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  1. #1
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    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
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    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
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    Paula Newby Fraser use to ride a set of funky cranks like does on her Triathlon bike..

  4. #4
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    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
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    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
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    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 bull****.

  7. #7
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    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
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    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 **** 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
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    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
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    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
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    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
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    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 **** 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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    Power2Max MTB Power Meter

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

  24. #24
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    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
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    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 05:41 AM.

  26. #26
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    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
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    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
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    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
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    I wish PM manufactures would get on the ball with the X11 stuff. The power2max setup looks nice.
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  30. #30
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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.

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