Indoor Bike Training and PowerTap Calibration

Triathlon Forum
1

I’ve done a good bit of indoor training over the past couple months, and have started to notice something a bit strange. Sometimes the power reported seems low by about 15-20 watts, especially on easier efforts. So I unclip, do a manual calibration and it might say 512. I can calibrate it a minute later, and get another value, like 504, then a minute later 509, etc. It sort of jumps around between 504-512. How would this affect the reported power output? Also, do I need to periodically manually calibrate it when on the trainer? I know that out on the road, it’ll supposedly auto-calibrate by coasting, but there’s not a whole lot of coasting done on the trainer.

I’m using a G3 PowerTap hub (default firmware, never updated), and a 310XT for my head unit. Fluid2 trainer.

Thanks

2

A trainer is definitely going to require you do some manual zeroing, since you generally never coast for 5 seconds which kicks off the auto zero. We usually do a coast down after the warm up, but a manual zero is even better.

Something that might help prevent how jumpy it is, is to put a fan on the resistant unit and rear wheel, or use a better ventilated room, or just get a HUGE fan. Heat is what causes the drift, and a lot of heat is generated by the resistance unit right next to the hub.

3

Thanks Jack. You’ve encouraged me to “coast more” in the past. I’ll give the dedicated resistance unit fan a shot, and see if this stabilizes things.