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Quarq readings are some 15-20 watts higher than Powertap?

Peter WickPeter Wick
in General Training Discussions

 I haven't gotten a chance to really make a fine comparison between my output on the PT vs. Quarq but I am thinking there's a difference.

My last informal test was a 10 minute session with the PT wheel on my road bike. I was killing myself and managed 285 watts for 10 minutes. This was about a week and a half before my 70.3 in September so I didn't want to go all out for a whole 20 minutes x 2 session. My last test came up with a FTP of 250 watts on the PT. So, I get my bike back from the shop yesterday and I took it out for a ride now that it has my Quarq cranks on it (with a different rear wheel now) and it just seemed to be reading higher power with out any big increase in average speed. Yeah, not much to go on without a real test but I was just wondering.

I'm going to try to do an outdoor 20 min x 2 test tomorrow to find out my starting point for this OS. I'll be very curious to see what happens.

Comments

  • Scott AlexanderScott Alexander
    do you happen to have two computers? I'd compare direct by recording the quarq with one, and use the PT wheel with a 2nd computer. If you can, might be worth it!
  • Chad ScottChad Scott
    Peter, I tested this theory with the PT on the back and the quarq on at the same time. I did 2 FTP test with this and my conclusion was that the Quarq was about 8-10 watts higher. But now that I've ridden the quarq for about 6 months I think it has leveled off and is about the same. I don't have the PT anymore so I can't test it but this is just my opinion based on my effort and numbers.
  • Peter WickPeter Wick
    Good to know someone else may have had a similar experience. I couldn't get the two computer experiment to work when I tried it with my 310XT and 705. Eh, i think I'll live with the new data. ;-)
  • harrastharrast
    My quarq is about 7-8% (around 15-20 watts) higher than my computrainer lab setup. I have observed this many times, so it's not a one-time anomaly. When I ride outside on the quarq I have to adjust my goal numbers up so that I'm not slacking. It's a pain, but I've learned to live with it. I guess the issue could be due to drive train losses, but it really doesn't make any difference. I just use a different set of numbers when I program my quarq/garmin edge 500 workouts and go.
  • Dino SartiDino Sarti
    From what I understand, there will be differences based on watts lost in the power train. Quarq is reading the power at the crank and the Powertop is in the hub at the opposite end of the power train. I have read (on the internet), so take it for what it is worth, this loss can be as much as 5 watts. Add to that that each unit has accuracy of +/- 1-2% and I think you are in the ball park....
  • GMAN 19030GMAN 19030
    I'm with Dino. There's less power loss transfer with the Quarq.
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