Normally if the temp outside is different than inside by more than 10deg I will do a “recal” on the G500 15-20 min into a ride. I have noted that if I don’t the power numbers seem off for normal hard efforts when i get 30 min into the ride.
So yesterday I did an indoor TT on a computrainer which wold have exerienced a 60deg temp swing from my calibration period to the end of the ride. I don’t know which numbers were closer to being correct, but the Quarq and CT definitely did not agree. I have limited CT time, this was only 3rd time using one, with previous 2x being one year ago at same event where CT ran 13-18w lower than my other quarq. Yesterday the CT avg was 10w higher. The differences were less at the beginning than at the end in readings. The deal was I “calibrated” the quarq about 15 min after coming indoors with bike from being in my vehicle for 3.5hrs(bike was in car for 3.5 hours, i was not, I was at kids BB game). Outdoor temp was ~10F, indoors was ~70F.
Sadly I was hoping to get an updated FTP reading from the 55min event, but the differences in the readings leaves me unable to reconcile which if either was correct. Mine was a Quarq Red whose calibration number is almost always between -520 and -526(outside normal range but very consistent). I also did a slope check last night which was withing 0.47% of previous reading, changed 1 pt, but is 8 pts from factory setting.
Normally if the temp outside is different than inside by more than 10deg I will do a “recal” on the G500 15-20 min into a ride. I have noted that if I don’t the power numbers seem off for normal hard efforts when i get 30 min into the ride.
So yesterday I did an indoor TT on a computrainer which wold have exerienced a 60deg temp swing from my calibration period to the end of the ride. I don’t know which numbers were closer to being correct, but the Quarq and CT definitely did not agree. I have limited CT time, this was only 3rd time using one, with previous 2x being one year ago at same event where CT ran 13-18w lower than my other quarq. Yesterday the CT avg was 10w higher. The differences were less at the beginning than at the end in readings. The deal was I “calibrated” the quarq about 15 min after coming indoors with bike from being in my vehicle for 3.5hrs(bike was in car for 3.5 hours, i was not, I was at kids BB game). Outdoor temp was ~10F, indoors was ~70F.
Sadly I was hoping to get an updated FTP reading from the 55min event, but the differences in the readings leaves me unable to reconcile which if either was correct. Mine was a Quarq Red whose calibration number is almost always between -520 and -526(outside normal range but very consistent). I also did a slope check last night which was withing 0.47% of previous reading, changed 1 pt, but is 8 pts from factory setting.
IME with Computrainer, just ignore the number. Especially over long hard efforts where the tire will heat up a LOT. Use the quarq. Trying to figure out how two separate powermeters swing relative to each other? No way, especially when one is a Computrainer (which is, remember, calculating power largely based off wheel speed, which is going to be way less responsive).
When and how many times did u run the CT calibration? You’d want an initial rolldown at start since bike was newly mounted. Then around 20 minutes in after the tire and CT are warmed up.
I regularly run my quarq equipped bikes on my CT and they read very close as long as the CT is calibrated after warmup and Quarq is zeroed.
CT was very warmed up, we did one roll down, CT had been in use for 22 hours at that point. only time bike not spinning on it would be the 1 min between getting last bike of and next bike on. Folks dont stop 20 min into every hour during a 24hr TTT to do another rolldown. Tire was warmed up on a power beam in another area.(only 14 CTs for 9 teams and our team was one of the warm up in another area teams) The issue i think from quarq perspective is that it was zeroed while its internals were very cold relative to the time it was on the CT.
With your additional details I can see where it might be the Quarq. Though I thought the Red and later models were less temperature sensitive than the early S975 models. But 60° delta has got to be well outside the expected norm.
The 20 minute advice is just based years of CT experience plus 3 years cross use with the S975 and now Elsa. If you have drift all you can do is recalibrate the CT and/or rezero the Quarq.
I’ve never tried warming up a trainer tire before mounting it on the CT and running the rolldown. It still wouldn’t surprise me if there was some drift in this interface on the CT side after the initial calibration. I’ll get off long, multihour rides on the CT for a bathroom break or to open/close a window and the press-on value on a start up rolldown will change just from the short stop.
One other CT issue comes to mind. Blowing a fan directly into the vents on the load generator in an effort to cool it. I’m guessing this TTT was at some type of multirider facility so they would likely know not to use this approach. I’ve seen doing this make the load generator drift.
fans on floor were blowing at riders nothing at the CT units, i had a nice industrial fan blowing at me and they teammates still asked if i needed a pan on the ground as a nice lake formed
i had issues with this quarq initially with drifiting offset which finally settled into it -520 value(my other one is ussually -20) and after expierence with PTs being off if not zeroed after at ambient temps, i noted some similar experience with the quarqs but not quite as bad. It just didn’t sink in yesterday that i was subjecting it to a 60deg diffence from zeroing to actual ride.