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Does the 165mm arm read less?
My understanding is that you need a slightly higher cadence for the same power/speed on a shorter crank, so with a matched cadence, the Stages might read more?
Also as the Quarq assumes the upstroke to approximate the power in the left crank, the fact that this is a longer length might cause some calculation inaccuracy. -
What are the values you are getting?
The 170mm arm should read slightly higher, due to the increased torque.
Bear in mind however that neither is 100% accurate. Most power meters are +/- 2% , so you could have one with -2% accuracy and one with +2 % accuracy.
Also the stages is only measuring power from one leg - a discrepancy of a couple of percent between legs is also common, sometimes considerably more and typically not consistent - it can very between legs at different power levels and fatigue.
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Acliff
danb
@spinnnout
An odd question... would putting a longer crank arm on a PM impact the power reading?
Scenario: strapped a 170mm Stages Left arm to a Quarq Dzero crank with a 165mm arm. The difference between the two readings was substantial. Could this have influenced the Quarqs reading?