I got lazy, is my power screwed up?

I swap my assioma pedals between two bikes, one has 175mm cranks, the other has 172.5. Most of the time I’m good and use the app to update crank lengths. But last week one of the Android 10 updates messed up my bt connection between my mobile and the pedals for a few days, so I did all my workouts last week on the 175 bike with the pedals set to 172.5.

Nothing felt different, so how diligent should I be about updating lengths? Is it a big deal, or on bikes that are so relatively close does it not matter a lot? Thanks!

Yes your numbers will be off, I did the same once (Vectors) and looked up the factor you had to times by to correct the power numbers.

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Thanks! Back to updating the length then.

Had quick look couldn’t find the difference table I looked up but there is a post on here…

Edit: Found it, I think, messaged you.


Power = Torque over Time
1 W = 1 N⋅m / s

Your power pedals are basically weight scales. That’s where the newtons come from. Your cadence is the angular velocity, so that’s where the 1/s comes from. The variable is the lever arm length, i.e. your crank length.

Because you were running longer cranks, actual torque, and thus actual power, was higher than what was recorded. Multiply your power numbers by 175/172.5 = 1.0144.