Crank length question re Tacx and Assioma

I’ve been using a Neo 2 for my inside training for quite awhile now. My trainer bike is an old cyclocross bike with 170 cranks and my road bike and gravel bike both have 172.5’s. I never really gave it much thought until today when I installed my new Assioma Duo pedals (plan to do the gravel bike hack soon). After updating the firmware, changing to crank length in the Assioma app to 170, and doing a zero offset I install the pedals on my trainer bike.

I decided to do a short workout (Volunteer) to see how the power readings compare. Right off I notice that the pedals are reading 25-30 watts higher. I immediately pause the workout and start trying to figure out what’s up. The only thing I can think to do is to switch the crank length back to the default of 172.5 in the Assioma app. As soon as I do that the power readings were nearly identical. So what’s the deal?

If it matters I was running TR on my phone and it was connected to the Neo 2. The Assiomas were connected to my Wahoo Bolt.

The crank length setting for power pedals will always be overridden by whatever the head unit is set to. iirc you’ll need to use the Elemnt App to check what crank length the Assiomas were set to on the Bolt.

again iirc, 2.5mm cranklengh difference is only ~±3% in power readings… that’s a lot less than 20-30W (unless you’re cranking out massive watts).

Power meter comparisons are best done with a known test protocol, maybe a step test. That makes it much easier to identify any major differences across a number of zones.

Thanks Shane. I’ll give they a go tomorrow morning. I’m pretty sure my wife would kill me if I hopped on the trainer for a third time today.

Btw, been watching several of your videos today. Thanks for all the great info.