Some say shorter equal faster rotation so more time at high cadence when the assist is in the better zone so range is improved. I know some use a smaller chain ring to achieve this goal, faster cadence/better range.I assume if you shorten cranks you may get less range from battery as your leverage on the pedal is reduced ? It will be nominal with 5mm reduction though.
For a similar Force applied to the pedals (same rider), the difference in Torque from 160mm to 150mm cranks is about 6%. If you sustain a 6% higher cadence because of shorter cranks (60 to 64 rpm) then, at the end of the day impact = 0The only noticeable impact from shorter cranks on an eMTB is more ground clearance. Anything else is largely subjective or "rounding error".
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