)
    Outer ring 40T, 38T, 36T
    Inner Ring 27T, 26T, 25T, 22T

    http://www.velotechservices.co.uk/sh...od4.asp?cat=67

    For making sense of offroad power data I feel it's worth having a seperate speed sensor on the bike. This gives you a more reliable speed trace than relying on GPS, so that if you wish to you can zoom right in and look at your power on a particular section in detail, using the speed trace as an anchor to identify exactly where you were on technical stop start sections and obstacles (accelerating out of a switchback, riding over roots etc). Without a decent speed trace this is far harder to do.

    There was an interesting picture of Alban Lakata's bike from the 2015 Cape Epic. He has an SRM power meter and in the background of the shot you can see his ANT+ speed sensor mounted on the rear wheel also:



    http://www.bikeradar.com/mtb/gear/ar...-lux-cf-43865/

  62. #62
    mtbr member
    Reputation:
    Join Date
    Dec 2013
    Posts
    5
    Man WR304 I have nothing to add to this discussion but I just wanna say thank you, you post are always so detailed and well though that are a pleasure to read. You have contributed so much to this forums that they should give you a trophy.

    I don't write here much but I always visit the forums and try to read your post, I've gained so much insight from your post in my short career MTBing that I really feel in debt to people like you.

    Again thanks a lot.

  63. #63
    mtbr member
    Reputation:
    Join Date
    Jul 2012
    Posts
    541
    I went with Rotor round chainrings, in 38/24. It's a little annoying to get locked into Rotor chainrings due to the unusual BCD, since they're about 50% more expensive than comparable SRAM/Shimano stuff. I guess it's a drop in the bucket though relative to the cost of the whole setup .

    I agree with you completely on not relying on GPS for speed/distance data. I run a Garmin magnetless speed sensor.

  64. #64
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    Power2Max do seem to like non standard chainring bolt layouts for their MTB spiders. I had to order a custom middle chainring from Fetha in Australia to fit on my Power2Max Classic due to its rotated layout. That chainring is still going strong and working well. The teeth are getting hooked but should last a few months yet.

    I got a low battery warning for the power meter whilst riding today. The battery warning appears as an alert filling the Garmin Edge 500 head unit screen and you have to press the Enter button to cancel it so it's hard to miss. Since last replacing the Renata CR2450N battery in late October 2014 I'd done 294 hours riding, a little less than with the first battery. Riding in the cold reduces battery life so it was probably to be expected.

    I took the crank off the bike and replaced the battery seated at a table so that there was no danger of losing the three small screws for the battery compartment (last time I dropped one of the screws and it took lots of searching on the floor to find it again! ). It all looked very clean and dry inside and went back together with no drama.

  65. #65
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    I realised that I haven't actually posted much offroad power data recorded with my Power2Max in this thread.

    Here are a few extracts from today's ride. The full ride was 37 miles with around 24 miles of that being offroad on a mixture of surfaces and terrain, some open grassland, some rutted tracks used by motocross bikes, some farm tracks and some byway (dirt road). I'd made a few changes to the bike's suspension settings and had my act together for once. I rode everything cleanly apart from about 10 metres of muddy ruts.

    Common - Grass Surface



    This graph shows a section of the ride where I was riding over the common. This is open grass land interspersed with a few humps, natural worn paths and small dropoffs to ride off for fun.

    The main thing that the power meter shows here is that riding on grass is hard work. The increased rolling resistance meant that as soon as I turned off from the tarmac road my speed dropped and I was having to put out 200 watts just to ride at a steady 10mph on the flat. Where there was a small rise to get up onto a rocky path you can see how I put in a short burst at 300 watts, lasting just a few seconds. As soon as I was on the path, which has lower rolling resistance than the grass that I had been riding on, my power drops but my speed increases straight away. What you can use this type of information for is to decide your lines. If you have a choice between riding on grass or a firmer surface (hardpacked dirt, gravel etc) trying to stay off the grass is likely to see you travelling faster for the same or less effort.

    Short Steep Hill - Deep Gravel



    This graph shows a section of the ride where I was riding up a short steep rise, the steepest part being 20% gradient. This took me 47 seconds at an average power of 290 watts.

    Along with being steep I was climbing on a deep loose gravel surface so traction was a real concern. For this climb I was seated right on the nose of the saddle in bottom gear. On the steepest 20% gradient section I was doing 394 watts at an average speed of 5.4mph. If you look at the blue speed trace you can see how on this steep section my speed was dropping. If this had been much longer I would have been in trouble!

    Fortunately the gradient eased so I got a quick rest, my power dropping to 225 watts, before the final push to the gate at the top. Although this final part was only 12% gradient it also had the loosest deepest gravel so I was back up to 302 watts.

    On this graph I have the green cadence trace displayed. The cadence gives an insight into my technique when trying to get up this steep hill whilst also maintaining traction on a loose surface. To avoid breaking the wheel free with big torque spikes (from too much downstroke pressure by my stronger right leg) in the gravel I was revving at a high cadence, over 100rpm on the steep sections. I'd guess that if you could see my pedal force through the entire stroke that would see a smoother application of torque than if I was pedalling at a lower cadence.

    Byway (Dirt Road)



    This graph shows me riding along a 10 minute section of byway (dirt road). This road surface consists of hard packed gravel / mud. If you compare my power output to riding on grass there's a big difference. Here on hard pack I'm averaging 13.6mph at just 137 watts average power. On the grass in the same ride it took a much higher power output of 200 watts to average just 10 mph.

    You'll often see generalised comments about how riding offroad power output is always very bursty with big swings in power output and cadence. This really depends on terrain however. Where you live and the trails you ride makes a big difference to what your power files will look like.

    If you're riding here in the Cotswolds a lot of the offroad riding is on farm tracks and bridleway. It can be muddy, bumpy and rutted but in terms of the effort and power output required this type of terrain is mostly about constant efforts. The bike's full suspension may be getting a hammering but when you see the power output on a graph it's steady. Decent fitness is a big factor.

    In the graph above you can see how I'm pedalling along this byway at a 92rpm cadence. I freewheel a few times and have to brake for a lunatic pheasant. Apart from that it's a steady pace. There isn't a great deal going on, and that's the whole point of this graph. On longer duration mountain bike rides in particular don't automatically expect every part of the ride offroad to be a mass of power spikes. It isn't always like that, especially if you're doing fire road and dirt road sections. Smooth singletrack can often be similar in terms of power output too. This sounds incredibly obvious but is an important thing to remember at the same time.

  66. #66
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    Dcrainmaker has posted a review of the Power2Max Type S road power meter.

    http://www.dcrainmaker.com/2015/03/t...th-review.html

    Scroll down to the section on power balance and his 84% / 16% left - right balance whilst pedalling with just one leg picture. Those balance percentages seem strangely familiar to me. All he needed to do was unclip his left foot and pedal with the right leg instead and it would look just like one of my rides.



    In the comments section there are some posts about battery life and also power readings. When I've had a Power2Max power meter low battery warning appear on my Garmin Edge 500 I've replaced the battery at the end of the ride before riding again. I wasn't sure how much life was left after the warning. Battery warnings are sometimes conservative so I thought there might have been quite a bit. Reading the comments someone says that they had a low battery warning, and then the power meter shut down an hour later. It's probably best to be safe than sorry and assume that if there's a low battery warning it needs a new battery.

    The comments posts about having power readings slightly lower on the Power2Max (2 to 7% lower compared to other brands) were interesting. There are several posts about this, including one that mentions not just lower steady state readings but also substantially lower peak power values from a Power2Max than a Powertap hub. That matches up with my peak power curve and the lower power values in Post #44 of this thread too.

    Quoted from comments section of dcrainmaker Power2Max Type S review:

    ----------------------------

    "Have you experienced the Power2Max reading a slight bit lower than other power meters (i.e. Quarq or Computrainer)? Both myself and a friend moved to Power2Max Type S units from Quarq. Subjectively I felt like the Power2Max read about 5% lower than the Quarq. My friend felt the same thing and he compared it to his Computrainer which reinforced our hypothesis. Just wondering if anyone else has experienced the same thing. Of course, I understand that it really doesn't matter and that precision is more important than accuracy." Michael Post #35

    ----------------------------

    "I am a fellow Power2Max user as well (Campagnolo Type-S) and have had my unit for nearly 7 months like another user above. In my case I am coming from a Powertap PRO+ and my power values have consistently been ~5-7% lower for steady state efforts and 150-200 watts lower for peak sprint values. Admittedly, it took a while to adjust since the ego was suffering from initial confusion but all was well when I finally managed to test both units at the same time on one bike.

    Prior to riding with both units, I was "killing" myself on efforts trying to replicate my Powertap readings. Now all is well with my "fudge" factor. I just needed collect more data from the new power meter."
    Dan Post #36

    ----------------------------

    "I went from SRM to P2M and found between 1.5-2.5% (lower) difference in power, depending on the time being measured across. I now use a rough 2% 'rule of thumb' when comparing back to any SRM power." Nick Post #37

    ----------------------------

  67. #67
    mtbr member
    Reputation:
    Join Date
    Jul 2012
    Posts
    541
    I got my P2M up and running last week. I only did a couple of trail rides with it so far, but the data so far is very interesting to say the least. Tons of hard efforts in the 30 second - 1 minute range, but I barely sustain 220W normalized for 20 minutes. The trails here are tight and twisty, and not a ton of elevation so the claims and descents are short and steep. I guess the power numbers make sense based on the terrain. Here are a couple of pictures of the P2M with Rotor Rex 3 cranks on my Specialized Epic.

    Power2Max MTB Power Meter-img_1226.jpg

    Power2Max MTB Power Meter-img_1225.jpg

  68. #68
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    Thanks to bloodninja for letting me post some of his power data.

    When you first get a power meter I think it's a good idea to just ride with it for a few weeks. As you build up a stock of ride files you'll start to create a picture of your own riding and abilities. Don't get hung up on trying to use training zones or sticking to particular power outputs until you have a good handle on what you can and can't do in terms of power output.

    When you first get a power file of a route that you don't know and haven't ridden the first thing is to try and get a mental picture of what it represents. GPS makes this a lot easier. I like to look at the map with power overlaid as a colour coded line.



    This shows bloodninja's mountain bike ride on 04 April 2015. "First lap was warmup. Second was Lakeview Loop twisty, rooty, and moderately technical singletrack. The third lap was fire roads and some pavement. The last lap was smoother "flowy" singletrack."



    From the map you can see how there are some clear differences. The singletrack sections are twisty with lots of bends, there's a lot of white (0-20 watts which is freewheeling or soft pedalling) and also quite a lot of Red (greater than 450 watts which is sprinting or trying very hard). The middle fireroad/ road section in contrast is more constant with visibly less freewheeling, although still some hard efforts.



    The next thing I like to do is look at an overview of the elevation profile. Here I've zoomed in on just Lap 2 Lakeview Loop.



    There's not a great deal of elevation change or any major climbs. That doesn't mean it's flat though! You can see from the elevation how it's constantly up and down, like a saw blade. That gives an insight into what the power output is likely to be like here. Tight and twisty with constant small rises is unlikely to see a steady state power output. Below the elevation you can see bloodninja's power output. Each time there's an uphill rise there's also a 20 second to 1 minute power spike at 300 to 360 watts.

    This shows a pie chart of the power distribution for just the 10.5 miles of the Lakeview Loop.



    What I look for is the amount of time spent freewheeling or soft pedalling. 0-20 watts is typically freewheeling and anything below 100 watts is soft pedalling. Here there's 23 minutes 12 seconds (33.9%) of the time spent below 100 watts on a 1 hour 2 minute loop. The aim is always to minimise this. If you're not putting down as much power as you're physically able then there's potentially time to be gained.

    On difficult terrain there's not much you can do about having some time below 100 watts. This is where improvements in technical skills and line choices will show up. Equipment choices - tyres, full suspension etc can make a difference too. Fit chunkier tyres with more cornering grip and you may be able to pedal through more corners and accelerate earlier. Dial in the bike's full suspension and you may be able to keep pedalling over the roots or take a more direct line through the obstacles. If you see that time spent below 100 watts reducing thats a sign of progress in your riding.

    At the other end you have the time spent above 450 watts. This was 5 minutes 52 seconds (9.3%) for the Lakeview Loop. This is where you were trying hard and it represents the peaks of the frequent 20 seconds to 1 minute efforts. When you're doing lots of these efforts for several hours it can take it out of you sprinting repeatedly. For pacing offroad this is where the power meter can come in useful. If you have the Garmin display showing with 3 second smoothing you can double check your effort on these rises. 30 seconds or over uphill is long enough that you can usually manage a quick glance at the Garmin. If it's showing too high a number on these short bursts early on you can then back the intensity down to a more sustainable level, saving your energy for later in the ride. Alternatively, if you look down and see the power numbers are too low part way up a rise it's a sign to try harder.

    This shows the summaries for Lap 2 (Lakeview Loop singletrack), Lap 3 (fire road/ tarmac road), Lap 4 (tight singletrack) excluding cool down.



    If you look at your heart rate it gives a good idea of how hard you rode each hour. You went hard on the Lakeview Loop and then the remaining two hours were at a steady pace. Without knowing your plan for the ride that appears to be how it went. If you'd planned to do the entire ride hard then the pacing was way off.

    The most notable thing here is your cadence. There is a big difference between Lap 2, where you were trying hard, and the rest of the ride. For Lap 2 trying hard you averaged 90 rpm cadence for an hour whilst at lower intensities you were only averaging around 82rpm, including on similar terrain during lap 4 for an hour on the tight singletrack at 81rpm. That's a big difference in pedalling cadence which you want to have a think about. I'd do some more rides and see if that pattern continues.

  69. #69
    mtbr member
    Reputation:
    Join Date
    Jul 2012
    Posts
    541
    This is a great analysis and gives me so much to think about. Thank you so much WR304. I test myself from time to time on the Lakeview loop, since it's pretty representative of a Cat 3 race around here. I intended to go 90%+ there and then make the rest of the ride zone 2. If you look on Strava though, you can see that I went for a PR on the Green loop the first time around. I was feeling good after the fire roads, so I figured I'd go for it.

    I think it's pretty common for my cadence to be 90 or higher when I'm trying hard, and 80 or so when I'm pacing myself. I see the same thing on my trainer rides, and my really hard intervals are even over 100.

    I have to give some more thought to the amount of time that I spend coasting or soft pedaling. One of the things that struck me while I was riding was how often I'm in a relatively flat section, feeling like I'm moving pretty fast, but only putting out 90 watts. I can put out 150-180 watts and still recover between the hard efforts, so why not push it a little more on the flats? On the other hand, maybe I should conserve as much energy as possible so that I can go as hard as possible on the climbs where there's more time to gain. I'll definitely be paying attention to the amount of time I spend under 100W, but also avg speed vs NP for the loop. I also expect that I'll make up a little time as my handling improves to where it was last fall. I've only ridden outside a handful of times so far this year.

    The map with color coded power output is great. Is that using Rubitrack? I wish it were available for windows.

  70. #70
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    The colour coded map is from rubiTrack for IOS on iPad. For an easy to use analysis program I think it works really well.

    rubiTrack for iOS by Markus Spoettl
    https://appsto.re/gb/YQNfR.i

    You can have various different map types overlaid. I usually use the Open Street Map overlay but satellite imagery can give a good idea too. Where your ride was in woodland a lot of the offroad riding around here is over farmland. That affects your power output and the pattern of the ride.

    Here's an aerial view of a short section of my ride from today. This is over fields and then along a farm track. The first part is grassy field then you have a farm track, then it turns into singletrack path as it goes through some trees (muddy) before you rejoin the farm track. Because you're tending to follow field boundaries there aren't that many bends.



    I averaged 154 watts for this 1.5 mile section and wasn't going flat out. I've done it far quicker in the past. There's a big section of downhill on farm track where I was freewheeling that I could easily have pedalled.

    There are two short sharp rises where you can see my power jump. The second one in particular is steep on rough rocks. I was in bottom gear sitting right on the nose of the saddle up there.

    Edit:

    Here's the graph of the same section in WKO+ 3.0 with the same parts of the route highlighted. You can see how the power output varies between different parts of the



    To try and give a visual idea of how this appears when riding I found a picture I took of the steep rise on the farm track at the end of this graph. This is where I was in bottom gear (taking the right hand track as it has the fewest loose rocks).

    Last edited by WR304; 04-09-2015 at 12:16 PM.

  71. #71
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    Here are some offroad climbing and descending power graphs from today's ride. It was a nice day but still muddy in places. I did 3 hours (40 miles) on what is quite a hilly route with a mix of off road and road sections.

    This satellite map and WKO+ 3.0 graph shows my power output riding around some fields and then going down a byway descent. This track had large farm tractors on it recently making for a rough surface over their tracks.





    For the first section of the descent I rode on the middle between the ruts at 18.6mph. It was quite rough washboard and the full suspension was doing its job here. There's a steep turn at one point which I took slowly at just 3.7mph before accelerating back up to speed, still staying on the centre section between the ruts. Partway down it was muddy and loose rocks too, muddier than I'd expected where the tractors had churned it up. If you look at the gradient trace on the attached WKO+ 3.0 graph you can see how this was a flatter section. On this section I was picking my way through at low speed (8mph) but pedalling to make sure I wouldn't get the front wheel hung up in the holes or deep mud.

    After that it opens out and I could get off the brakes until the descent flattens off. Once I'd turned off the byway back onto the road there is a short steep road climb and then a road descent immediately afterwards. I've included them as although they aren't offroad sections they appear on the map above.

    This satellite map and WKO+ 3.0 graph shows my power descending a byway on quite a rough surface and then climbing back up the other side.





    Rain water has eroded gulleys across the path on the descent and they're full of gravel so you have to lift the front wheel over them and criss cross from side to side to find the best line. This is where the satellite map can help explain what was going on. I set off confidently on the open section at 17mph, prepared to let the brakes off and the bike run but you can then see where I reached the small wooded part I slowed right down to 4.4mph. Under the trees there was lots of deep mud. I took the dry line but it was right next to a small wall. I was only half pedalling keeping the pedal up high and lifting it back up at mid stroke, not wanting to pedal full circles in case I grounded my pedal on the wall I was that close. After that it opened out again so once past the worst of the eroded gulleys I was back up to 20mph.

    After a long time stuck trying to cross the main road I then began the climb up the other side. This is on a track that has loose rocks on it (similar to the picture in the post before this one). It starts off steep, flattens off mid way up and then steepens again towards the top. I went up here fairly hard, averaging 253 watts for 3 minutes 47 seconds up the 0.5 mile climb. I need to do a proper full gas effort up this climb sometime (My best power output for five minutes this year is 309 watts). I reckon I can do it quicker.

    Just after this climb I was riding some singletrack in the woods and got a muddy section completely wrong, falling off straight into a bramble bush. I was sat there on the ground picking all the thorns out of my arm, hands and side, blood everywhere from the cuts. Some things never change... I got back on rode the rest of the section cleanly and made it round the rest of the ride in one piece.

  72. #72
    mtbr member
    Reputation:
    Join Date
    Jul 2012
    Posts
    541
    WR304, I sure am impressed with what you're able to do with one good leg. Glad you were able to get back up and finish the section after you fell into the bush.

    Your analysis of the ride is great. You really broke down every part of the ride. I want to do that, at least for races and hard training rides, after I spend some time gathering data first. I have a Kindle Fire and PC, so I guess I can't use rubiTrack. Too bad, because that map feature is great.

  73. #73
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    The problem with only having one working leg is that it's a case of either clear a section or fall off. There's no bail out option as my left leg just gives way. I try not to take too many risks but falling off is part of the sport. It's always going to happen sometime. In general I rely on the bike to get me through unscathed. It's amazing how much stuff it can plow through without much rider input.

    I was feeling a bit sore to begin with on today's ride so I stopped now and then to take some pictures on the way out. The first part of the ride was fairly low key and then I did some higher intensity efforts on the way back.

    Being able to represent power data in a way that is useful, so that you can take that data, critique it and improve your riding as a result isn't always easy to describe in words. What I thought I'd do would be to take photos of particular sections and then put some notes on the pictures.

    This picture shows a section of byway with a river crossing. The green line and arrows show my direction of travel. I came down the hill across the bridge, weaved between the concrete bollards and then accelerated away afterwards.



    A view over the bridge showing the bollards and opposite bank:



    This is the WKO+ 3.0 graph with the same notes so that you can see my power output at the highlighted points in the photograph. I was trying hard throughout here.



    If you look at the photo and the green line the first thing to note are my line choices. That green line twists and turns several times. On the opposite bank I came right down towards the river, which is deep loose gravel, before turning across towards the bridge. This shows in my power output and speed. Where I had been doing 21 mph I was now braking, 0 watts and down to 8mph. I put some pedal strokes in to get up and over the bridge at 182 watts and 8mph before another right - left turn between the bollards at 0 watts at 5.5mph. On the exit I was back up to full power heading towards the gravel slope away from the river crossing.

    This is where the photo and power data together hopefully shows where there is room for improvement through line choice. You can see from the power data that I was slow approaching the bridge, slow over it and slow on the bridge exit too. As soon as you see all that time at 0 watts, turning slowly on loose gravel and weaving between bollards at 5.5mph that raises an immediate red flag. Is this the best way to ride this bridge? Probably not.

    On a mountain bike good line choice is everything. In the bridge photos above you can see the opposite bank. There's a second higher track that I didn't ride today. This is hardpacked dirt, not loose gravel, so will have higher grip. It also gives a straight line onto the bridge, cutting out the turns. This should be a faster entry line. On the exit of the bridge nearest to the camera, instead of turning right then left between bollards it is possible to go to the far left side of the small bush, giving a straight line without needing to turn between the bollards. You can see the path as the dark mark in the grass on the photo. By using that alternative line it should be possible to save several seconds on just this one bridge.

    This picture shows a section of bridleway on a rocky farm track. It starts off slightly downhill, there is a short sharp 14% gradient rise and then the track continues gradually uphill at around 3.5% gradient. Out of picture there is then a descent down to another farm gate.



    This is the WKO+ 3.0 graph for this section.



    What this tries to show is how power output responds to the terrain. I set off freewheeling from where I had taken the photo, I then try quite hard at 15mph and 241 watts, a short pause in power weaving between puddles and then I blast up the short steep rise. Here my power output averages 325 watts at 8.7mph on the steepest section, although it's near the end of the ride and it feels harder than that. I then keep working hard up the 3.5% gradient slope, 179 watts at 11mph until I reach the top and begin the descent to the gate.

    From the power trace the main thing to look at is my power output on the 3.5% gradient slope. You can see how it isn't a straight line, instead my power output is gradually dropping throughout as I near the top. That's a bit where I could have done better. That drop in power output will show on the display as you're riding. I should have responded to this drop in power by upping the pace but I didn't. I had my thumb on the trigger shifter but didn't press it.

    My explanation for this is the short sharp power burst at the bottom. It doesn't look much but if you put a really hard effort in the result is that you then have to recover from that effort at some point. Sometimes showing restraint on the short sprints can pay off with higher power outputs later on. Here for example if I'd gone up the steep section a little easier I might have then felt able to ride the following 3.5% gradient slope at a higher power output than I did today. It's all about parcelling out your effort for maximum effectiveness.

    These two pictures don't have any power data attached. I've included them as they're representative of the farm tracks that a lot of my riding is on. There are ruts from the farm vehicles which are usually deep and full of water. You then have a central section that the motocross bikes and mountain bikes use. The motocross bikes in particular create a third rut. This is why I like Specialized Ground Control tyres as they work well on this type of mud, whilst still performing on hard pack gravel and rocks too.



    This picture shows a bridleway path around a field boundary. It's dried mud, full of horse hoof prints and tractor tracks. Riding on this stuff is rough enough to get the bingo wings flapping and dentures loosened. There aren't any large bumps but it's a constant beating and takes some effort to keep going. On this section today I averaged 201 watts for just 12 mph speed!


  74. #74
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    My bike has been making nasty creaking noises for the last month or so, whilst pedalling in just the 23T granny ring originally but increasingly in the 33T middle ring also. There was no creaking in the outer 44T chainring. It started off intermittent but by today it was sounding horrendous.

    Despite taking the crank off, checking all the chainring bolts (at the end of March they seemed fully tight), trying a different rear wheel (in case it was the freehub or cassette) etc I couldn't track it down.

    It was sounding so bad today that when I got home I decided to check the chainring bolts again. This time when I went to check the alloy chainring bolts holding the two outer chainrings together the head of the first chainring bolt sheared off immediately with only minimal pressure! I carefully unfastened the other three chainring bolts. Of those two appeared fine but the third was close to breaking too. This bolt had a long split running round it and the head was only loosely attached. That explained why I'd been getting creaking. Two out of four of the alloy chainring bolts had failed.



    The reason that these bolts were what was causing creaking in the granny ring is that on my Power2Max triple chainset the granny ring bolts onto a carrier that is in turn bolted in place by the same chainring bolts that hold the two outer chainrings on. All the torque from the granny ring goes into the carrier and those four bolts.

    I've replaced the four alloy bolts with steel bolts now. Hopefully that will have cured the creaking.

  75. #75
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    There I was thinking I'd finally solved the creaking issue by changing the chainring bolts yesterday. Nope. First climb of the day today and the bike is creaking as loudly as ever.

    I'll have to keep searching.

  76. #76
    mtbr member
    Reputation:
    Join Date
    Jul 2012
    Posts
    541
    Sorry to hear that it didn't fix it WR304. Trying to track down creaking is the worst. Did you eliminate seatpost and suspension linkage as possible causes?

    That reminds me... I think due to the type of aluminum used in the Rotor no q rings, if there's even the slightest bit of grit on my chain it makes a sound like my drivetrain is getting chewed up. It makes me feel the need to clean my chain thoroughly after every single outdoor ride...which I guess really isn't a bad thing.

  77. #77
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    With my custom crank it could potentially be the lockring thread holding the spider on or even the crank spindle itself that is creaking. You then have all the usual problem areas bottom bracket, suspension, saddle etc

    Today it was sounding bad in both the granny ring and middle ring, but I was also getting occasional creaks when hitting bumps. It's not consistent, sometimes I can be putting a lot of effort in and the bike isn't creaking. Next thing I'm soft pedalling and it's creaking like mad.

    When riding it all feels fine though. Apart from the noise the bike is working normally and I've been going well fitness wise, setting some new climbing personal bests and also power personal bests at the weekend.

  78. #78
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    I tried a different crank today (instead of the power meter crank) and the bike was creaking as badly as ever. The creaking wasn't from the power meter crank. It's a really dry "cracking" sound of creak. A carbon fibre creaking sound that comes and goes when I'm pedalling.

    So far I've replaced the seatpost, seatpost collar, saddle, pedals, and bottom bracket with brand new parts, greased the SRAM X0 rear derailleur clutch, tried using a different crank, tried an entire different rear wheel with no joy.

    There isn't a great deal left. It's looking like maybe there could be something going on with the pressfit carbon fibre bottom bracket shell (this bike is on its fifth press fit bottom bracket) or maybe a rear suspension pivot bearing where it is pressed into the carbon frame (this bike is on its third set of pivot bearings).

  79. #79
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    My bike has been in and out of the bike shop several times to see if they could find this creak. As I only have the one bike I've been riding it in between. Although it was noisy the bike was riding fine.

    Yesterday I'd been out on the club ride. The bike had been relatively quiet all ride. I was on the way home through town when I rolled up to some traffic lights. From an almost stationary start (with both feet on the pedals) I put in my best 20 second sprint of 2015, 565 watts maximum power and an average of 462 watts for 20 seconds.



    Unfortunately laying down that "awesome" sprint was more than the bike could handle. It's only a few minutes home after that but the creaking following that sprint was horrendous!

    When I got home I could see why. Something in the lower rear suspension pivot bearings has broken and failed completely. In the picture below the large gold allen bolt bolts through and secures the bearings. This is normally recessed and flush with the edge of the swingarm. You can see the ring of dirt where its normal position would be but it is now protruding from the frame. There's a ton of play in the rear triangle. Rock the rear wheel by hand and those lower pivots are wobbling freely. Not good.

    Ironically enough it was booked in for all the rear suspension pivot bearings to be replaced tomorrow anyway.


  80. #80
    mtbr member
    Reputation:
    Join Date
    Jul 2012
    Posts
    541
    Congrats on the PR! I hope that the bearing overhaul takes care of your creaking issue finally.

  81. #81
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    I got my bike back from the bike shop today. Apparently all the rear suspension pivot bearings were seized. The whole lot, s-link bearings, horst link pivot bearings and the main swingarm bearings were stuck. They were new from October 2014.

    The large gold aluminium bolt holding the main bearings together hadn't broken but the threads were stripped so that bolt had to be replaced too.

    Fortunately the new bearings pressed into place ok so the frame seems undamaged. I'm hoping that will have cured the creaking now!

  82. #82
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    Changing the suspension pivot bearings didn't make any difference to the creaking when pedalling. The bike has been working ok but it's still noisy.

    I ordered a bbinfinite bottom bracket from the US to try instead of the Praxis bottom bracket. Bbinfinite bottom brackets are pressfit. They're supposed to be a very precise fit to eliminate creaking:

    http://bbinfinite.com/index.php?route=common/home

    Installation video:

    https://www.youtube.com/watch?v=DfGtZhqGPoc

    Here's a picture of the PF30 Shimano axle bbinfinite bottom bracket fitted to my Epic. It certainly looks good, as though it's an original part of the frame.



    I haven't tried it yet as one of the pinch bolt threads in my left hand crank stripped. I had to get the threads helicoiled. The custom left hand crank spline hole doesn't look great either. It looks like there might be some play between the left hand crank and axle, due to it not having been clamped firmly in place, which could potentially be causing creaking.


  83. #83
    mtbr member
    Reputation:
    Join Date
    Jul 2012
    Posts
    541
    I hope the bbinfinite bottom bracket works out for you. A friend of mine had trouble with a creaking BB and used two-part epoxy to attach the BB to his 2014 Epic. It's worked well for him for over a year now.

    In other news...I installed my road P2M over the weekend. One ride with it so far, this morning, and the first thing I notice is how I make less power in the drops than on the hoods. It's probably a combination of fit and getting used to the position since I never owned a road bike before, but I don't plan on doing any serious road racing so I don't care much.

    Power2Max MTB Power Meter-img_1346.jpgPower2Max MTB Power Meter-img_1347.jpg

  84. #84
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    The bbinfinite bottom bracket comes with loctite included as part of the kit. The instructions for removing the bbinfinite bottom bracket - I kid you not - require ear and eye protection and an air hammer. With a carbon fibre frame that's a frightening thought if it goes wrong!

    https://www.youtube.com/watch?v=m1Sunq3Qz-w

    The idea is that the bottom bracket module stays in the frame, more or less permanently, whilst you just replace the individual bearings as needed.

    I had a demo bike to try a few weeks ago, a 2015 Specialized Epic Elite World Cup. I had my own left hand crank and shortener fitted in order to ride it. When removing the original left hand crank the SRAM PF30 plastic bottom bracket cup came out at the same time. It was such a loose fit that you could push the bottom bracket cup back into the frame by hand. It didn't creak whilst riding but was hardly ideal.





    Apparently your power output is affected by your riding position. As you crouch more and more forwards it closes your hip angle. Sitting upright, such as on a mountain bike, ought to see you putting out most power, and then as you move down towards a low time trial bike position on aero bars you put out the least power. It's the tradeoff for being more aerodynamic.

    It's part of why you often see it recommended to train in the position you race in, so that you're as effective as you can be on your primary bike. If you were going to be doing a lot of time trialling for example then you'd want to spend plenty of time on the time trial bike, in order to adapt to the position and reduce this power loss as much as possible.

  85. #85
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    On the club ride today one of my friend's was saying he wanted to go hard up one of the local climbs. One of his friend's had been giving him stick about having beaten his climbing time a few days earlier so this was payback! Strava is serious business sometimes.

    I was dropped but still did my best 20 minutes of the year (259 watts for 20 minutes , 3.90w/kg). I set a personal best for the climb too, a minute quicker than I'd managed up there before. I was quite happy with that.

    That was all well and good but later in the ride today my front shifting was all over the place and the chain kept shifting off the outside of the big ring. When I got home I discovered why.

    The bbinfinite bottom bracket had walked out of the frame. My cranks had shifted inwards towards the frame so the chainrings were out of alignment. The inside chainring was catching on the frame and had cut a gouge in it.



    This bottom bracket looks like it was a seriously bad idea. The bbinfinite bottom bracket is a single unit. It doesn't press together. There's a flange on the non drive side but nothing on the drive side, no flange or retaining mechanism at all. It relies purely on a tight fit and blue loctite between the frame and bottom bracket to stay in place.



    This 2012 Specialized Epic carbon frame with a Pressfit 30 bottom bracket shell has done 1,408 hours riding / 20,665 miles. It's had six bottom brackets fitted (original SRAM PF30, SRAM PF30 to BSA, Chris King PF30, Praxis, Praxis, bbinfinite). The bottom bracket shell might not be a tight enough fit anymore. You can see the blue loctite on the bottom bracket where it was applied when being fitted. Even so it came apart after such a short time. It had only done just over 10 hours riding since being fitted.

    This article has some more pictures.

    http://www.bikerumor.com/2014/05/16/...t-performance/

    Changing the bottom bracket made no difference to the creaking either. As this bottom bracket is loose in the frame it didn't prove anything either way.

    Update: The bike shop hammered the bbinfinite bottom bracket straight out this morning and put my previous Praxis bottom bracket back in.

    It wasn't particularly tight in the frame fortunately.
    Last edited by WR304; 08-12-2015 at 05:22 AM.

  86. #86
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    I've got a Garmin Edge 520 to replace my Garmin Edge 500 now.



    The Garmin Edge 520 paired straight away with the Bontrager ANT+ speed sensor and Power2Max power meter on my bike. The calibration figure for the Power2Max power meter appears as the same on both the Garmin Edge 500 and Garmin Edge 520 and I have the same manual wheel circumference entered for the speed sensor.

    Riding with it for the first time today the Garmin Edge 520 worked happily with the Power2Max. There were no sensor dropouts, spikes or issues anywhere in the 3 hour 52 minute ride so it all looks good so far.

  87. #87
    mtbr member
    Reputation:
    Join Date
    Nov 2009
    Posts
    699

    Power2Max MTB Power Meter

    My edge 500 used to ask if I wanted to calibrate when it detected my quarq but the 520 doesn't. Any idea how to get it to?

    Edit: called garmin today and they said it doesn't do that anymore. Can suggest it at their website http://www8.garmin.com/contactUs/ideas/
    Last edited by litany; 09-10-2015 at 10:28 AM.

  88. #88
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    Garmin Edge 520 Settings

    The Garmin Edge 520 has different activity profiles. I have two setup. One is called Epic for my mountain bike and one is called Turbo Trainer for indoors riding. These are the settings and data fields for my mountain bike:

    Activity Profile "Epic"

    Data Screens:
    Screen 1: 3 Fields (my normal riding screen)
    Field 1: Power 3s
    Field 2: Speed
    Field 3: Time

    Screen 2: 10 Fields (my summary overview screen to look at when riding)
    Field 1: Time
    Field 2: Distance
    Field 3: Avg Speed
    Field 4: Avg Power
    Field 5: Avg Cadence
    Field 6: Totl Ascent
    Field 7: Elapsed Time
    Field 8: Avg Balance
    Field 9: IF (Intensity Factor)
    Field 10: NP (Normalized Power)

    Screen 3: 4 Fields (Misc items that I may want to look at infrequently)
    Field 1: Time of Day
    Field 2: Temperature
    Field 3: Battery
    Field 4: GPS Accuracy

    Screen 4+5: Off

    Map Screen: None - On

    Compass Screen - Off
    Elevation Screen - Off
    Lap Summary Screen - Off
    Virtual Partner Screen - Off
    Cycling Dynamics Screen - Off

    GPS Mode: GPS+ GLONASS

    Map
    Orientation: Track Up
    Auto Zoom: Off
    Guide Text: When Navigating

    Alerts
    All turned off

    Auto Features
    Auto Lap: Off
    Auto Pause: Off
    Auto Sleep: Off
    Auto Scroll: Off

    Start Notice: Off

    Sensors:
    I have an Ant+ Speed sensor with manual wheel circumference and power meter paired.

    Bluetooth: Off

    System:
    Display: Brightness 40%
    Backlight Timeout: 15 seconds
    Color Mode: Day
    Screen Capture (usually Off)

    Data Recording
    Recording Interval :1 sec
    Cadence Averaging: Do Not Include Zeros
    Power Averaging: Include Zeros

  89. #89
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    Garmin Edge 520 Power Meter Settings and Notes

    If you have a power meter connected there are a few other screens to go through also. With a Garmin Edge 500 it would always come up with a pop up message "power meter detected do you want to calibrate" y/n (set the zero offset) screen when first turned on.

    The Garmin Edge 520 currently doesn't have this prompt. You can still manually calibrate (set the zero offset) by pressing the up arrow once to go to the status screen. If the power meter is connected you will see a calibrate option. Select that and it should give you a success message as pictured below. Under sensors you can also go to about and look at what details there are for it. With a Power2Max classic power meter this shows the battery level, firmware version etc for the power meter onscreen.



    Different types of power meter will have different options and report different zero offset values here. With a Power2Max whenever you freewheel for a few seconds whilst riding it will automatically reset the zero offset by itself. Doing a manual zero offset before starting isn't that critical so long as you freewheel from time to time during the ride.

    If you have a Quarq then it's important to remember to manually set the zero offset at the beginning of the ride. To reset the zero offset on a Quarq whilst actually riding you have to backpedal five times otherwise. One of my friend's has a new model Quarq on his road bike. He did a road race a few months ago where the zero offset wasn't set correctly (he did the zero offset calibration with one foot still clipped into the pedal just before the start). The entire race file was garbage as a result. All the power numbers were way off.

    If you have the Powertap P1 pedals the Garmin Edge 520, along with the Garmin Edge 1000, still has the incorrect crank length issue. This is where the crank length setting defaults to 172.5mm with no option to change it. See this thread:

    https://forums.garmin.com/showthread...rTap-P1-Pedals

    Setting FTP and Power Zones
    This is under Menu - My Stats. There is a seperate section called FTP here, which you should ignore and leave turned off!

    Where you actually have to go is keep scrolling down in My Stats beneath User Profile to the Training Zones section. Under Training Zones select Power Zones. At the top is where you manually enter your FTP figure. For consistency this should be whatever you use in other programs such as WKO+ 3.0, Golden Cheetah, Strava etc.

    FTP: enter your own value
    Based On: Watts
    Minimum: 0w

    I have the power zones set manually to match the six Coggan power zones in WKO+ 3.0.

    http://home.trainingpeaks.com/blog/a...raining-levels

    In order to make them match I first edited Zone 7 so that it wouldn't be used. Enter a massive number in there that you will never reach, 5,000 watts say and then make Zone 6 limit just below it. The other zones can now be set to match.

    Once that is done the metrics such as IF, TSS, w/kg time in power zones etc should be very close to what you will see once the ride is loaded into your preferred program.

  90. #90
    mtbr member
    Reputation:
    Join Date
    Feb 2009
    Posts
    987
    Given all my recent experience with P1s on my road bike I think I have to switch from my Stages on the MTB. P2M seems to be the only option available (SRM not an option and Quarq is only single front).

    The only aspect that is keeping me from ordering a crank set is that both my MTB frames are BB 89.5. If P2M I want to go with Rex 1.2.

    According to my own web research Rotor's 4130 BB is not really durable. Race Face seems to offer a more durable alterntive, but you would need check spacing to get the chain line correct. Are there any experiences here? With either BB? Enduro bearings seems to offer a more durable option but I can't find any in Europe.

    Are those Rex 1 easy to swap? Would you damage the bearings easily by frequent de- and installations?

  91. #91
    mtbr member
    Reputation:
    Join Date
    Jan 2008
    Posts
    973
    Why is SRM not an option? Also, you can still find new 2x Quarq - i've seen more bb30 than gxp though.

  92. #92
    mtbr member
    Reputation:
    Join Date
    Feb 2009
    Posts
    987
    Mmmm .... SRM is simply twice as expensive. Therefore simply not option. In particular since I do not buy into the "gold standard" argument. And you can't even Swap batteries yourself. And you're limited to BCD 120/80. Not an option in the Alps.

    Quarq 2x10 ... I simply do not want to buy a phased out product. Though this is just hyothetical because you can't get one here.

    But this thread is about P2M ....

  93. #93
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    Quote Originally Posted by quax View Post
    Mmmm .... SRM is simply twice as expensive. Therefore simply not option. In particular since I do not buy into the "gold standard" argument. And you can't even Swap batteries yourself. And you're limited to BCD 120/80. Not an option in the Alps.

    Quarq 2x10 ... I simply do not want to buy a phased out product. Though this is just hyothetical because you can't get one here.

    But this thread is about P2M ....
    The 2x10 Quarq power meters were 120/80mm BCD too. The smallest inner chainring you could fit was 26 teeth.

    In terms of Power2Max their current double chainring spiders are 110/60mm BCD. It's possible to fit as small as a 22 tooth inner chainring if needed.

    It seems to me that going for a Rotor Rex 3 Power2Max in a double chainring (24mm diameter axle) would probably work better with your current frames. There shouldn't be an issue swapping that between bikes repeatedly as it will come out of the bottom bracket easily. The preload nut is alloy.

    http://www.power2max.de/europe/en/Pr...tor-rex-3-mtb/

    The Rotor Rex 1 crank uses a 30mm diameter axle. A BB89.5 bottom bracket frame is really designed for a 24mm diameter axle crank. Shoe horning a 30mm diameter axle into the same space that was intended for a 24mm diameter axle is going to mean compromising on bearing size and bearing life.

  94. #94
    mtbr member
    Reputation:
    Join Date
    Feb 2009
    Posts
    987
    The ball size in the Rotor 4130 bearings seems to be the same as in BB30 bearings. The cups themselves work as races as well, so there's enough space to make it work. Rotor's BBs are simply of crappy quality. This is at lease the information I could find.

    As already alluded to above there are alternatives. Race Face for example:

    Race Face

    Same story regarding ball bearing size. No difference to BB30. From what I could gather this BB seems to hold up pretty well. But I couldn't find any reports on using it with a Rotor crankset. 4130 comes with plastic washers. Are these required for the Race Face BB too? Can you get them separately? What other spacers are required.

    I was just wondering if anyone has already gone through this exercise.

  95. #95
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    There are so many different bottom bracket sizes and variations nowadays that it's crazy.

    The Rotor 4130 30mm pressfit bottom brackets get terrible reviews. I haven't seen much that's complimentary about them.

    This weightweenies thread on replacing and upgrading the Rotor 4130 stock bearings is worth a look through. It lists some other alternatives and options that may work better for the same size. Apparently a Ceramic Speed bottom bracket that will fit is coming out September 2015 also.

    http://weightweenies.starbike.com/fo...p?f=3&t=133419

    From looking around the Race Face Cinch (30mm diameter axle) bottom brackets come in two types. The BSA threaded outboard version of the Cinch bottom bracket uses the same bearing size as BB30/PF30 42x30x7mm size "6806". With that you could simply press out the old bearing and fit high quality new ones of your choice. That would be fine if you could use that.

    The BB92 pressfit version of the Race Face Cinch bottom bracket uses a custom bearing however. It says it uses the same size ball bearings as a 6806 bearing but they've had to compromise to get it to fit. There's some discussion of the Race Face Cinch bottom brackets in the comments beneath this Pinkbike article. (User "Clapforcanada" in the Pinkbike comments appears to be a Race Face employee).

    "I've been using this RaceFace turbine cinch. It is stiff However my bike is only compatible with BB92, the BB cup does not fit inside the frame. The cinch bottom bracket is horrible. It has more drag and creaking noise. I replaced it twice it similar problem occurred after 3 months. I'll stick with my XX1 chainset for now." Rave81

    http://www.pinkbike.com/news/race-fa...view-2014.html

    In terms of 30mm crank spindle spacers these should be easy to source cheaply. You don't need specific ones for a particular brand. They are available in many different widths (0.5mm, 1.0mm, 1.5mm etc) so you can space the crank exactly as needed. Do a search for "BB30 Spacer" to find the parts you need online.

    Here's a UK seller selling the Wheels Manufacturing 30mm BB30 spacers £2.49 GBP with free shipping. This would go to Germany without any added taxes:

    http://www.ebay.co.uk/itm/Wheels-Man...item25ab441f98

    .

  96. #96
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    When you first create a new interval Workout for the Garmin Edge 520 this has to be done via the Garmin Connect website. Where the Garmin Edge 500 had the option to create and edit workouts on the device itself this feature has been removed from the Garmin Edge 520. All you can do is run, preview or delete workouts.

    In order to create an interval Workout with multiple steps open Garmin Connect in a web browser on your computer, click on the Menu symbol at the top left and select Workouts from the bottom of the list. You then select "Create workout" and begin adding steps. There is a limit on the number of steps that you can have in an individual workout. If you are doing multiple intervals you would nest the steps, so that they are repeated for the correct number of times.

    This picture shows a 3x9 minute Under Over interval session in Garmin Connect. There are 3 9 minute intervals with a 6 minute recovery period between each one. Each 9 minute interval consists of 2 minutes Under, 1 Minute Over, 2 Minutes Under, 1 Minute Over, 2 Minutes Under, 1 Minute Over.

    You can put target zones in but I prefer to just use duration without any target zones in Garmin workouts. This avoids any pop up out of zone warnings appearing when doing the intervals.



    Once you are happy with the workout format send it to your device. In order to start a workout go to Menu - Training - Workouts - "workout name" and select Do Workout. The workout is now ready to begin. When you press the Start/Stop button the Garmin will go through the workout steps in order.

    If you decide to skip a workout step press the Lap button once and it will move onto the next step in the workout instead. Each time you press the Lap button it will advance an additional step.

    When the workout finishes the timer stops immediately. You'll see a Workout Complete notice and the Red band will appear around the outside of the screen. If you're outdoors and still riding don't forget to press the Start/Stop button at this point, in order to restart the timer and continue recording the rest of the ride!

    When actually trying to ride a workout there are some differences from the Garmin Edge 500. The Garmin Edge 500 had a dedicated Workout display screen. On this screen you could add a few Data fields of your choice, so that you were able to look at the information you were interested in. It wasn't amazing but was enough to get the session done.



    The Garmin Edge 520 has a dedicated Workout display screen too. It has some big problems though. The main one is that you can't add your own data fields, making it fairly useless. If you have no target set it only displays speed. If you have a target zone it displays the zone onscreen instead of speed.

    Along with this if you have target zones enabled the problem is that if you go outside the zone a warning message appears. This was bad enough on the Garmin Edge 500 (a box right in the middle of the screen) but on the Garmin Edge 520 there is a massive black box covering half the screen if you're out of zone. It makes it impossible to read the display and stays there for several seconds at a time. I want to be able to see the display as much as possible. By creating a workout with no target zones in the file it avoids the warning messages.



    The dedicated Workout screen on the Garmin is terrible and basically unusable. Fortunately there is a workaround. You can make a custom data screen that will show you most of the information needed. This wasn't present on the Garmin Edge 500 but with the Garmin Edge 520 you can choose to add a data field called Workouts - Time To Go onto a normal riding screen. This gives you the countdown timer for each workout step on a normal riding screen, allowing you to add your own choice of data fields alongside.

    For my intervals screen today I had Power 3 second average as the top field, Time to Go as the middle field, and then Power - Lap as the lower field. As soon as you begin the workout use the arrow keys to scroll from the default Workout screen to the new custom one. Power 3 second average is what I ride to, Time to Go shows how long the step will last and Power - Lap shows the average power for the interval step that I'm riding. Bear in mind that when each step begins you get a message partially covering the bottom of the screen so the most important fields need to be at the top.



    Here is a close up graph showing the first 9 minute Under Over interval of the three in WKO+ 3.0. The graph has no smoothing. The aim with Under Over intervals is to be able to lift your pace, recover whilst still trying hard and then lift your pace again. It is intended to help you deal with frequent changes of intensity when riding. It isn't simply going as hard as you can at one pace for 9 minutes at a time. I was trying to hold around 230 watts for the 2 Minute Under sections (96% FTP) and then hold over 260 watts (108% FTP) for the 1 Minute Over sections.

    The actual power data recorded by the Garmin Edge 520 with my Power2Max power meter looks just like it did with the Garmin Edge 500. You can see how even though I was trying to ride at a constant effort on a road there is still constant variation in power output. When riding it's helpful to have power displayed on the head unit with smoothing, rather than instant power. I usually use 3 second power, it makes the display less jumpy and easier to pace with.

    Riding outdoors you have to be careful with route choice to not get held up. Ideally you want a nice straight road with no junctions or obstacles. During this interval I had to slow down for a junction and then straight afterwards met some oncoming horses so had to slow down again. As soon as you start being held up it drags down your average power.

    Interval 1 wasn't as bad as interval 3. A tractor decided to pass me whilst I was partway through the interval. I was doing 21mph and he was only going 1 or 2mph faster. I had to ease off to let him complete the pass, and then of course I'm in the slipstream so not putting any effort in! As I was trying to stick to a set wattage I wound up braking to let him get a decent gap in front before continuing.

  97. #97
    mtbr member
    Reputation:
    Join Date
    Feb 2009
    Posts
    987
    Still pondering the move to P2M ... here's a quick comparision of weights (PF92 frame assumed). Actually not too much a difference given the price difference. And I don't think I would notice the additional stiffness of a 30 mm axle. I'm really leaning towards Rex 3.2 now.

    Though I probably wait until next spring. Who knows if prices drop further. Or other options show up (though I doubt this, unfortunately not a lot of development going on for MTB PMs). And winter is here mainly running, road bike and Kickr. To much snow for offroad/dirt road riding. So there is no immediate need to upgrade.


  98. #98
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    One of my friend's is getting some Powertap P1 pedals very soon. Whilst reading up on the Powertap P1 battery life and recommended batteries I came across a thread where someone had posted an x-y plot from Golden Cheetah showing how their Left / Right Pedal balance changed with power output.

    Post #89:
    Stages Power Meters - A Worthless Product (Page 4): Triathlon Forum: Slowtwitch Forums

    Powertap P1 battery life:
    Power tap P1 - what are your thoughts after first weeks: Triathlon Forum: Slowtwitch Forums

    The x-y plot was made in Golden Cheetah.

    To make your own load a ride activity with some representative hard efforts in Golden Cheetah. At the top right of the screen just above the graph there is a tiny (and I mean tiny! ) three line menu option. Click on this Select - Add Chart and choose 2d plot from the list. The plot settings that I used:

    X Axis - Power,
    Y Axis - L/R Balance,
    Smooth 8,
    Ignore Zero - Ticked
    Show Grid - Ticked
    Frame Intervals - Unticked
    Compare Mode - All Activities/ Activities
    Trend Line - Auto

    Here's the x-y plot from Golden Cheetah showing how my power balance changes with power output. The turqoise colour shows the right leg contribution and the red colour shows the left leg contribution.



    At low levels of effort the imbalance is largest. At 100 watts my right leg is shown as doing around 90% of the work with the Left left leg doing 10%. The Power2Max doesn't do true Left - Right power. Some of what shows as left leg power on this plot is actually where I'm pulling up with the right leg during the pedal stroke. Even so, as I try harder my power output becomes gradually more even. At 500 watts my right leg is shown as doing around 65% of the work with the left leg doing 35%.

    If you're pedalling normally with two legs your power balance in an x-y plot like this ought to be a lot closer to 50/50, with far less pronounced shifts in balance than shown here. If the two coloured lines overlap on this x-y plot then each leg would be contributing equally.

  99. #99
    mtbr member
    Reputation:
    Join Date
    Feb 2009
    Posts
    987
    My asymmetry is not as pronounced. Therfore, the GC L/R plot is just one big data cloud. I wish one could plot only the actual measurement, e.g. just the L/R Balance value.

    Here is yesterday's easy tempo road ride with my P1s:




  100. #100
    mtbr member
    Reputation: WR304's Avatar
    Join Date
    Jul 2004
    Posts
    4,929
    A ride with really hard efforts across a range of durations (the ride I used was a 4 hour club ride full of sprints and 5 to 30 minutes flat out efforts pedalling at maximum effort) ought to show pedalling balance changes up most.

    With an x-y plot like this removing the zero watt values, along with applying some smoothing and adding a trend line, should make it clearer.

    Looking at the x-y plot you posted from the Powertap P1 pedals, along with the ride graph, there is a trend there. I've edited the x-y plot picture slightly, by removing the zero watt points, clearing up the outlying points and adding a red trend line.



    (A point showing 55 on this x-y plot would be 55% Left leg and 45% Right leg balance)

    It appears to me that you favour your Left leg by a bit at lower intensities. There's a sustained bias towards the Left leg visible in your x-y plot, maybe as much as 55% Left and 45% Right at 150 to 200 watts. As the power output increases past 250 watts towards 400 watts, where you're trying hard, the power output becomes balanced and shifts back towards even power output between legs.

    Edit:
    Golden Cheetah has an interesting feature when it comes to Left/Right pedalling balance. It doesn't tell you specifically which is Left and which is Right leg! After some rapid editing here is my guide to how you identify which leg is which.

    In the Golden Cheetah summary screens you only get a single number such as Left/Right Balance (%): 18.0. It doesn't say which leg this is. As I have such a heavy Right leg bias I know that this low number must represent the work done by the Left leg. i.e. 82% Right Leg / 18% Left leg. If you only have minor leg imbalances it isn't easy to identify which leg is which in Golden Cheetah.

    Here are some screenshots showing different leg imbalances in the Golden Cheetah graph view. The highlighted shaded red line at the bottom of each picture is the power balance. On the right hand side you can see what a heavy Right leg imbalance looks like. This is from one of my rides. The Right leg imbalance is shown by how all the points are below the 50 middle point of the graph, indicating that the Right leg is doing more work than the Left leg.

    On the left hand side you can see what a minor Left leg imbalance looks like. This is from Quax's graph above. There is far less of an imbalance here but you can see how the majority of the shaded red is above the 50 middle point of the graph, indicating that the Left leg is doing more work than the Right leg.




    Dcrainmaker has announced that Garmin is releasing the new firmware updates required to use the Powertap P1 pedals with their Edge 1000 and Edge 520 this week:

    "Finally, for those on the FR920XT, there’s now a beta firmware update out that allows adjusting crank length for non-Vector power meters (needed for the P1). Additionally, the Edge 1000 firmware update went out this past week. And then final Edge 520 firmware update should be out any day now according to Garmin. All other Garmin devices are already compatible." dcrainmaker

    Interbike Power Meter Tidbits Roundup: Pioneer, Xpedo, WatTeam, PowerTap | DC Rainmaker
    Last edited by WR304; 09-28-2015 at 11:07 AM.

Page 1 of 3 123 LastLast

Similar Threads

  1. Power Meter Importance
    By aschoks in forum XC Racing and Training
    Replies: 3
    Last Post: 05-20-2013, 07:11 AM
  2. Power Meter or not?
    By carlostruco in forum XC Racing and Training
    Replies: 22
    Last Post: 09-08-2012, 04:44 PM
  3. Calculating power and power meter operation
    By dstorjoh in forum XC Racing and Training
    Replies: 5
    Last Post: 07-23-2012, 08:35 AM
  4. MTB power meter thread.
    By Johnny K in forum XC Racing and Training
    Replies: 30
    Last Post: 05-20-2012, 03:02 PM
  5. 705 with a Power Meter on one bike
    By the mayor in forum GPS, HRM and Bike Computer
    Replies: 3
    Last Post: 04-10-2011, 02:49 PM

Members who have read this thread: 69

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •