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Big Discrepancy In Today's Bike Test #s (Powertap vs CompuTrainer)

QuintanaRoosterQuintanaRooster
in General Training Discussions

I did the bike test according to protocol and 12 minutes into my warm-up, I calibrated my CompuTrainer.  The numbers don't make sense to me when I compare the data from my Garmin 500 to the data from the CT.  Here's the #s:

1.  CompuTrainer:  distance covered 14.26 miles, avg watts 235, avg speed 20.4 mph

2.  Powertap:  distance covered 15.6 miles, avg watts 202, avg speed 22.2 mph

The numbers don't make sense to me.  Anyone care to offer their analysis?

Comments

  • bconway6650bconway6650
    That's a bummer that you ended up with such a big discrepency. Certainly one of your power measuring devices wasn't properly calibrated throughout your test.

    Do you own the computrainer that you tested on? If so, have you been comfortable with it's accuracy/repeatibility up until now?

    FWIW I go with the computrainer number when I'm going to be trapped indoors on the trainer for an extended time.
  • Chris M.Chris M.

    Saw your post on ST regarding this.  Since your baseline was done on the CT, then just continue to use the CT number, in which case you gained 15 watts!

    Also, PowerAgent is a free download from cycleops.com and if you need help determining your NP from that just let me know.  Send me a PM here or an email to cmartin911 at mac dot com

  • deleshdelesh
    I had a big discrepancy with my computrainer and powertap and it turned out to be that I didn't calibrate my powertap. Now I do the calibration before every workout just to make sure they are "close". They still have a slight difference, but the difference is always constant.
  • Chris GChris G

     Agree that is sounds like something was not calibrated correctly.  Have you watched the power webinar?  Once you are done with that look for the stuff in the wiki.  Rich has written extensively about how to use at computrainer as a training "venue" in comparison to you main power meter.  Read all of that as well.  

    What you are going to find is that --- assuming that both devices actually are working correctly --- that it really does not matter which one you use.  Those numbers look like raw data to me as well?  do you have wko plus?  If not, fix that.

  • Nemo BrauchNemo Brauch
    Just another thought. Avg watts is not quite the same as NP. And you may have the PowerTap/Garmin including 0's in the Avg Watts number while the Computrainer is excluding them (I don't have a CT, so I'm not exactly sure how that setup works).

    My point is, it's also possible both units are calculating and displaying "Average" using slightly different equations.
  • kjanracingkjanracing
    I have a pretty old Computrainer and the Powertap reads way lower, despite both being calibrated. I think the power unit of the CT messes with the wireless signal of the Powertap. I've been doing the workouts on eMotion rollers and both the Powertap and Polar power meter read pretty much the same. I just got a SRM for my bike and i hope to get that set up in a couple days and I'll then see how it and the CT compare.
  • Coach PatrickCoach Patrick
    @Robert, lots of great replies to you here...hope they helped you out!
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