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Thread: PowerTap Disc

  1. #1
    LW Coaching
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    PowerTap Disc

    I got one!

    Here are pictures of it. I can't ride it today but I'll be on it tomorrow.

  2. #2
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    Sweet!

    No excuses for missing training logging now!

  3. #3
    LMN
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    Let me know how the water sealing works.


    Power taps and wet haven't exactly worked well in the past. They claim to have fixed it but that remains to be seen.

  4. #4
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    so these are now available for purchase? awesome. a few weeks ago they said they were still on the production line.....

  5. #5
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    Saris can't build them fast enough. I work at American Classic, and we are building on them!! If you want a Disc Brake 2.4 Powertap we can build them 26" or 29", 32 hole only. <br> LMN- the computer seal is VERY tight on these. We double check every PT we ship to ensure the seal is good. No problems so far for us!

    <a href="http://s106.photobucket.com/albums/m266/threadoflifephoto/?action=view&current=IMG00159.jpg" target="_blank"><img src="http://i106.photobucket.com/albums/m266/threadoflifephoto/IMG00159.jpg" border="0" alt="AC built Powertap Disc"></a>
    Last edited by Cracked Headtube; 04-28-2008 at 08:45 AM.

  6. #6
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    sweet.

  7. #7
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    Ordered mine up today....gonna be laced up to a stans ZTR 355 29" rim.

    Anyone interested in an ergomo pro??? for sale

  8. #8
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    Quote Originally Posted by sprocketjockey9
    Ordered mine up today....gonna be laced up to a stans ZTR 355 29" rim.
    Jason, where did you order from?

  9. #9
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    I ordered mine from my local shop: Geneva Bicycle Center, my guess is they called Saris and are able to get one? The shop is going to build it up to the hoop for me

  10. #10
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    funny, i too just order one and am lacing it to a stans 355 29er wheel....got mine from Rich at prowheelbuilder.com. they said a few weeks delivery....fingers crossed on that.

  11. #11
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    Saris has the hubs, just no rotors to go with them...I guess they've been selling extra rotors.

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    How much $dinero$ ?

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    i assume any standard rotor will work, yes?? i paid $1500 for mine.

  14. #14
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    Quote Originally Posted by William D
    i assume any standard rotor will work, yes?? i paid $1500 for mine.
    No, I believe they have a custom bolt pattern.

  15. #15
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    Quote Originally Posted by William D
    i assume any standard rotor will work, yes?? i paid $1500 for mine.
    Custom rotor. 8 bolt pattern.

    <a href="http://picasaweb.google.com/LyndaWallenfels/PowerMeterPics/photo#5192825346108037090"><img src="http://lh6.ggpht.com/LyndaWallenfels/SBCfI7dqF-I/AAAAAAAADYs/Cjk1ughLv3w/s400/DSC01746.jpg" /></a>

  16. #16
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    Just Received Mine!

    Thanks to American Classic and Red Rock Bicycle Co.
    IMG00107re.jpg
    Enjoy The Ride!

  17. #17
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    Quote Originally Posted by bn_acyclist
    Thanks to American Classic and Red Rock Bicycle Co.
    IMG00107re.jpg
    awwww she's luvly. We'll have to take them out for a ride together

    Was it plug and play for you or did you have to mess around with a few settings? How do you feel the power readings compare to your other PT's?

  18. #18
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    Plug and Play.

    Plug and play, I set the time and aranged the display how I like it before I rode. But it worked right out of the box.
    I only have one ride on her but the data I downloaded was perfect. It seemed to have way less if any holes in the data.
    Oh, BTW thanks for the consult. (LWcoaching) A few things that I learned in that informative meeting have led to the best year yet (so far, knock on wood). Thanks.
    Enjoy The Ride!

  19. #19
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    BN_A could you get me a Disc side photo of your wheel in the bike? A Similar angle to the one above, just from the other side.
    jeremy@amclassic.com

    thanks

  20. #20
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    Could someone please tell me what the actual weight of the hub with and without rotor is?

  21. #21
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    you can't get the hub w/o the rotor, as far as I know.

  22. #22
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    My PT Disk, with a 347g Stans 355 rim, 2.0/1.8 and 2.0/1.5 spokes 3x, Aluminum nips, Yellow tape, weighs 1030 without rotor. Add 160g for custom rotor, and also add for rotor bolts (x8).

    I did not get a chance to weigh the hub, but it looks like it should be very close to a standard PT SL (without rotor of course). You also need to add for the different axle, which I believe is steel.

  23. #23
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    Quote Originally Posted by perryr
    My PT Disk, with a 347g Stans 355 rim, 2.0/1.8 and 2.0/1.5 spokes 3x, Aluminum nips, Yellow tape, weighs 1030 without rotor. Add 160g for custom rotor, and also add for rotor bolts (x8).

    I did not get a chance to weigh the hub, but it looks like it should be very close to a standard PT SL (without rotor of course). You also need to add for the different axle, which I believe is steel.
    That seems dead on based on available info. Alum nips are ~10g per wheel, and the mix of spokes you have is ~165g per wheel. A few grams for the yellow tape, some subtraction, and I get 504g for hub only without rotor or rotor mounting hardware.

    Compared to Saris' web info quoting 680g less 160g for rotor as per Perry's post above, and maybe 15g for rotor bolts that gives 505g which is almost a dead match. Saris says the regular (i.e. road) PT 2.4 SL is 416g, so that means about 89g extra for all the extra material on the hub for the rotor mount, and any other changes they needed to maix it suitable for disc/MTB use.

  24. #24
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    Quote Originally Posted by Circlip
    Saris says the regular (i.e. road) PT 2.4 SL is 416g, so that means about 89g extra for all the extra material on the hub for the rotor mount, and any other changes they needed to maix it suitable for disc/MTB use.
    I bet most of that 89g is in the steel axle.

  25. #25
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    Built and ready to go for testing this afternoon






  26. #26
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    Just about ready

    My special savings account is about there! Did you build yours up yourself Jason? While I love to build, I rarely have the time. I'm considering, PT Disc / Olympics / DT 1.8-1.5 w/ alloy nipples. That way, if I want to race it, I can do so.

  27. #27
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    Nice. I ordered a wheel two weeks ago but the hub is backordered for a week due to the lack of rotors.

  28. #28
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    I wish I could build it up. If I did it probably would come out as a triangle or something....I can do everything 'cept that part.

    "stimulus check", just like my taxes.......deposited right at the bike shop

    I built mine up a little beefier with the ZTR and brass nipples as it will see some tough miles. I'll still race it, in fact racing it tonight. just not as light as the bonty x lites

  29. #29
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    mtb training w/power

    Jason, LMN, Lynda......whoever,
    How does training w/ power differ in the mtns. vs. the road, and what would you suggest doing when first getting started with it? My hub is here just waiting for my hoop to show up and then it's on. Also, any book recommends or site visits to help learn how to train better w/it?
    Thanks,
    Ryon
    If you do something often enough it tends to define you.

  30. #30
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    A great book is Racing and training with a Power meter by Allen and Coggan is a great place to start.

    Also http://www.cyclingpeakssoftware.com/power411/ is the lowdown on power training from the same people (the book expands upon these theories).

    the first thing I would do with it is to determine your power training zones, on the power411 page is a brief description on how to set up your zones.

    The big difference between road and off road power, in my belief comes down to quandrant analysis. While power is power across the board, how you produce it is a little bit different off-road. Unfortunately, a review of this is only available after a workout and not during. Road tends to be high force/high rpm, while mountain biking is high force/low rpm.

    With the power meter you can also get "data" proof of your actual weaknesses and target it exactly. Kinda like using a laser sight to hone in on your target, vs blind firing.

  31. #31
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    So, last year I tested with my road power tap and got some numbers for a 20 min. test and they were pretty accurate for a twenty min. based on the 4 hill climbs I did. They were plus or minus 10 watts. Are these numbers a good place to start? also, is average power a good indicator of your ride or go by tss. I have limited knowledge here so I am throwing out vocab. stuff w/limted info. sorry
    Thanks,
    Ryon
    If you do something often enough it tends to define you.

  32. #32
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    Quote Originally Posted by butryon
    So, last year I tested with my road power tap and got some numbers for a 20 min. test and they were pretty accurate for a twenty min. based on the 4 hill climbs I did. They were plus or minus 10 watts. Are these numbers a good place to start? also, is average power a good indicator of your ride or go by tss. I have limited knowledge here so I am throwing out vocab. stuff w/limted info. sorry
    Thanks,
    Ryon
    You can use those numbers as a start, but I'd still recommend trying to get a real test in. Understandably, it's probably pretty hard to do off-road 20 minute test or so, but just give it your best effort on a section of trail or a road where you can recreate it. I think TSS gives more value to a workout than an avg power number. If you're using wko+ you can use the Performance Chart Manager and track TSS and see how it influences your form and fitness.

    If you're really interested in the fine detail of power there is a google group on "wattage".

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    Thanks Jason,
    As I get going more I will drive you crazy w/ some ?'s following a true dirt 20 min. Should I shoot for a 30 min.?
    Thanks again,Ryon
    If you do something often enough it tends to define you.

  34. #34
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    Quote Originally Posted by butryon
    So, last year I tested with my road power tap and got some numbers for a 20 min. test and they were pretty accurate for a twenty min. based on the 4 hill climbs I did. They were plus or minus 10 watts. Are these numbers a good place to start? also, is average power a good indicator of your ride or go by tss. I have limited knowledge here so I am throwing out vocab. stuff w/limted info. sorry
    Thanks,
    Ryon
    I always have my athletes test on the pavement even if they are on their mtb - fewer variables to interrupt the test.

    Do a new test to be sure you are setting your power training levels on up-to-date info.

    The more technical a course is the lower your mtb FT will be. As you ride on all different types of courses the exact FT to use to calculate TSS for an mtb ride on a daily basis is a bit of guesswork. In general I use an FT 5% lower for mtb rides than the road FT for TSS purposes.

    Tracking daily TSS in the Performance Manager Chart is the bomb for training planning and nailing peaks.

  35. #35
    zrm
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    I don't need to spend that kind of moola to get confirmation of what I already know.

    I'm weak.

  36. #36
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    Quote Originally Posted by butryon
    Thanks Jason,
    As I get going more I will drive you crazy w/ some ?'s following a true dirt 20 min. Should I shoot for a 30 min.?
    Thanks again,Ryon
    No problem, Once you do your 20 min test (in agreement with Lynda as far as testing on the road vs. dirt) there's no real need to move onto a 30 minute test. 20 minute is the norm and you can just extrapolate your FTP from there. 20 min ~ 95% or so of your FTP

  37. #37
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    Lynda and Jason,
    So, based on my 20 min. test and three Hillclimbs last year I came up w/ a 20 min. of 333 watts, averageing the 4 rides. that will put my ftp at 316(333*.95) correct? and then expect 5% less than that on dirt = 300.2 watts.
    Based on these numbers where will most of my training for mtb racing be at? I generally only ride the road a few times a month, hence, why I sold my road power tap.
    Thanks again,
    Ryon
    If you do something often enough it tends to define you.

  38. #38
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    Ryon,
    Well it really determines how your power curve lies. That will help determine your weakness. Secondly, it depends on your goals. Are you racing xc, short track or endurance??

    The numbers you have given sound like a good place to start with your FTP

  39. #39
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    Jason,
    I am racing mostly xc for the first half of the season and then ramping the volume up a bunch for the Trans Rockies in Aug. so the end of June and all of July are longer races. I notice that the longer 2.5 to 3.5 hr races I have my best performances. Not sure what that means but power should help me add a bit more structure to what i do.
    Thanks,
    Ryon
    If you do something often enough it tends to define you.

  40. #40
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    Quote Originally Posted by butryon
    Jason,
    I am racing mostly xc for the first half of the season and then ramping the volume up a bunch for the Trans Rockies in Aug. so the end of June and all of July are longer races. I notice that the longer 2.5 to 3.5 hr races I have my best performances. Not sure what that means but power should help me add a bit more structure to what i do.
    Thanks,
    Ryon
    Well cool. I'll see you at TR. I'm signed up to race open mixed again.

    For TR lots of long tempo rides in power L3 is the ticket. Build up gradually to 120 mins non-stop on the gas in power L3. Do that a couple of times a week 3-5 weeks out from the start of TR.

    LW

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    Lynda,
    what is L3 compareable to in terms of hr(max 186), and what wattage based on a 330w, 20 min. test?
    Also, I know some of you have had a power tap on the mtb for a while, what do I need to be careful with? What shouldn't I do and how durable are they?
    Thanks,
    Ryon
    If you do something often enough it tends to define you.

  42. #42
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    Ok... I'll bite.
    Why the different rotor bolt pattern?

    Seems like an annoyance more than anything.
    www.mtbiker.ca

    My Rides:
    FSR XC -R7 Platinum - SRAM X7 (26.5lbs)
    Cervelo SLC - SRAM Rival - Reynolds DV46T (16.25 lbs)

  43. #43
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    Quote Originally Posted by bbgobie
    Ok... I'll bite.
    Why the different rotor bolt pattern?
    Check out lynda's picture



    The hub is much bigger. Requires a custom rotor.

  44. #44
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    Quote Originally Posted by LyndaW
    Well cool. I'll see you at TR. I'm signed up to race open mixed again.

    For TR lots of long tempo rides in power L3 is the ticket. Build up gradually to 120 mins non-stop on the gas in power L3. Do that a couple of times a week 3-5 weeks out from the start of TR.

    LW
    Are you and Dave taking a laptop there to download between stages? I want one too but I'd end up erasing each file without knowing my CP's and TSS.
    If you believe that I've got some magic beans to sell ya.

  45. #45
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    Quote Originally Posted by butryon
    Lynda,
    what is L3 compareable to in terms of hr(max 186), and what wattage based on a 330w, 20 min. test?
    Also, I know some of you have had a power tap on the mtb for a while, what do I need to be careful with? What shouldn't I do and how durable are they?
    Thanks,
    Ryon
    Your L3 power would be 235 - 280 watts. The heart rate for this power level depends, among things on how long you have been there, how hot it is, how fresh/fatigued you are, how much coffee you have drank, how many stages into a 7 day stage race you are...

    The wireless PT's - you have to be careful on keeping communication between the hub and CPU.

    Cheers,

    Lynda

  46. #46
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    Quote Originally Posted by jakomonster
    Are you and Dave taking a laptop there to download between stages? I want one too but I'd end up erasing each file without knowing my CP's and TSS.
    Oh I'd love to but we are coming with no support and sleeping in a tent so don't feel like putting a laptop in the gear bag thrown in a truck daily. Do you guys have a support team? If someone can take care of a laptop between stages it would be doable. We can all share and snicker over power files at dinner time...

  47. #47
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    Those of you that have gotten a few rides on your new hubs:

    Any issues? Does the signal drop out much? Would you do it again?

    Thanks,
    OnTheFence!

  48. #48
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    Quote Originally Posted by JMK331
    Those of you that have gotten a few rides on your new hubs:

    Any issues? Does the signal drop out much? Would you do it again?

    Thanks,
    OnTheFence!
    I've put some time so far in on mine, including a nice 8 hour ride this past saturday. I've haven't had any power or data drops. If I'm off the bike for a few minutes, I might sometimes have to do a find to bring the power back, however with hr anytime I move out of range I'm forced to do a find. Kind of annoying and scary at the same time (find is really close to clear all).

    After breaking in the rotor in it's worked great including on some super long forearm burning, brake fade heat inducing descents.

    I ran an ergomo pro all of last season and still have it set-up, but I've yet to run the power-tap on the same bike and do a side by side comparison. So far the numbers seem pretty accurate

  49. #49
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    Quote Originally Posted by JMK331
    Those of you that have gotten a few rides on your new hubs:

    Any issues? Does the signal drop out much? Would you do it again?

    Thanks,
    OnTheFence!
    I've got a few hundred miles on mine, which I built into a heavier training rim. Honestly, I'm super tough on gear. It's been ridden through rain, mud, slop, high humidity, creeks, and most recently submerged completely into a hub deep mud pit. It's worked flawlessly. I agree that the "find" is a little too close to the "clear" function for my comfort, but otherwise it's an awesome tool.

    Truthfully, I'm new to the whole "power training" phenomenon. Being a total gear junkie, I bought it mostly because it's new, cool, and shiny. However, I raced my first xc race of the season on it and got some really good info. I have no idea what most of it means, but "coach" says it was valuable. I'd totally spend the cash again.
    required disclaimer: I'm a bike shop girl.

  50. #50
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    Quote Originally Posted by JMK331
    Those of you that have gotten a few rides on your new hubs:

    Any issues? Does the signal drop out much? Would you do it again?

    Thanks,
    OnTheFence!
    I have been using a PT wireless rim brake wheel on my MTB for about 8months. Did numerous races, mud, rain, sub freezing, about 5000 miles.

    Down around 10deg the display fades, but continues to record.. just stay on top of your batteries in the cold. I rode in heavy rain, freezing rain, snow, etc.. no issues.

    After a mud race I had to submerge my bike to get the mud off before
    putting it in my car. The next day it was dropping out, so I opened up the battery compartment and dumped the water out, let it dry and its been fine ever since. Definitely a solid unit!

    The Disk version is basically the same with the shell modified to accomidate the disk. Killer hub!

  51. #51
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    Thanks for all the great input. I ordered one today!

  52. #52
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    Hi, I wonder if anyone can help me. I'm trying to build a wheel on this hub (Powertap SL MTB Disc) and my rim is a mavic 717 non-disc rim (so i can use it in both types of brake system) I used an online calculator and it's giving me 259.++ at one side and 258.++ at the other side is it safe to use a 258 spoke length at with both sides then? This is at 3x lacing. Thank you.

  53. #53
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    Quote Originally Posted by mgarrucho
    Hi, I wonder if anyone can help me. I'm trying to build a wheel on this hub (Powertap SL MTB Disc) and my rim is a mavic 717 non-disc rim (so i can use it in both types of brake system) I used an online calculator and it's giving me 259.++ at one side and 258.++ at the other side is it safe to use a 258 spoke length at with both sides then? This is at 3x lacing. Thank you.
    The Wheels & Tires forum is a better place for this type of question, but I'd go with 260mm for the long side. Depending on where your 259.xx is within the decimal range, you could easily come up 1.5mm short (or more) which is going to place extra stress on the nipple and threads that are in contact, if you go with the shorter 258mm. Not an issue in most cases if the spoke is a fraction too long, assuming it's not so much longer that you bottom out against the last of the threads before reaching your target tension.

  54. #54
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    Is anyone using their Powertap with the Joule 2.0 computer? The exposed USB port on the back of the computer has me a little concerned about how it's going to hold up in wet weather.

    The Joule 2.0 computer appears to be potentially quite good but definitely has some quirks - Mine doesn't always connect properly to a Windows 7 64 bit PC with it either not being detected or the CycleOps Power Agent software (7.5.1.19) crashing when you're trying to update settings on the device.

    One big issue is that although the Joule 2.0 has a barometric altimeter built in there doesn't appear to be a way to manually calibrate the starting altitude. If you can't manually calibrate the altitude then it means the altitude data will always be wrong. It's currently showing -127 ft below sea level when it should be 45 ft above sea level. Hopefully a firmware update will fix that sometime.

    I do like the way that you can customise the number of lines on the display. You can choose from 6, 4 or 3 lines of information where 3 lines has one really big number in the middle of the screen that should be easy to see when riding.

    My Powertap SL+ hub is still off being built up so I haven't had a chance to actually try it out properly yet.

  55. #55
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    Quote Originally Posted by WR304
    Is anyone using their Powertap with the Joule 2.0 computer? The exposed USB port on the back of the computer has me a little concerned about how it's going to hold up in wet weather.

    The Joule 2.0 computer appears to be potentially quite good but definitely has some quirks - Mine doesn't always connect properly to a Windows 7 64 bit PC with it either not being detected or the CycleOps Power Agent software (7.5.1.19) crashing when you're trying to update settings on the device.

    One big issue is that although the Joule 2.0 has a barometric altimeter built in there doesn't appear to be a way to manually calibrate the starting altitude. If you can't manually calibrate the altitude then it means the altitude data will always be wrong. It's currently showing -127 ft below sea level when it should be 45 ft above sea level. Hopefully a firmware update will fix that sometime.

    I do like the way that you can customise the number of lines on the display. You can choose from 6, 4 or 3 lines of information where 3 lines has one really big number in the middle of the screen that should be easy to see when riding.

    My Powertap SL+ hub is still off being built up so I haven't had a chance to actually try it out properly yet.
    I'm going to pair mine with a GPS unit so I don't go off trail anymore! haha

  56. #56
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    One good thing about having an ANT+ powermeter is that you can always just change the head unit for another model easily.

    A Garmin Edge 705 or Garmin Edge 500 is cheaper and has more features but articles like these ones about lost and corrupt data are a bit worrying. That was my main reason for trying a Joule 2.0 computer instead of a Garmin.

    https://forums.garmin.com/showthread.php?t=10297

    http://blog.kyanmedia.com/archives/2...data_recovery/

    http://www.dcrainmaker.com/2009/11/g...th-review.html

    Some interesting discussions of Powertap calibration and accuracy:

    http://weightweenies.starbike.com/fo...hp?f=8&t=69621

    http://biketechreview.com/forum/1-ge...ation-part-two

    I'm still trying to get the WKO+ 3.0 software setup as I'd like also. WKO+ 3.0 has a few good features but there are some really poor bits also. Multi File/ Range Analysis is a good example of a feature that needs sorting out so that you can actually compare rides properly. Having an X axis that can be switched between Time and Distance so the overlays line up would be a good start...

  57. #57
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    I got the built up Powertap wheel back today. I took the black plastic cover off and put some marine grease over the seals to try and help with weather proofing. There are two o-ring seals and only a small amount of visible electronics inside. You have to be careful with the plastic threads of the cover as they seem easy to cross thread. In order to remove the cover you have to take the brake rotor off first.

    The Joule 2.0 computer is still playing up though. I fitted a 2gb MicroSD card but in Windows 7 64 bit it's only being detected occasionally. The picture below shows what happens when you connect the Joule 2.0 via USB to a PC running Windows 7 64 bit. Drive H: (Joule 2.0 onboard memory) and Drive I: (Joule 2.0 MicroSD card) both appear as the same size and the data on the MicroSD card isn't accessible. If you unplug and replug it a few times you can occasionally get the MicroSD card to appear but most of the time it just ends up like below.

    The Joule 2.0 USB connectivity appears to work ok with Windows XP however so if there isn't a way to fix it in Windows 7 I might have to copy the .bin recorded data files onto another PC and then copy them across to WKO+ 3.0 that way..

    It's not just my unit having these issues:

    http://forum.slowtwitch.com/Slowtwit...RS..._P2770431

    At least with a Powertap hub I should hopefully avoid the incorrect speed issues that the Joule 2.0 appears to have when used with a seperate ANT+ speed sensor:

    http://forum.slowtwitch.com/Slowtwit...r_Not_P2998780

    Pictured below: Powertap SL+ MTB disc hub internal pictures showing seals and batteries.

    CycleOps Joule 2.0 connected via USB to a PC running Windows 7 64 bit has problems detecting the internal 2gb MicroSD card.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-powertapinternals.jpg  

    PowerTap Disc-powertapseals.jpg  

    PowerTap Disc-joulememorywindows7.jpg  

    Last edited by WR304; 10-29-2010 at 03:26 PM.

  58. #58
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    I've done a few rides with the Powertap and Joule 2.0 computer now.

    I took the Epic out on the road club run today and one side effect of the new Powertap was that my mates were doing some serious half wheeling whenever I was on the front - just for a laugh so they could look over at the display and see what power I was having to produce to keep up.

    The power data is really interesting to look at. The difference between what the heart rate / speed readings on the display show and what the power numbers read at the same time is really striking. The main thing is that power output seems very sensitive. Even when speed and heart rate appear constant (such as when climbing a hill) the power can fluctuate a lot. I couldn't believe how much I appeared to be backing off at some points on one climb where there was clearly room for improvement as I could have changed up a gear or two. That's not something I'd noticed from just looking at heart rate / speed in the past.

    Another aspect that I hadn't appreciated was just how clear the power data is for showing if you're tiring towards the end of the ride. I was starting to feel it towards the end of the ride today and even though my heart rate stayed constant the power readings dropped off a cliff for the last 40 minutes of the ride as I couldn't sustain the tempo. What you can then do is to look back through the preceding hours to see how much energy you used and how many big efforts you put in to understand why it happened.

    My actual power numbers are about what I expected them to be.

    Joule 2.0 whilst riding
    On the bike I've got smoothing of 5 seconds for the power display including zeroes so that the wattage numbers are a bit more stable and don't jump around too badly. If you have 1 second data displayed the watts are all over the place. eg: the power display with one second data whilst riding at a steady constant pace would read in succession over 5 seconds - 163w, 241w, 249w, 153w, 266w. A figure that updates less frequently is much easier to gauge and use for pacing when riding.

    Whilst riding the actual screen isn't too difficult to read. With the full six lines of data the top two lines are easiest to glance at quickly whilst the lower ones take a little more effort. Having the computer mounted on the stem isn't that great however because the screen is vulnerable to getting covered in sweat. Add some dirt in and it ends up smeared. The two yellow buttons (mode and interval) are usable whilst riding but the joystick and small text of the menus is quite fiddly to navigate when wearing full finger gloves.

    The claimed battery life of 20 hours looks like it's exaggerated. With power and heart rate sensors connected but no backlight the battery has been down to two blobs remaining after 4 hours riding. 8-10 hours is probably a more realistic battery life.

    Joule 2.0 connected to a PC via USB
    The Joule 2.0 with firmware 14.063 really doesn't work well with Windows 7 64 bit. It's fine in Windows XP but a nightmare with Windows 7 64 bit as it can't see the MicroSD card. I've taken the MicroSD card out now and intend to use it with the 4mb of internal memory instead. This can usually be viewed in Windows 7 64 bit. A typical ride file size with power and heart rate appears to be around 100kb per hour of ride time so the 2gb MicroSD card isn't essential so long as you remember to delete the activity files occasionally.

    The included CycleOps Poweragent 7.5.1.19 software is just rubbish. I've been changing settings on the Joule 2.0 through the onscreen menus instead because at least that works. You can copy the .bin activity files off the unit without needing the Poweragent software.

    Joule 2.0 with WKO+ 3.0 build 47
    WKO+ 3.0 can import the .bin recorded files from the Joule 2.0 directly which is what I've been doing. The data appears to be ok and the intervals recorded by pressing the "interval" button whilst riding appear. One quirk is that it doesn't place an interval at the start and end of the data. If you want to look at an interval from the start of the ride until the first time that you pressed the "interval" button then you need to manually add one in WKO+. The same thing occurs between the last time that you press the "interval" button and the end of the ride which also needs an interval manually adding.

    It's worth spending some time going through a recorded file and annotating the intervals with enough details that you can come back to the file and work out where you were at a particular point. This makes it easier to look at an old file in the future. For example I'll always have an interval split time for the main hills, along with intervals for the major sections of a ride.

    When looking at the power data in WKO+ it's worth applying some smoothing so that you can see the trends more clearly. Smoothing of 5 seconds seems to be about right so that you have a clear line for power instead of a constantly changing trace that's hard to follow. Hiding the traces that you don't use all the time helps to make the graph clearer also. I'll usually turn off cadence.


    Pictured below: Sample section of recorded Powertap data in WKO+ 3.0. This interval shows a climb on the way out of town. The starting altitude is completely wrong but gradient % and meters ascended seem about right. If you look at the power trace you can see how it jumps around a lot whilst my speed and heart rate remain constant.

    The big jump in power near the top is where I lifted the pace to chase down and catch a road bike who'd just turned out of a junction near the top. You can see the sharp spike of acceleration which drops off once I'm on his wheel recovering before going past shortly after the top of the climb.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-powertap_hill_power.jpg  


  59. #59
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    Is that the same hub you asked Mike to build into my wheel? Brian says the wheels arrived in his shop on Friday and look awesome!
    redheeler

  60. #60
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    Quote Originally Posted by redheeler
    Is that the same hub you asked Mike to build into my wheel? Brian says the wheels arrived in his shop on Friday and look awesome!
    My wheel is a Powertap SL+ MTB disc hub (manufacture date on the packaging was June 2010) with a black DT Swiss XR 4.2D rim, DT competition spokes and brass nipples. It certainly looks distinctive fitted on the bike with the massive hub and bulky brake rotor.

    The hub bearings seem to spin freely, the freehub isn't too clacky and the brake rotor works fine with my Hope Tech X2 brakes. So long as the weather seals hold up it's just like any other hub in use.

    Weight for my rear wheel including the 160mm custom brake rotor (weighs 160g approx) & rim tape but without a cassette or skewer came to 1250g approx. That's a weight increase of 350g or so if you're currently using a lightweight wheel and lightweight brake rotor but since I split the rim on my old wheel a while ago I've just been riding around on a generic wheel off an old bike that I had lying around (DT freehub, 32 spokes, DT Swiss 420SL rim). Compared to that wheel with a Hope 160mm floating rotor the Powertap wheel has only added 75g to the bike. The Joule 2.0 computer is about the same weight as my Polar RS800CX with speed and cadence sensors so the change hasn't really added as much weight to the bike as I'd expected.

    Even if you don't want to look at the data in depth power data can give you a useful overview of how a ride went. The graph below is for the road club ride I did yesterday but smoothed to 10 minutes in WKO+ 3.0 . This loses a lot of the detail but allows you to look at overall trends. I've highlighted the three sections of the ride in green so that you can see how the power output changes. The three dotted yellow lines are the edge of my (estimated) power zones. Anything above the lower dotted yellow line but below the middle dotted yellow line is Tempo (per Coggan zones). Anything above the middle dotted yellow line but below the upper dotted yellow line is trying hard Threshold (per Coggan zones) Anything above the upper dotted yellow line is above threshold and trying very hard VO2MAX or Anaerobic Capacity (per Coggan zones). With this level of smoothing on the graph you lose the highest peaks and troughs of the power output but what remains is an indication of overall effort that you were putting in.

    (Edit: Corrected description of power zones)

    The first section is riding to meet the club plus the first few miles of the ride where I was sitting in the group chatting. If you're not on the front then it takes a lot less effort to ride at the same pace due to slipstreaming the riders in front. You can see this in how far below the yellow dotted lines the smoothed power output falls.

    The second section is riding with the club but now I'm spending some time on the front for the lead in to the climb which was flat out (the highest power output / lowest speed peak) followed by working harder afterwards for the next 18 miles or so with some long stints on the front of the group into the wind.

    The third section is the interesting part. I'm now riding by myself on the way home. Although my speed still isn't too bad I'm tiring now and can't sustain the same power output anymore. This shows up very dramatically as the yellow power output trace falls away towards the end. It's really only the last 1.5 miles which is truly a descent back into town. The rest of this section superficially appears solid enough if you were just looking at the speed trace and heart rate but by looking at the power output in this way it shows that I was cracking.

    At that point in the ride I was struggling. By looking at the overview of the entire ride you can see why. Throughout the club ride section I'm going into the red repeatedly and paid for it later on. You can use the smoothed view to pick out overall trends and then see if you repeat them across more rides. If you're always losing power after 2h30 for example then it's a sign that maybe you need to pace yourself more carefully early ride or possibly eat and drink more.

    Pictured below: Changing power output during Sunday's club ride.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-powertap_club_run_sections.jpg  

    Last edited by WR304; 11-04-2010 at 03:59 PM.

  61. #61
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    Using the Joule 2.0 computer without a MicroSD card has been working fairly successfully. I've been able to get the .bin recorded ride files off without any problems and copy them onto the Windows 7 64 bit PC.

    After the first rides where the computer battery went down quickly the battery life seems to have improved now after a few charges. It was still displaying full battery after 3h30 on the bike today which seems much better also.

    I've been trying to compare the Powertap recorded data to what was produced by my Polar RS800CX which recorded heart rate, speed, cadence and altitude. There are a few interesting differences that I've been trying to understand why they're happening. The main one is that the distance recorded by the Joule 2.0 (with Powertap hub) is reading higher than the Polar by about 1.4% when both were using the same tyre and identical circumference measurement.

    Another big difference is in the cadence readings. The virtual cadence of the Powertap hub is all over the place. I'm thinking about getting a VDO Z-Series ANT+ cadence sensor so that the cadence readings are more accurate than the virtual ones. I don't use cadence for much but I do like to look at the amount of time that I spent not pedalling over an entire ride. As an example over a 3hr ride with the Polar RS800CX recorded data it said that I had free wheeled for 6min39 seconds according to WKO+. When I did the same ride yesterday with the Powertap the recorded data said that I had freewheeled for 14min14 seconds over the same route.

    I've also been experimenting with some different values for power smoothing whilst riding. I ended up going back to 5 second smoothing as that seems best. If you increase smoothing to 10 seconds then the display still updates with a new figure every few seconds. Smoothing doesn't mean that the power figure displayed stays constant on the screen for 5 or 10 seconds. It just seems to mean that the power figure lags more behind your current effort.

  62. #62
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    Well the Joule 2.0 and Powertap survived their first wet ride today. It was ok for 3 hours but then the rain came in for the last hour of the ride on top of the hills. It was just drizzle but everything is still working.

    There are some more odd things that I've been noticing. According to the History report viewed directly on the Joule 2.0 today's ride involved 5267 ft of elevation gain. The recorded ride file viewed in WKO+ for today's ride says that it only involved 4404 ft of elevation gain. Today's ride was all above sea level but if you do a ride where the altitude is below sea level then WKO+ interprets any altitude readings from Joule 2.0 below sea level as a fixed -3ft. Any altitude data below sea level is ignored.

    Another one is the TSS and IF calculated by the Joule 2.0. I have exactly the same FTP and power zones entered into the Joule 2.0 and WKO+. According to the Joule 2.0 History report today's ride had a TSS (Training Stress Score) of 285.6 and an IF (Intensity Factor) of 0.827. The recorded ride file viewed in WKO+ for today's ride says that it had a TSS of 287.9 and an IF of 0.832. It's not a massive difference but there shouldn't be one at all.

    Normalised power, average power, KiloJoules, time, distance and average speed were the same between both the Joule 2.0 and WKO+.

    In order to enter your FTP into the Joule 2.0 you have to do it through the CycleOps Poweragent software. You can set the power zones on the head unit but FTP can only be entered via a computer and the USB connection. The Poweragent software works perfectly on Windows XP (apparently it's ok with 32 bit Windows Vista and 32 bit Windows 7 also. The problem being the 64 bit operating system compatibility.)

    Being able to track TSS and IF in WKO+ is something that looks like it will be really useful as it allows you to quickly have an idea of just how hard a particular ride was. One problem I had when using a heart rate monitor for training was that my heart rate response would drop off rapidly after a few days consecutive riding to the point where the heart rate numbers didn't mean much. I'd be riding around at some ridiculously low heart rate that was way below any training zones but with good pace and no real idea of how hard a ride was in comparison to other rides.

    Pictured below: Any Joule 2.0 altitude data below sea level doesn't appear in WKO+ 3.0
    Attached Thumbnails Attached Thumbnails PowerTap Disc-joule_wko_altitude_below_sea_level.jpg  

    Last edited by WR304; 11-03-2010 at 05:00 PM.

  63. #63
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    Quote Originally Posted by WR304
    today's ride says that it had a TSS of 287.9 and an IF of 0.832. .
    BIG ride! 4h15min?

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    Quote Originally Posted by perryr
    BIG ride! 4h15min?
    It was 4h11min. I would have done another hour or so but had to cut it short because the bite valve on my hydrabak bladder started leaking badly and I was worried about running out of drink.

    The weather's been quite nice recently so I've been trying to get some miles in. 18 hours in the last 5 days.

    TSS and IF are really reliant on your FTP figure being accurate. From looking at the WKO+ power distribution chart and the gaps between bars I think that I'm in the right sort of area but I haven't actually done a proper test yet. I could be underestimating my FTP which would make the current TSS and IF numbers a bit too high.

  65. #65
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    Quote Originally Posted by WR304
    Another one is the TSS and IF calculated by the Joule 2.0. I have exactly the same FTP and power zones entered into the Joule 2.0 and WKO+. According to the Joule 2.0 History report today's ride had a TSS (Training Stress Score) of 285.6 and an IF (Intensity Factor) of 0.827. The recorded ride file viewed in WKO+ for today's ride says that it had a TSS of 287.9 and an IF of 0.832. It's not a massive difference but there shouldn't be one at all.
    Check the wattage forum, but I'm not sure they use the same calculation. While close, it may not be exact.

  66. #66
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    Quote Originally Posted by WR304
    It was 4h11min. I would have done another hour or so but had to cut it short because the bite valve on my hydrabak bladder started leaking badly and I was worried about running out of drink.

    The weather's been quite nice recently so I've been trying to get some miles in. 18 hours in the last 5 days.

    TSS and IF are really reliant on your FTP figure being accurate. From looking at the WKO+ power distribution chart and the gaps between bars I think that I'm in the right sort of area but I haven't actually done a proper test yet. I could be underestimating my FTP which would make the current TSS and IF numbers a bit too high.
    For myself, 287 TSS on an MTB, off road, with 5k climbing, in 4hr 11min.. would be the kinda ride that would put me on the couch.. right after I emptied the refridgerator. The ride would have had plenty of time riding hard, and the last hour would have been somewhat brutal.

    The same ride at a somewhat casual pace, still hard.. but with enough in the tank to do another hour, would be 230ish.

    If your 287tss ride felt like more of an endurance pace (but still a lot of work), then you may be understating your FTP by 10-15%.

    If you can't find a good spot for a 20min test, go do 4 or 5x10min repeats up a hill at a power you can hold fairly consistent from 1st to last.. that'd be quite close to FTP. Better to do them in a somewhat "un-fresh" state. For instance, do your big ride, rest a day, then the next day do the 5x10's. You'll have enough to do some 10min threshold efforts, but not that extra bit needed to repeat at levels above threshold.

  67. #67
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    Quote Originally Posted by perryr
    The same ride at a somewhat casual pace, still hard.. but with enough in the tank to do another hour, would be 230ish.

    If your 287tss ride felt like more of an endurance pace (but still a lot of work), then you may be understating your FTP by 10-15%.
    Yesterday's ride was on the mountain bike (as that's my only bike) but on tarmac with slicks on. It was a fairly hard ride but not ridiculous. The 4404ft of elevation gain from WKO+ is more likely to be accurate than the 5257ft of elevation gain from the Joule 2.0.

    Those TSS and IF figures were really just to compare between the Joule 2.0 and WKO+ figures. It's a bit frustrating that the Joule 2.0 can't seem to get the basic calculations right. I've been trying lots of different FTP figures in WKO+ but it doesn't seem possible to make the TSS and IF between the Joule 2.0 and WKO+ match exactly. Maybe they'll fix it with a firmware update sometime.

    I was feeling ok today and it wasn't too wet so I included a 30 minute interval down the A38 in the ride to try and get a feel for what my actual 1 hour time trial FTP figure might be. I was feeling quite good and it made a nice change doing a short 2 hour ride. I've attached a picture of the 30 minute interval graph below because it shows a few interesting things, especially when you compare the yellow power trace to the red heart rate trace.

    If you look at the altitude trace along the bottom of the graph then you can clearly see the problem that the Joule 2.0 data in WKO+ has when altitude is below sea level. Anything below sea level just ends up as a flat line. I find altitude is a useful trace to look at as it can help you understand why there are changes in other traces. In this case having the changing altitude visible would help explain why the speed and power are going up and down so much over the course of what ought to be a flat time trial.

    The A38 down to Bristol is quite flat with only some drags and small power climbs and is normally quite fast. It was blowing a gale today though. The entire 30 minutes was into a crazy headwind. I was going flat out and at one point was down to 10mph and the 33T middle ring. That's why the average speed is so low.

    When you compare the average power output to the average heart rate it shows why I've found it difficult to use recorded heart rate as a reliable measure of intensity. Heart rate relative to how hard I'm trying doesn't stay constant from ride to ride. The highest heart rate figure that I've seen this year when totally fresh was 197bpm. The average heart rate for this 30 minute time trial today where I was flat out was only 155bpm. A full 42 beats below that. If you look at those heart rates compared to the Peter Keen heart rate zones for example then 155bpm would indicate that this was a low level aerobic workout, barely above active recovery when I was actually trying to go as fast as possible.

    http://www.machinehead-software.co.uk/keencalc.html

    Even with the head wind you can see how the power trace falls away anytime the speed rises. It's a struggle to keep the power high at those points on the downhills making my pacing appear a bit inconsistent. This is something that a power meter shows up really well. It takes a lot of concentration to stop your work rate falling away on downhill sections. Doing a test like this on the turbo trainer or up a climb would probably give a much smoother power output overall than I managed here.

    I had a look back through the other power data and there was a section of the club ride on Sunday where I managed 250 watts for 17 minutes whilst I was leading out to the bottom of the hill and then trying to stay with other riders uphill which is a substantially higher figure than the time trial today. An FTP number in that sort of range would make the TSS for yesterday's hilly ride more like what perryr expected to see. I'm going to do another test next week, probably uphill, and see what the power figures are like from that when I'm more rested.

    Although I felt quite good today I suspect that I was actually a bit tired and could have managed a higher average power if I'd had a few days off first or chosen a different route. This is the good thing for me about having a power meter as it's a measurement that shows when I could benefit from some time off with less guess work than looking at heart rate.

    Pictured below: 30 minute time trial on A38 into a head wind
    Attached Thumbnails Attached Thumbnails PowerTap Disc-30_min_timetrial.jpg  

    Last edited by WR304; 11-04-2010 at 03:39 PM.

  68. #68
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    Quote Originally Posted by WR304
    I had a look back through the other power data and there was a section of the club ride on Sunday where I managed 250 watts for 17 minutes
    250*.95=238

    That may be close?

    There are all sorts of do's and don'ts when calculating FTP. Its good to have it reasonably close as the training zones are more accurate, and that is important to me.

    I also track TSS with Performance manager, and use PM to help steer my training. Its also amazing for looking back on what worked, what didn't and what we might try different to find improvement. For this reason I think the testing protocal is critical to accuracy down the road when comparing seasons etc..

    I use a standard 20min x.95. Its long enough to come close, but not so long and difficult that testing requires a special day, with a wekk taper and huge motivation (like a 40k).

    I also use the same road.. a very mild climb that I'm very familiar with. I ride it all the time, I know how to pace it and its 10min from my house. I'll adjust FTP periodically to reset training zones and know for sure that TSS is relatively accurate. When I look back at 08', I know the FTP was set in the same way as today, and that the PMC compared with today is apples to apples.

    So, my recomendation would be to seek out a test prtocal. Find the course, make sure you have a few days of recovery, do some openers the day before and then put the hammer down for an all out best avg watts. Down the road you'll be happier with the accuracy of the ride histories and the PMC.

  69. #69
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    Quote Originally Posted by perryr
    I also use the same road.. a very mild climb that I'm very familiar with. I ride it all the time, I know how to pace it and its 10min from my house. I'll adjust FTP periodically to reset training zones and know for sure that TSS is relatively accurate. When I look back at 08', I know the FTP was set in the same way as today, and that the PMC compared with today is apples to apples.
    I'm glad that you mentioned those TSS figures seemed high.

    Doing that 30 minute time trial yesterday showed how important it is to sort out a good route and test properly. If the FTP and TSS are incorrect then it makes it difficult to know if all the other reports derived from those figures are reliable or not.

    I've got several years of historic recorded heart rate data in the Polar Protrainer 5 software. I imported October's Polar files into WKO+ but it's quite a lot of hassle because the ride details and split time text notes aren't imported with the Polar .hrm files and have to be copied in afterwards. Without power data most of the WKO+ reports don't work anyway so I'm thinking about just leaving the rest of the files in the Polar software.

    The picture below shows my Powertap wheel fitted to the bike. The area around the rear axle manages to look even more cluttered than before with the bulky hub.

    The Joule 2.0 headunit isn't that big. Here it's mounted on a 110mm Extralite stem. The first thing anyone who sees it asks is whether it's a GPS. It's larger than a standard computer but smaller than a Garmin Edge 705. Something interesting is that the grey and yellow colour scheme of the Joule 2.0 is exactly the same as the cover of the "Training and racing with a Power Meter" book. I think it might be deliberate.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-powertap2b-.jpg  

    PowerTap Disc-powertap_joule.jpg  

    Last edited by WR304; 11-05-2010 at 05:19 PM.

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    Quote Originally Posted by perryr
    250*.95=238
    I looked at my WKO+ charts and checked what the "Mean Maximal Power" curve shows for the difference between 17min and 20min. For me, the difference in the best power I can do for 17min and that of 20min is a 1-watt difference.

    Therefor using 95% of 250 is reasonable. I'd bet that in future tests you will be very close (if that 17min was a max effort in a rested/recovered condition).

  71. #71
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    Quote Originally Posted by perryr
    I looked at my WKO+ charts and checked what the "Mean Maximal Power" curve shows for the difference between 17min and 20min. For me, the difference in the best power I can do for 17min and that of 20min is a 1-watt difference.

    Therefor using 95% of 250 is reasonable. I'd bet that in future tests you will be very close (if that 17min was a max effort in a rested/recovered condition).
    That 17 minute effort last Sunday on the club ride wasn't particularly well rested as I'd done 4 hours the day before.

    It looks like I'm due some rest days now though. The aluminium bottom bracket sleeve on my 2009 Specialized Epic that the bearings press into has snapped meaning that I need a new frame.

    My New S-work Epic impressions

    I thought I'd have a go at creating a workout in CycleOps Poweragent for the Joule 2.0 to do on the turbo trainer. If you're using the Joule 2.0 computer without a power meter connected then the workout feature is useless unfortunately. The only measurement you can use to create sections within workouts is power. It's not possible to make a workout based on any other measurement such as speed, cadence or heart rate.

    When you start the workout on the Joule 2.0 head unit all that is shown is the target wattage range and the watt power display. It's possible to cycle through to the normal dashboard that displays other information besides power but then you can't see countdown timer or target range.

    I ended up using my Polar RS800CX for the turbo trainer session instead because with that you can use heart rate zones to set out the workout schedule properly.

    Pictured below: When creating a workout schedule for the Joule 2.0 you can only use Power as a measurement and options are very limited.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-joule_workout.jpg  

    Last edited by WR304; 11-07-2010 at 03:44 PM.

  72. #72
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    One major reason for going for the Joule 2.0 computer was because I hoped that it would be more accurate and reliable when recording data than a Garmin.

    Along with just looking at recorded ride data in a graph or WKO+ report it's useful to be able to export the raw data into a program such as Microsoft Excel so that you can look at a particular aspect in more depth and create your own reports. One example of that is using the 1 second recorded speed data to evaluate your braking deceleration on descents.

    My New S-work Epic impressions

    If you open Joule 2.0 ride data in WKO+ 3.0 then the "raw data" view (select 1-2-3 from the top bar) allows you to see the data in 1 second steps. The columns displayed in WKO+ include altitude and temperature. These can be manually edited one cell at a time but you can't copy to the Windows clipboard and export what you see on the screen directly to Microsoft Excel.

    Instead you have to use the File - Save Copy As option and create a .csv file. This .csv file is interesting because the format must be for the older yellow Powertap headunit. When you export the data altitude and temperature are missing from the new .csv file. This happens with both Poweragent 7.5.1.19 and WKO+ 3.0 build 47. What I'd hoped to be able to do was export the data, manually correct the false altitude readings of the Joule 2.0 and then re-import the correct data.

    There are some other things worth mentioning when you look at the exported files. The time field of the exported data is expressed in minutes for some reason. Each cell is one second though so you could just fill it down with a series.

    At least power, heart rate, speed and cadence are the same between the software and export files which is something. Distance works out overall but distance in "raw data" view of WKO+ refuses to be anything but miles for this file. It must be a bug in WKO+ as this one doesn't change. It's somehow ended up with distance in miles but then speed in kph.

    The Torque value (Hub Torque in WKO+) manages to be different depending upon whether you look at the Poweragent software, WKO+ or the .csv export from WKO+ into Excel. This is another column that appears buggy. At least one of the headings is wrong. If you do the conversion (1 pound inch = 0.11298482933 newton meter) then Hub Torque (lb-in for WKO+) equals Torque (N-m) in the WKO+ .csv file. But then WKO+'s lb-in torque figure equals the torque N-m figure in the Poweragent .csv file...

    http://www.onlineconversion.com/torque.htm

    What there needs to be is a way to just export the "raw data" straight from WKO+.

    Pictured below: Joule 2.0 data as viewed in WKO+ 3.0 "raw data" view shows all the fields and data available in a list format.
    The same Joule 2.0 data is then exported as a .csv file from both WKO+ and PowerAgent and opened alongside each other in Microsoft Excel. Note the differences in rounding between the two files, the missing fields and also how the Torque values manage to be completely different between all three sets of data.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-joule_wko_data_as_viewed.jpg  

    PowerTap Disc-joule_wko_data_export.jpg  

    Last edited by WR304; 11-09-2010 at 12:53 PM.

  73. #73
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    Quote Originally Posted by WR304
    I've been trying to compare the Powertap recorded data to what was produced by my Polar RS800CX which recorded heart rate, speed, cadence and altitude. There are a few interesting differences that I've been trying to understand why they're happening. The main one is that the distance recorded by the Joule 2.0 (with Powertap hub) is reading higher than the Polar by about 1.4% when both were using the same tyre and identical circumference measurement.
    It took me a while but I've finally worked out why the distance recorded by the Joule 2.0 (with Powertap hub) and Polar RS800CX is different when using the same tyre and the same circumference measurement.

    The reason is that the Polar RS800CX speed sensor was mounted on the front wheel. It measures rotation of the front wheel/ tyre whilst the Joule 2.0 measures rotation of the rear wheel/ tyre via the Powertap.

    My tyre circumference was reached by rolling the bike alongside a tape measure for one wheel rotation. Although the front and rear tyres may have the same circumference in a static rollout measurement their circumference whilst riding will be smaller than this measurement. When you sit on the bike and ride your weight compresses the tyres slightly making the riding tyre circumference smaller than the static tyre circumference measured on a tape measure. There's always going to be a difference between the static and riding circumference of the wheels.

    The two tyres don't compress equally. When riding significantly more rider weight is on the rear tyre than the front tyre which compresses it slightly more than the front tyre. This means that the rear tyre will have a smaller circumference than the front tyre. Over the course of a ride the front and rear wheels don't rotate exactly the same number of times. This is what causes the difference in distance between the two computers where one is counting front wheel rotations and one is counting rotations from the slightly smaller rear wheel.

    If the tyre circumference entered in the computer is larger than the actual wheel circumference then it means your distance travelled and average speed will be artificially inflated. This matters more when distance/ speed is calculated from the rear wheel than from the front wheel because of the increased difference between the static circumference of the rear tyre compared to the smaller compressed riding circumference of the rear tyre. There's less of a difference between the front tyre's static and riding circumference so it doesn't create quite as large an error.

    This is actually quite an important point because it means that when using a Powertap hub to measure speed/ distance you can't safely use the static tyre circumference. If you do then all your speed/ distance data will be inflated when compared to the distance that you actually travelled, and by a greater amount than if you were using a front wheel speed sensor.

    The solution is to measure the actual riding circumference of the rear tyre. In order to do this you put a single spot of something that will leave a clear mark on the ground onto the tyre with each tyre rotation (eg: a blob of white grease), ride along seated in a straight line for a few metres and then measure the distance between blobs left on the ground. The distance between two blobs is the riding circumference of the tyre which you can then use as the wheel circumference figure in your computer for a more accurate speed/ distance reading.
    Last edited by WR304; 11-14-2010 at 04:46 PM.

  74. #74
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    I ran into an issue with the Joule 2.0 head unit that I haven't read about anywhere. Managing to corrupt the ride data was a bit of a surprise.

    Data recording on the Joule 2.0 head unit can't be stopped or started manually. It automatically begins and pauses recording when either speed or heart rate is registered. I have it set to auto start/ pause on speed. The last time I used the unit was a few weeks ago. At the end of that ride I stopped at the top of the drive and pressed "Stop and save ride" which creates a new data file and resets all the onscreen totals so that the display reads zero for elapsed time and distance. After resetting the head unit I then pushed the bike from the top of the drive to the house.

    During this time the wheel obviously span fast enough to register and add 2 seconds to the timer. The bike then sat unused for several weeks due to the frame breaking and then the snowy weather. After those weeks I finally got to ride outdoors and didn't think to reset the timer first. 2 seconds doesn't make much difference to the average speed. When I finished the 3 hour ride I saved the file and connected the head unit to the PC to import the file.

    The file had the date from several weeks ago and a ride time of 4 seconds. What had happened was that the file had begun weeks ago, but the overall time kept increasing whilst the head unit sat in a drawer paused. The unit keeps track of both moving time (2 seconds) but also stationary time. That stationary time had become so large (hundreds of hours) that it couldn't deal with it anymore. So long as you remember to reset the recording before every ride then this problem won't happen. Forgetting to reset the recording is an easy mistake to make as there's no indication on the display that it's doing this

    Exporting the data to a .csv file showed the first few seconds were ok but then every other time entry had become 4 seconds. The distance and speed data was still intact so it was possible to repair the file. This meant it was possible to recover the data. In order to do this you need to overwrite the corrupt time data with the correct time data. With a Powertap the head unit records at one second intervals so each cell in the .csv file represents one second. The .csv file expresses the elapsed time in minutes so each second is 1/60 = 0.01666 recurring.

    Step 1 - Make sure that cell A2 is 0.01666 recurring.
    Step 2 - In Microsoft Excel next highlight only the cells of the time column of the .csv file which have data in and select Fill- Series.
    Step 3 - In the step dialog box enter 0.01666 recurring (copy and paste from a cell for more decimal places) and press ok. This will make each data cell increase by 0.01666 (one second).
    Step 4 - Save the file as a .csv with a new name.
    Step 5 - Re-import the file into WKO+ or Poweragent by selecting File- Open Workout within WKO+ and browsing to the new .csv file. If it looks ok select your user from the Workout settings list, select the correct date, enter the ride details and press save to update your new file.

    I've tried to go into some detail about fixing the file because this is a really easy mistake to make if you forget to reset the head unit.

    Pictured below: Using Fill - Series in Microsoft Excel to repair corrupt Joule 2.0 data in a .csv file
    Attached Thumbnails Attached Thumbnails PowerTap Disc-joule_data_repair_excel.jpg  


  75. #75
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    This Youtube video is where DC Rainmaker tests the weatherproofing of several power meter head units: The Garmin Edge 800, Garmin Edge 500, Garmin Edge 705 and Cycleops Joule 2.0. They seem to fare quite well.

    http://www.dcrainmaker.com/2010/12/f...ion-tests.html

    <object width="640" height="385"><param name="movie" value="http://www.youtube.com/v/_iS7TtUmJmY?fs=1&amp;hl=en_GB"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/_iS7TtUmJmY?fs=1&amp;hl=en_GB" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="640" height="385"></embed></object>

    My Powertap has mostly been working ok. I've been concentrating on short 2 - 2.5hr rides at the moment with some intervals built in whilst trying to keep the intensity factor high. What I'm liking about the power meter is that it lets you compare rides on an "apples to apples" basis. A good example is being able to look at current rides when the bike has offroad tyres fitted and still directly compare the power output to the rides on slick tyres that I did in November 2010.

    For doing intervals the power meter shows just how inconsistent my pacing during intervals can be. The power outputs below being a set of 6 x 4 minute intervals outdoors from the other day. They all felt hard when I was doing them but looking at the recorded data the power output was erratic. It's something to work on improving.

    Interval 1: 226 watts
    Interval 2: 205 watts
    Interval 3: 217 watts
    Interval 4: 199 watts
    Interval 5: 205 watts
    Interval 6: 224 watts

    The Powertap hub hasn't done many miles but I've been having a few data drop outs like the one pictured below. I'm wondering if maybe it had been sat on a shelf for a long time and could do with some fresh batteries already?

    Pictured below: Powertap Data Drop Out
    Attached Thumbnails Attached Thumbnails PowerTap Disc-powertap_data_drop_out.jpg  

    Last edited by WR304; 01-13-2011 at 02:45 PM.

  76. #76
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    I'm a training with power newbie (I do not have a power meter) but I have a question - does the power tap give you an upsift or down shift based on your altitude / hr / current power output?

  77. #77
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    Quote Originally Posted by Litemike
    I'm a training with power newbie (I do not have a power meter) but I have a question - does the power tap give you an upshift or down shift based on your altitude / hr / current power output?
    I'm not sure what you mean by upshift or down shift in terms of a power meter?

    No current power meter head units are linked into the bicycle's gears. It's not like the Shimano Flightdeck computer which displays what gear you're in on the screen of the bike computer whilst riding.

    You can estimate where you changed gear from changes in cadence and power output when looking at the graph post ride. It's actually easier from the cadence trace than power though. Spikes in cadence often signify a downshift whilst a drop in cadence followed by an increase in power can mean an upshift. The Powertap virtual cadence isn't that accurate however. It's much easier to look at with a proper cadence sensor that actually counts crank rotations.
    Last edited by WR304; 01-14-2011 at 04:54 PM.

  78. #78
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    One solution to getting upshifts and downshift is to use the Gears plugin for SportTracks. After configuring your wheelsize and gear ratios, it does a very good job of reproducing your gearing for a ride! Of course you need a cadence sensor and it'S only available post ride.

    I use it somewhat often with my Filtered Stats plugin to find where I used certain gears (ie little ring)
    Check out my SportTracks plugins for some training aid software.

  79. #79
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    I thought you might be interested in some power output comparisons between October 2010 and mid January 2011.

    With a power meter it's possible to evaluate what sort of performance decrease 6 weeks of limited cycling can have on power output, and also how long it may take for power output to return to the same levels again when training is resumed. October 2010 wasn't my best month of last year, but I was quite fit and is the earliest that I have any power data for. Weight stayed stable at 154lbs.

    Mid November 2010 and all of December 2010 were a complete disaster in terms of cycling. My bike broke, then it snowed and I also managed to catch flu over the Christmas period. That meant I did hardly any cycling during that period - some turbo training intervals and a bit of weight training but not much (8 hours total in December). There must have been some detraining during that time.

    The table below shows the best 1 minute, 5 minute, 20 minute and 60 minute power output numbers for October 2010 and then the best power output numbers for each week of 2011. The red numbers are the shortfall in power output for 2011 compared to October 2010. It shows that I lost a significant amount of power from the 6 weeks of limited riding. A few weeks of solid riding has seen the power numbers begin to improve rapidly again though. Whether that will keep going or begin to plateau still has to be seen.

    Calculating a reasonable FTP figure (best 1 hour time trial pace) is still proving difficult. I've been using 220 watts for now as I suspect that I could possibly do that for an hour if I was pushed hard enough in a race situation. As you can see from the table I'm getting nowhere near that hourly power output in normal riding, even doing short hard rides, so possibly I should be using a lower FTP? The problem is identifying the gap between what I'm doing currently and what I can actually manage.

    This thread on the subject is worth looking at:

    http://www.cyclingforums.com/forum/t...d-1-hour-power

    Pictured below: My best Power output numbers for October 2010 compared to the first weeks of January 2011. Edited to add the TSS figures for January 2011. I didn't have a powermeter for all October 2010. The one week I did with the Power meter in 2010 had a TSS of 1,234 but that was spread over 18 hours of riding.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-detraining_retraining_2010_jan_2011.jpg  

    Last edited by WR304; 01-18-2011 at 11:11 AM.

  80. #80
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    Quote Originally Posted by WR304
    The Powertap hub hasn't done many miles but I've been having a few data drop outs like the one pictured below. I'm wondering if maybe it had been sat on a shelf for a long time and could do with some fresh batteries already?
    The drop outs have been getting increasingly frequent so it looks like the hub batteries are going. There were several in today's ride so I'm going to try replacing the batteries with new ones. The batteries needed for the Powertap hub are:

    2 x 357 batteries for the hub

    Something that's good with the Powertap is that when riding you can clearly tell when you're tired because it's so difficult to sustain the required power output. Today was a good example:

    It was a nice day so I thought I'd do a longer ride but with a few intervals and hills thrown in to make it more challenging. I manage the first few intervals ok but after just 50 minutes into the ride I'm cooked. This was very obvious from how the power output was falling away. Not great when there was still another 2h40 of riding and all the major climbs still to come.

    Looking at the downloaded data post ride the first 50 minutes of the ride was at an average of 187 watts but then the rest of the ride was a much lower average of 155 watts. Time for a day off.
    Last edited by WR304; 01-21-2011 at 02:59 PM.

  81. #81
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    Quote Originally Posted by WR304
    The drop outs have been getting increasingly frequent so it looks like the hub batteries are going. There were several in today's ride so I'm going to try replacing the batteries with new ones. The batteries needed for the Powertap hub are:

    2 x 357 batteries for the hub
    I replaced the batteries in the Powertap hub and it looks like that was the problem. There were no data drop outs at all in today's ride.

    The original batteries only lasted for approximately 60 hours of riding. I'm hoping that starting with fresh batteries means the hub will last a bit longer before they need replacing again.

    One thing that's really annoying me is the barometric altimeter on the Cycleops Joule 2.0 head unit. There was about a week where the outdoors temperature increased and the altimeter recorded positive altitude values. The outdoors temperature has dropped back down towards 0c and the altimeter is at -572 feet again. As it can't be calibrated to the correct starting point that means no altitude data is viewable in WKO+, even for the hilly rides.

    I've been seriously thinking about getting a Garmin Edge 800 as a replacement but all the threads about corrupt Garmin Edge 800 .fit data files which can't be uploaded, loss of connection to Powertap hubs, cracked touch screens etc have me wondering whether it would actually be any better than the Joule 2.0.

    Garmin Edge 800 corrupt data
    https://forums.garmin.com//showthread.php?t=15674

    Garmin Edge 800 loss of connection to Powertap hub
    https://forums.garmin.com//showthread.php?t=15826

    Garmin Edge 800 cracked touch screen
    https://forums.garmin.com//showthread.php?t=14493

  82. #82
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    I love my Edge 705, couldn't it be a good alternative? The 800 doesn't have that many interesting new features honestly.

    Quote Originally Posted by WR304
    I replaced the batteries in the Powertap hub and it looks like that was the problem. There were no data drop outs at all in today's ride.

    The original batteries only lasted for approximately 60 hours of riding. I'm hoping that starting with fresh batteries means the hub will last a bit longer before they need replacing again.

    One thing that's really annoying me is the barometric altimeter on the Cycleops Joule 2.0 head unit. There was about a week where the outdoors temperature increased and the altimeter recorded positive altitude values. The outdoors temperature has dropped back down towards 0c and the altimeter is at -572 feet again. As it can't be calibrated to the correct starting point that means no altitude data is viewable in WKO+, even for the hilly rides.

    I've been seriously thinking about getting a Garmin Edge 800 as a replacement but all the threads about corrupt Garmin Edge 800 .fit data files which can't be uploaded, loss of connection to Powertap hubs, cracked touch screens etc have me wondering whether it would actually be any better than the Joule 2.0.

    Garmin Edge 800 corrupt data
    https://forums.garmin.com//showthread.php?t=15674

    Garmin Edge 800 loss of connection to Powertap hub
    https://forums.garmin.com//showthread.php?t=15826

    Garmin Edge 800 cracked touch screen
    https://forums.garmin.com//showthread.php?t=14493
    Check out my SportTracks plugins for some training aid software.

  83. #83
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    Quote Originally Posted by WR304
    The drop outs have been getting increasingly frequent so it looks like the hub batteries are going. There were several in today's ride so I'm going to try replacing the batteries with new ones. The batteries needed for the Powertap hub are:

    2 x 357 batteries for the hub

    The ability to replace the batteries in a Powertap is the reason they are superior to SRMs. You have to send SRMs away to get the batteries replaced, which
    a) Takes a fair bit of time
    b) Is stupidly expensive ($200+)
    c) The north american company that does it, isn't very good at calibrating them.
    "The best pace is suicide pace, and today is a good day to die." Steve Prefontaine

  84. #84
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    Quote Originally Posted by LMN
    The ability to replace the batteries in a Powertap is the reason they are superior to SRMs.
    Doesn't Alison's husband work for SRM now? Maybe you could get him to work on that...?
    Tire Design & Development Engineer. The opinions expressed in this forum are solely my own.

  85. #85
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    When quarq comes out with a mountain option, I will probably go that route. My road version is about 3 weeks out. very excited.
    Stand For Something.

  86. #86
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    And I know this is petty but, the edge 500 and 800 win me over due to the mount almost all by itself.

    I just could not stand that sliding clasp thingy on my 705. I broke two of em in frustration trying to get the damn thing off of there.

    The twist mount is infinitely better IMO.
    Stand For Something.

  87. #87
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    Quote Originally Posted by MisterC
    And I know this is petty but, the edge 500 and 800 win me over due to the mount almost all by itself.

    I just could not stand that sliding clasp thingy on my 705. I broke two of em in frustration trying to get the damn thing off of there.

    The twist mount is infinitely better IMO.
    I've been abusing mine (3 on 3 bikes) without a problem for as long as the 705 came out. Some folks are rough with their mounts, I've read numerous stories of them breaking but never understood how they did it.
    Check out my SportTracks plugins for some training aid software.

  88. #88
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    Quote Originally Posted by PissedOffCil
    I love my Edge 705, couldn't it be a good alternative? The 800 doesn't have that many interesting new features honestly.
    I'm dithering badly about what a good power meter head unit option would be. They all seem to have some disadvantages. You don't really know how easy they are to live with until you actually get to try them out.

    The thing I like in theory about the Garmin Edge 800 over the Edge 705 is that it has a touch screen instead of a joystick. The joystick for navigating menus and displays on the Cycleops Joule 2.0 is fiddly and a nightmare to use when wearing winter gloves.

    With devices like these Garmins you're very reliant on firmware updates. When a newer model comes out the older ones often become a lower priority for updates. A newer model seems like it would be more likely to have ongoing support. The argument with the Garmins seems to be that it takes a few years before their products actually work properly.


    Quote Originally Posted by LMN
    The ability to replace the batteries in a Powertap is the reason they are superior to SRMs
    Changing the Powertap hub batteries would be a lot easier if they'd designed the hub so the plastic tool can unscrew the cover without needing to remove the brake rotor first.

    I was a bit hasty thinking the new batteries had solved the issue. There were two dropouts in yesterday's 2h30 ride and three dropouts in today's 2h45 ride so it's still happening. The dropouts appear to be totally random whilst out in the middle of the countryside. I don't know if it's the head unit or the hub? On the plus side the dropouts are all short like the one pictured in post #75 so they're only losing a few seconds of data each time. When riding I'm not noticing the dropouts as they're short gaps. They only show up when reviewing the data post ride.

    One thing I'm trying to understand is why there's a clear gap between my climbing power output and flat power output. It's not the same as Battle Duck's thread because all of my data is whilst riding seated.

    FTP 300 W, 20 min 400 W (standing)

    The two graphs below are extracts from today's ride (The altimeter had gone wrong so there's no altitude data). The seated climb is up a 6.6% average gradient hill. I was using the 23T rotor granny ring. The flat ride section is the final 10 minutes of the same ride home on the 44T round big ring where I was flat out and going as hard as I could. For a similar average heart rate and average cadence I managed 240 watts average climbing but only a poor 215 watts on the flat.

    There's got to be an obvious explanation.

    Pictured below: Differences in seated climbing power output up a 6.6% gradient hill and flat power output from today's ride.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-power_seated_climbing.jpg  


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    Quote Originally Posted by bholwell
    Doesn't Alison's husband work for SRM now? Maybe you could get him to work on that...?

    Ha! No. I don't work for SRM, or any other cycling related company. Wish I could help. I could recommend some good angioplasty catheters though.
    Try to be good.

  90. #90
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    Quote Originally Posted by whybotherme
    Ha! No. I don't work for SRM, or any other cycling related company. Wish I could help. I could recommend some good angioplasty catheters though.
    No, sorry, not you- Alison Dunlap's husband.
    Tire Design & Development Engineer. The opinions expressed in this forum are solely my own.

  91. #91
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    Quote Originally Posted by bholwell
    No, sorry, not you- Alison Dunlap's husband.
    cool. sorry for the confusion.
    Try to be good.

  92. #92
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    One of my big reasons for getting a power meter was for comparing ride intensity and trying to evaluate whether I was tired or not.

    The problem being that after a few weeks of solid riding my exercise heart rate response would be very low, even though I felt good. I'd end up ignoring the heart rate monitor most of the time as I simply didn't believe what it was telling me.

    What's the consensus for measuring power?

    My hope was that the power meter would give a more objective measure that I could rely on. So far this has been working quite well. When riding the drop in performance when you're tired, both in terms of Intensity Factor and average power is very noticeable. A quick glance at the report is all it takes to show which rides were good and which weren't so far this year.

    The WKO+ report below shows the rides that I've done so far in January 2011. The red line is average heart rate whilst the yellow line is average power for the same ride. You can see immediately that most of the rides have been fairly solid, apart from three which have much lower average power. The two days marked with a 1. are active recovery rides, whilst the ride marked with a 2. is the one mentioned in post #80 where I blew up badly. When you view the data in a report these stand out clearly as being different from the others. If you blow up it's reflected in the data.

    I mentioned that I found heart rate an unreliable tracking measure and you can see that pattern emerging here also. For the first week or so the red heart rate line is higher than the average power line, but then the trend reverses mid month and the red heart rate line falls below the average power line. It's most marked at the point marked 3. on the report where I was doing 2h30 each day. My average heart rate per ride drops badly to as low as 148 bpm, even though I'm still feeling ok and able to maintain the average power output of previous rides.

    The Intensity Factor for most rides was in the .85 to .93 range (assuming my FTP is right...) I've left IF off the report below because you can't adjust the axis scales in WKO+ reports. All the different lines and bars end up in a difficult to view mass. It's quite a serious omission from the WKO+ software.

    The power meter is useful for ensuring active recovery rides are in the right zone too. It's all too easy to end up going harder than you'd think. Keeping the power output low enough on an active recovery ride seems to involve bottom gear whenever there's any sort of slope at the moment.

    Pictured below: My Average Power and Average Heart Rate trends for January 2011 so far. It shows that my heart rate and power output aren't always closely related.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-average_power_average_heart_rate24-01-2011.jpg  


  93. #93
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    It's possible to use recorded power data as a way of deciding the best pacing strategy for a ride or climb. Going as hard as possible isn't always the best option.

    Burning "Matches"
    A "match" is an elusive term used by riders, and coaches within the bike racing world. When you burn a match, you have done a hard effort. It's an effort that in which you had to dig deep, or you had to really push yourself.
    ...
    Why do you need to know what a match is? Well, you as a rider, start out the day with a full set of matches in your matchbook, but every time you go hard, do an attack, have to hammer over a hill, you burn one of your matches. All of us have different size matchbooks, but nobody has an infinite number, so it's important to burn your -matches- at the right time during a race or in training. Otherwise you are left with an empty matchbook and then your chances of performing well have been drastically reduced."
    Hunter Allen

    http://www.peaksware.com/articles/cy...ter-allen.aspx

    When reviewing power meter data you can look through and note where the hardest efforts were. A theme in many of my rides was the observation that hard efforts were often followed by a sag in power output as I struggled to recover, losing more time than the hard effort had gained.

    One of the worst of these was part of a short ride that I had done on 13 Jan 2011. I got to the second hill of the day and went hard up the first gentle 5.7% gradient section at 230 watts. The climb then ramps up steeply mid way to 10% gradient. I went up the steep section as hard as I could, peaking at 291 watts for 42 seconds, putting me deeply into the red "anaerobic zone" according to the Coggan power zones. As a result I had to slow down to try and recover. I could only manage 195 watts average power output for the remainder of the climb, which is a 4.5% gradient. It took a long time to recover after the climb also.

    I did the same ride today. Remembering what had happened last time I decided to try a different strategy for the climb. I could see from the power data that the steep section looked like I'd burned a "match" as the 291 watts power output was 132% of my (estimated) 220 watts FTP. This time I decided to try and pace myself up the steepest section using the power meter instead of going flat out. I knew I'd lose some time on the steep section but hopefully make it back later.

    Comparing Climbing Pacing Strategies
    The graph below shows the climbing power output from 13 Jan 2011 (magenta) overlaid with the climbing power output from 25 Jan 2011 (yellow). It's easier to see if you zoom the picture in your browser.

    The four dotted lines are the edges of the different power zones. Anything above the upper dotted line is "anaerobic zone". The first section of the climb is highlighted in green. I rode the lower section of the climb at a similar average power output on both days. 13 Jan 2011 was slightly quicker here because I carried more speed through the bend that leads onto the climb.

    The steepest section of the climb is very different however. Instead of going competely flat out I used a lower gear. I was still trying hard but only in the "anaerobic zone" for 19 seconds at 272 watts. Half the time when compared to 13 Jan 2011. I was only 4 seconds slower too despite riding at a lower intensity!

    The benefits of this approach are apparent in the time and power output for the top section of the climb where I was able to maintain the power output at 232 watts on 25 Jan 2011 as opposed to 195 watts (and struggling) for the same section on 13 Jan 2011.

    I was also able to recover quicker after the climb and keep the pace high for the rest of the ride. The final totals for the entire ride being 1h 36 min at an average of 188 watts for 13 Jan 2011. 25 Jan 2011 was 1h 34 min and 36 sec at an average of 200 watts. All that time difference was gained in the section of ride after the climb pictured below as I felt able to keep pushing. The two rides had been very even until then.

    Pictured below: Variations in pacing when climbing on two different days. Yellow is 25 Jan 2011, Magenta is 13 Jan 2011. Zooming the picture in your browser makes it easier to see both traces.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-pacing_varying_gradient_climb.jpg  

    Last edited by WR304; 01-26-2011 at 10:56 AM.

  94. #94
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    I've been trying to compare the energy expenditure (kilojoules) as calculated by my Powertap with the energy expenditure (kilo calories) that was calculated by my Polar RS800CX heart rate monitor. I wanted to see how comparable the energy expenditure calculation was between the two devices. In theory you can simply say that 1 kilojoule measured by the power meter is equal to 1 kilo calorie because of efficiency losses (instead of converting the kilojoules into calories).

    The kilo calories burnt calculation of a heart rate monitor is highly reliant on the initial user values that you enter into the heart rate monitor (age, weight, exercise level, Max HR, VO2 Max etc.) The energy expenditure is then estimated using a formula based on these values. As a result the kilo calories burnt figure calculated using a heart rate monitor can be wildly inaccurate - often over estimating the numbers of calories burnt.

    Have a read of this web page and try out the calculator to see how the estimated kilo calorie usage numbers change when you use different VO2 Max and age values (age in this formula adjusts your maximum heart rate). If you use an estimated maximum heart rate and estimated VO2 Max for the settings (as opposed to knowing your actual maximum heart rate and having a lab tested VO2 Max) then it introduces errors into how the heart rate monitor calculates energy expenditure.

    Calorie Expenditure Calculator:
    http://www.braydenwm.com/calburn.htm

    Whilst I was looking at various articles the interview discussing energy expenditure below was linked. I've posted it here because it seems relevant when considering what a Powertap can be useful for.

    Full Discussion:
    http://www.bikeforums.net/showthread...urned-seem-low

    ************************************************** ************************************************
    Energy In, Energy Out: What's the Magic Equation? (Part I)

    A few weeks ago I was going through a thread on slowtwitch.com discussing caloric expenditure on the bike and the accuracy of the kcal numbers on our HRM’s. I always assumed that the variables in caloric expenditure could never be accurately determined by heart rate alone; temperature, hydration, force, etc all have a direct effect on energy needs, right? In order to get a better understanding on our energy needs I contacted Richard Stern*, cycling and multisport coach of cyclecoach.com, Gordo Byrn of coachgordo.com, and my coach, Lauren Maule.

    I’ll begin this series with Richard. Reading his in depth explanations on the slowtwitch thread - "Fat loss question" are what set me on this quest. I began my inquiry by asking Ric simply, why is the Polar computer inaccurate and by how much?

    Stern: Energy Expenditure (EE) is related to power output, as EE = power x time. This is actually the mechanical energy used to drive the bike but is actually close enough to actual EE. The mechanical energy is actually in kj (kilojules), but can be converted to kcal (kilo calories) -- the more usual metric for nutrition.

    Supposing, that a cyclist averaged 200 watts (W) for 3-hours, the mechanical energy (ME) would be: ME = power (/1000) x time (secs) = (200/1000) x (3 x 3600) = 0.2 x 10800 = 2160 kj

    However, 1 kcal is equal to 4.18 kj, thus, 2160 kj is equal to 517 kcal. Obviously, this would be a very low EE for a 3-hr ride. Interestingly, efficiency during cycling is ~ 20 - 25% in trained riders, so these two figures approximately cancel, and we can then say that 2160 kj ride is approximately a 2160 kcal ride.

    Efficiency (thermodynamic efficiency), is a measure of the actual mechanical work accomplished divided by the input of energy. This is mainly affected by cadence in cycling. Paradoxically, efficiency is *highest* at lower cadences, and lower at higher cadences. This is because energy is required to just move the legs (with example, no chain on the bike) and higher cadences require more energy. However, as power output increases, efficiency also increases. Therefore, topographical conditions have an effect on efficiency as you tend to pedal slower uphill and faster on the flat.

    The biggest retarding force in cycling is air drag (hence the reason why we all try to get as aero as possible). If for example, you have two bikes a TT aero one, and a standard road bike, at the same speed under the same environmental and topographical conditions you'll need to produce less power on the TT bike than the road bike.

    Heart rate can vary for a multitude of reasons, e.g., temperature, topographical conditions, humidity, fatigue, stress, caffeine, etc. Heart rate can vary quite dramatically even at a constant power output. As an example, when I complete 20-min TT intervals at the same power (ridden indoors on a trainer) my HR can vary by ~ 15 to 20 b/min depending on the session the day before, what I've done just before, fatigue, etc. Heart rate therefore becomes 'unreliable'.

    Therefore, knowing power is the only realistic way of calculating energy expenditure, as trying to estimate it EE from e.g., HR is just too variable. Thus a HR monitor won't give an accurate or useable EE for cycling as there are too many variables not accounted for.

    KP: Without the benefit of having a power meter, how can one assess their caloric expenditure while cycling (assuming they use an HRM)?

    Stern: Basically, unless you want to do a reasonable amount of analysis it's pretty much impossible to estimate EE without a power meter, and get a meaningful answer.

    KP: I read on Gordo's site that Molina is of the opinion that the average well trained athlete burns 100 kcal per mile and an elite runner could burn as little as 50 per mile. Do you agree? Can you speculate on how this translates with swimming?
    Stern: It's generally easier to calculate EE in running because speed varies less than in cycling and position isn't as important. However, running economy does vary between individuals.

    KP: What do you suggest for your cycling and multisport athletes that you coach who lack power meters?
    Stern: I don't suggest that they attempt to track EE. It would be very unreliable data.

    KP: Do the foods consumed and their micronutrient content affect the balance of fat used to other fuel sources? How can one maximize fat usage as opposed to glycogen and protein?

    Stern: Other than by training and getting fitter (i.e., increased VO2 max, increased LT) there is little or nothing that can be done to affect substrate usage. As we get fitter, we use more fat at a given intensity compared to glycogen. As the duration increases there can be a shift to greater fat usage. As relative intensity increases there's a greater use of muscle and liver glycogen (i.e., for an Olympic/sprint you'll be exercising at a higher intensity than an Ironman distance event, and using more carbohydrates).

    During exercise, it's important to keep taking in carbohydrates and fluids. There's unequivocal evidence to support the use of carbohydrate during events longer than one hour (and some evidence for less than one hour). Taking in 0.7 g carbohydrate / kg body mass has been shown to unequivocally extend performance (e.g., 30 to 60 g / hr).

    During exercise fluid intake is crucial to prevent dehydration: this can be achieved with 150 - 350 mL (milliliters) of a carbohydrate-electrolyte solution every 15 - 20-mins, starting at the beginning of exercise. The carbohydrate-electrolyte solution should be 4 to 8% and contain sodium. The electrolytes stimulate the thirst mechanism and can help prevent hyponatraemia in susceptible people.

    KP: Can one determine optimal power to weight ratio without a power meter? Some try so vehemently to lose weight they end up costing themselves power in the process. Can one determine their optimal power to weight ratio by doing say, a specified hill or TT course over a period of weeks and comparing weight, time's, effort level, and HR?

    Stern: Within the confines of losing typically small amounts of mass (e.g., ~1 or 2 kg) it will make little or no difference to performance. Unless you have a large amount of fat to loose, then it's virtually always better and easier to gain power compared to losing weight (as a primary goal). In fact, with a lot of the riders that I coach, whilst training intensely for increases in e.g., LT power output or power at VO2 max, they end up losing some fat due to the increased training energy expenditure. During flat ground cycling there's little to be gained by loosing small amounts of weight and even on hills it will only add a very small amount of time. Power to mass ratio is of more importance when e.g., cycling uphill.

    More to follow in the next installment.

    *Richard Stern is a cycling/multisport coach in UK and retains the copyright on the material used in this interview. For more information, visit www.cyclecoach.com or click on the banner below.

    ************************************************** *************************************************

    .
    Last edited by WR304; 01-26-2011 at 03:40 PM.

  95. #95
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    There was a short article about the Fisica ANT+ sensor key on the DC Rainmaker blog.

    It lets you use ANT+ to connect sensors such as the Powertap hub to your iphone or ipad and use it as a head unit.

    http://www.dcrainmaker.com/2011/01/w...ng-update.html

    http://www.dcrainmaker.com/2010/05/f...nt-iphone.html

    http://www.wahoofitness.com/Fisica/W...Sensor-Key.asp

    The example was of overlaying your live power data on the screen with a video. It might be interesting if you do a lot of indoor training and want some extra motivation.

    Pictured below: DC Rainmaker live power data overlaid on a ipad.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-ipad_powermeter.jpg  


  96. #96
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    Quote Originally Posted by WR304
    One of my big reasons for getting a power meter was for comparing ride intensity and trying to evaluate whether I was tired or not.

    The problem being that after a few weeks of solid riding my exercise heart rate response would be very low, even though I felt good. I'd end up ignoring the heart rate monitor most of the time as I simply didn't believe what it was telling me.
    A lot of the things which I'm finding when riding with a power meter appear fairly obvious. What it does is provide the supporting information to actually prove it either way - whether I really was being lazy and riding around at a low intensity as the heart rate monitor was saying, or whether I was trying hard like my perceived exertion indicated.

    The graph below is an updated version of the chart from my earlier post. This one has the rides grouped into weekly blocks and is up to 30 January 2011 for five full weeks. This style of report hides the detail of individual days but it does give an overview of how my heart rate and power output has changed over the month. It appears to largely confirm what I'd suspected - that even when my heart rate response is low I can still have good pace, be trying hard and improving.

    In the final week of January 2011 I set my best peak power records (for January) at 5 seconds, 1 minute, 20 minutes and 60 minutes which was encouraging. Without Monday's active recovery ride included the final week to 30 January 2011 was also the best overall (178 watts average, 146 bpm heart rate and an IF of 0.87 for 11h 45 min!). It's still a way off October 2010 but shows progress.

    At the same time however my average heart rate has fallen significantly over the same period - from an average of 166 bpm in the first full week of January 2011 to an average of 144 bpm in the final week of January 2011. If you were looking purely at the WKO+ heart rate zone summaries for the last few weeks then you'd conclude that I'd just been doing lots of long steady distance riding without any intensity, which is a misleading picture.

    I need to sort out what my real FTP is though. I'm still using 220 watts for the FTP figure used to calculate these IF and TSS figures. I think it may need revising upwards for February. I'm nowhere near being able to manage even 220 watts for a full hour in actual riding though. The best I've managed so far this year was an average of 202 watts for an hour.

    Pictured below: My weekly totals for average power and average heart rate to 30 January 2011. The power output stays constant but heart rate falls steeply.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-averagepowervsaverageheartrate30-01-2011.jpg  

    Last edited by WR304; 01-31-2011 at 06:23 AM.

  97. #97
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    I am in the prosess of buying a powertap for my road bike.

    Am I wrong in thinking the functions on the SL+ and Pro+ are the same but the SL+ is carbon/lighter? I already have a garmin 500, so i`m just looking at hubs.

    I have both 26 and 29 inch wheels on my MTB`s and most of my intervals are done on the road so I think that is the best option for me.

    I train watt on my fortius in the winter and would like to do it outdoors during the season too.

    There is a lot of cool info been posted up in this thread and i`m looking for a nice gift from my wife for my 40th birthday this year.
    Disclaimer. I now sell bicycles and bicycle tyres.

    instacrap ----> http://instagram.com/manx71/

  98. #98
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    Quote Originally Posted by fux
    I am in the prosess of buying a powertap for my road bike.

    Am I wrong in thinking the functions on the SL+ and Pro+ are the same but the SL+ is carbon/lighter?
    Marginally lighter, that's the difference. I got the Pro+ because it's a training wheel after all.
    Check out my SportTracks plugins for some training aid software.

  99. #99
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    Thanx, Pro+ it is then.
    Disclaimer. I now sell bicycles and bicycle tyres.

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  100. #100
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    Quote Originally Posted by fux
    I am in the prosess of buying a powertap for my road bike.

    Am I wrong in thinking the functions on the SL+ and Pro+ are the same but the SL+ is carbon/lighter? I already have a garmin 500, so i`m just looking at hubs.
    You currently don't get a choice of models for the MTB Powertap. The only option is the most expensive SL+ if you use disc brakes.

    The difference in price between the new Powertap road models appears to be purely down to differing construction and materials used. You're paying for a part carbon hub body and alloy axle / freehub, rather than different internal electronics.

    http://www.cycleops.com/products/power-meters.html

    Road Powertap SL+
    •15mm Alloy axle and free hub body
    •Carbon/alloy hubshell
    •Hub weighs 412 grams

    Road Powertap Pro+
    •15mm Alloy axle and free hub body
    •Alloy hubshell
    •Hub weighs 466 grams

    Road Powertap Elite+
    •15mm Steel axle and free hub body.
    •Alloy hubshell.
    •Hub weighs 583 grams

    If you're looking at road Powertaps for a training wheel then I think I'd choose the Powertap Elite+. The reason being that it has a steel freehub body which will be more reliable as it won't be damaged by Shimano cassette splines. Weight doesn't really matter for a training wheel.

    The MTB disc version of the Powertap SL+ hub has a steel freehub body according to the product page:

    MTB Powertap Disc SL+
    •Alloy axle with steel freehub body
    •Carbon/alloy hubshell
    •Hub with rotor weighs 680 grams

    There doesn't seem to be any difference in the number of strain gauges or accuracy between the different wireless Powertap hubs. (+/-1.5% claimed accuracy for the newer Powertap hubs.) So far as I can tell there's no difference between the data accuracy whether it is recorded by a SL+, Pro+ or Elite+ hub.

    If you were looking at SRM crank power meters then they have different numbers of strain gauges in different models. It makes the more expensive SRM models more accurate, adding something besides just different weights.

    Powertap Accuracy (2005)
    http://www.active.com/cycling/Articl..._are_they_.htm

    Powertap Accuracy (updated January 2011)
    http://biketechreview.com/reviews/po...review?start=1

    .

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