How does incorrectly specified crank length affect power readings?

I noticed that my Vector 3S's defaulted to 110m rather than 172.5mm crank lengths, and assumed this would significantly affect power readings? If so, would this artificially boost or reduce power?

I'm clutching at straws that this it the reason my FTP has dropped rapidly from ~200 -> ~120 even though I'm faster on the road :-/

Paul.

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lhol over 6 years ago +1

It reduces your power. Power is torque times angelar speed (cadence). Torque is force times arm length (=cranklength). 110 mm instead of 172.5 mm means that your power reading is 110/172.5 = 64% of your…

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0 lhol over 6 years ago

It reduces your power. Power is torque times angelar speed (cadence). Torque is force times arm length (=cranklength). 110 mm instead of 172.5 mm means that your power reading is 110/172.5 = 64% of your actual power.

0 paulspencerwilliams over 6 years ago

And hey presto, a revised forecast FTP of 204 watts. Why, oh why, did I not notice this setting earlier!

0 t_smit over 6 years ago

FYI, the crank length setting is actually managed by the head unit - it will send a crank length setting message to Vector and then that gets stored. So it sounds like your head unit may have had a corrupted crank length setting.