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Computrainer watts muchi higher than PT

sgordon7334sgordon7334
in General Training Discussions

I searched the old forums but didn't see anyone else with this question/issue.  I've ridden my CT for years and watched my watts on it in order to get my FTP and training rides.  

Recently I obtained a PT and am riding that on my CT for the training rides.  What I've noticed is about a ~ 30w difference in numbers, the PT is much lower than the CT numbers I see.  I do callibrate my CT each ride as well as track HR on both PT and CT of which HR is +/- 3 beats so I know that part is working fine.

Has anyone else experienced this issue and how did you resolve it?

One option I have is to bundle up and head outdoors for a ride and go by perceived effort to validate.

Anyone else have a suggestion, advice or can point me in a direction to figure this out?

Thanks

Steve

Comments

  • manconamancona

    Steve, unfortunately different power meters just read differently sometimes for a number of factors.  For example my PT typically reads about 5-10 watts higher than my Computrainer.  I've also heard many cases of SRMs or Quarqs reading slightly higher than powertaps because of where they measure the power at and drivetrain loss.  In fact, two powertaps can even read differently.

    All you really need to worry about is using one that is consitant and accurate day to day compared to itself.  Therefore you should pick one and test with it and use it.

    The EN guidence is to use the power tap even when you have a computrainer as when you can go outside you will be using the power tap anyway.

    Personally, I know that I will have very few rides outside during the OS, therefore for the 20 weeks of the OS and test and use the computrainer as my powermeter.  As soon as the OS is over I re-test outside with the power tap and use that for the entire season as that is what I will race with.

     

  • wieczynskiwieczynski
    Steve: Ditto what Matt said. One other thing is that both the computrainer and the powertap need to be calibrated. I always calibrate the compu-trainer, but I only calibrate the powertap about once a week when I'm using both. I would recommend that you recallibrate the powertap to see if this solves the problem. I do tend to use the CT instead of the PT during the OS too. My CT is within about 4 watts of my PT.
  • gilliattgilliatt

    mine is pretty close some days, recently the computrainer has been 10 percent on the high side.  I did put my trainer tire on for the year, I tried something (something old) today and rode it in general exercise mode, it was a lot like riding a fluid trainer being as I'm not doing anything structured it mixed it up a little.

  • Ironman281Ironman281
    My PT just got back from being repaired so I just use the CT. Like Matt, I just get my ftp numbers and train with the CT and those numbers. They are always constant and i know what marks I need to hit by power and HR. I must be doing something right because each time i leave the cave, I feel like puking.
  • CNIDogCNIDog
    Echo the above wrt jut using the CT watts until getting back outside and re-testing FTP on the road. I drove myself nuts trying to reconcile the two for awhile before just going with the CT numbers. In being Type A and trying to get the two to match I did realize that the better I warmed up the tire before setting the RR calibration the closer the two numbers were and remained during the workout. I now pay a little more attention to warming the tire up and shooting for a similar RR before starting the workout not only to minimize the difference between CT and PT but more importantly so that I have more consistency across rides.
  • gilliattgilliatt

     Computrainer has updated some of their guidance on how to calibrate, I bought mine in 2005 and found this manual and using the conti indoor tire to both be good things

    http://www.computrainer.com/html/manuals/CTSA2007.pdf 

    page 23 has some good guidance on it that I hadn't seen before.  Is anyone else using an indoor tire?

  • cwhytecwhyte
    Posted By Geoff Wieczynski on 21 Nov 2009 10:52 PM

    Steve: Ditto what Matt said. One other thing is that both the computrainer and the powertap need to be calibrated. I always calibrate the compu-trainer, but I only calibrate the powertap about once a week when I'm using both. I would recommend that you recallibrate the powertap to see if this solves the problem. I do tend to use the CT instead of the PT during the OS too. My CT is within about 4 watts of my PT.



    Geoff,

    I'm curious, how are you recalibrating your PT? You can't calibrate a PT. Do you mean "zero the torque"?

    Thanks, Chris

  • wieczynskiwieczynski

    Chris:  First, great race in AZ.  And you are right.  My terms are sloppy.  I read the manual a while back and yup that is what I meant.

  • Kevin WalterKevin Walter

    FWIW, I noticed exactly the same thing last year.  The computrainer always read 20 watts or so higher than the PowerTap. Even after zeroing the hub torque on the PT and calibrating the CT. I now have an SRM built into my new bike (moved from 650cc wheels to 700cc so old PT not compatible) and am pleased that it reads within 1-2 watts of the CT every workout. Not that its really that critical, after all its the same weak engine no matter what the numbers say, but being able to skip the fudge factor comparing indoor to outdoor watts is simpler.

    That being said, I think the SRM price was ridiculous. Now that Quarq has a compact crank option, I would consider that strongly (same guts and mechanism as an SRM at 1/3 price) for those in the power meter market.

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