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Power reading difference: Quarq vs PT
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 2010-11-05 7:30 PM |
Elite  4235    Spring, TX |  Subject: Power reading difference: Quarq vs PTAnyone have experience switching between a Quarq and PowerTap and how the power readings differ? I know that there's a difference reading power at the crank versus the rear hub due to the drive train losses, but I'm wondering if anyone knows what the range is. I'm thinking I heard 5-10W higher on the crank based PMs. I accidentally came home from the LBS with a borrowed quarq on my bike and have a race on Sunday. Chances are I've already screwed myself but I don't want it to mess up my pacing. I was thinking about doing a quick test on the trainer, but I'm having difficulties getting two different Ant+ computers reading two separate PMs. Nothing new on race day folks... (Jorge, if you read this, I'll be waiting for the lecture later!) |
| 2010-11-05 7:44 PM in reply to: #3197960 |
Master 1728  portland, or | Subject: RE: Power reading difference: Quarq vs PT AndrewMT - 2010-11-05 4:30 PM Anyone have experience switching between a Quarq and PowerTap and how the power readings differ? I know that there's a difference reading power at the crank versus the rear hub due to the drive train losses, but I'm wondering if anyone knows what the range is. I'm thinking I heard 5-10W higher on the crank based PMs. I accidentally came home from the LBS with a borrowed quarq on my bike and have a race on Sunday. Chances are I've already screwed myself but I don't want it to mess up my pacing. I was thinking about doing a quick test on the trainer, but I'm having difficulties getting two different Ant+ computers reading two separate PMs. Nothing new on race day folks... (Jorge, if you read this, I'll be waiting for the lecture later!) KathyG has done comparisons between Quarq and PT and the difference was "significant". I don't recall how much, and I think she's a bit preoccupied with IMF tomorrow. If you've got time to kill you could try searching through her blog. I've been trialing a Quarq for the past few weeks and normally use an SRM. I'm seeing an alarming difference in my peak power numbers (Quarq being higher). To the point that I shipped the quarq back today for factory re-calibration. Personally I would not trust using a quarq for pacing based on values determined from a PT without some test threshold efforts under my belt. Apparently you still have the PT, correct? That would be my choice for the race. Good luck! scott |
| 2010-11-05 7:52 PM in reply to: #3197969 |
Elite 4235 Spring, TX | Subject: RE: Power reading difference: Quarq vs PT yaqui - 2010-11-05 7:44 PM AndrewMT - 2010-11-05 4:30 PM Anyone have experience switching between a Quarq and PowerTap and how the power readings differ? KathyG has done comparisons between Quarq and PT and the difference was "significant". I don't recall how much, and I think she's a bit preoccupied with IMF tomorrow. If you've got time to kill you could try searching through her blog. I've been trialing a Quarq for the past few weeks and normally use an SRM. I'm seeing an alarming difference in my peak power numbers (Quarq being higher). To the point that I shipped the quarq back today for factory re-calibration. Personally I would not trust using a quarq for pacing based on values determined from a PT without some test threshold efforts under my belt. Apparently you still have the PT, correct? That would be my choice for the race. Good luck! scottI know that there's a difference reading power at the crank versus the rear hub due to the drive train losses, but I'm wondering if anyone knows what the range is. I'm thinking I heard 5-10W higher on the crank based PMs. I accidentally came home from the LBS with a borrowed quarq on my bike and have a race on Sunday. Chances are I've already screwed myself but I don't want it to mess up my pacing. I was thinking about doing a quick test on the trainer, but I'm having difficulties getting two different Ant+ computers reading two separate PMs. Nothing new on race day folks... (Jorge, if you read this, I'll be waiting for the lecture later!) That's probably the smart move. You say you saw a large variance in the peak numbers, but how about at a steady effort? Say around 80% of FTP? |
| 2010-11-05 8:50 PM in reply to: #3197960 |
Elite 4235 Spring, TX | Subject: RE: Power reading difference: Quarq vs PT I got creative and got two computers working on the two PMs. I only did a quick 10 min test at both race pace and FTP. After calibration, the Quarq was consistently ~10W higher than the PT. It was tough to determine exactly because they were set to average over different periods, but I found them to correlate fairly well. (found a few posts by KathyG on the subject, but nothing detailed. I'll keep looking.) |
| 2010-11-05 9:02 PM in reply to: #3198002 |
Master 5557 , California | Subject: RE: Power reading difference: Quarq vs PT AndrewMT - 2010-11-05 6:50 PM I got creative and got two computers working on the two PMs. I only did a quick 10 min test at both race pace and FTP. After calibration, the Quarq was consistently ~10W higher than the PT. It was tough to determine exactly because they were set to average over different periods, but I found them to correlate fairly well. (found a few posts by KathyG on the subject, but nothing detailed. I'll keep looking.) That sounds about right - I've heard something in the 2-5% range of your FTP but I haven't tested myself on a Quarq. |
| 2010-11-05 11:13 PM in reply to: #3197960 |
Expert 1706 NoVA | Subject: RE: Power reading difference: Quarq vs PT I seem to remember some posts over on ST about this subject and quarq and PT are thought to be "pretty close" and SRM is usually a bit more off from those two....sounds like your 10W difference is close/on the high end of the difference between quarq and PT.... And I wish I "accidentally" came home with a quarq.......... |
| 2010-11-06 12:44 AM in reply to: #3197960 |
| New user 5 | Subject: RE: Power reading difference: Quarq vs PT AndrewMT - 2010-11-05 6:30 PM Anyone have experience switching between a Quarq and PowerTap and how the power readings differ? I know that there's a difference reading power at the crank versus the rear hub due to the drive train losses, but I'm wondering if anyone knows what the range is. I'm thinking I heard 5-10W higher on the crank based PMs. I accidentally came home from the LBS with a borrowed quarq on my bike and have a race on Sunday. Chances are I've already screwed myself but I don't want it to mess up my pacing. I was thinking about doing a quick test on the trainer, but I'm having difficulties getting two different Ant+ computers reading two separate PMs. Nothing new on race day folks... (Jorge, if you read this, I'll be waiting for the lecture later!) If you're using a Garmin computer (Edge 500 or Edge 705) you can tell it to look for a specific power meter by "typing" in the sensor ID. The Quarq's ID is the number on the sticker in the battery compartment (underneath the battery). If you have the Edge 705, you need to go to the "calibrate" screen and then move the joystick "left" "right" "left" in order to get the field to pop up where you can enter the sensor ID. If you're using a Joule or iBike, I'm not sure if or how you tell the computer to look for a specific sensor ID. Feel free to email or call us if you have any other questions during your test drive of the Quarq. Good luck with your race! Mieke Quarq Technology |
| 2010-11-06 7:11 AM in reply to: #3198002 |
Extreme Veteran 5722 | Subject: RE: Power reading difference: Quarq vs PT AndrewMT - 2010-11-05 8:50 PM After calibration, the Quarq was consistently ~10W higher than the PT. Heck, why do those crazy workouts to build your FTP, just buy a Quarq !! But seriously, isn't it normal the Quarq will show higher power since it is measured before loss in the drive train ? Sounds like a lot of loss however. I know my PT is consistently 10w higher than the CT I got this fall and 10w less than the value measured on a Kinetic trainer. |
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