Powermatch with assioma uno and kickr snap power slipping in vo2 max efforts

trainer
power-meter

#1

I am wondering if I am doing anything wrong or if there is a fault in my set up. I’ve a Assioma uno (left only) power meter and a kickr snap. I use auto power match.
When I do certain efforts and intervals ie vo2 max such as spenser (3 min 120% ftp at 100rpm) I find that my power slips and erg then can’t keep me at the correct target power. I try to increase my power by pedalling harder but instead increase cadence and my power slips further. As a result I’m often 15 or 20 watts under at the end of interval. Does this make sense?
It seems to be something to do with the inertia of the flywheel overtaking my power, or at least this is my best guess. I don’t know how to resolve it. Tonight in Spenser I switched back to my kickr snap as the power meter after the first interval and it tracked well and I could hold the power perfectly.
Has anyone encountered this or knows what is happening and how best to sort it?
Thanks


#2

I think the issue here is coming from using PowerMatch. In this situation, you’re using a single-sided power meter at the pedal (closest to the input of power) and a wheel-on trainer. Crank and pedal based power meters are more sensitive to small changes in force and can be more erratic than a hub power meter or trainer. Because these small fluctuations are being doubled (coming from the left side only), the margin of error increases.

This highly variable data is what PowerMatch depends on to control your trainer, and due to the erratic power readings from the pedal and the lag between that measurement and the application of resistance at the trainer, an ongoing “lagging offset” occurs. Pedaling quicker makes it worse because the trainer’s own ERG mode tries to lighten the resistance applied, while the power readings continue to change.

My recommendation for your setup (as long as there’s not a huge difference in power measurement between your trainer and pedals) would be to disable PowerMatch in your trainer’s pairing settings in the device screen. You’ll still keep both devices paired, but the trainer will handle the ERG control on its own (and probably lock you into the intervals a bit better) while the recorded and displayed data will come directly from the Assioma pedals - meaning you can still use these numbers to compare to your outdoor efforts.

I hope this helps!


#3

Thanks. That makes total sense.