Join Date: Mar 2005
Location: Philadelphia, PA
Bikes: Jamis Aurora
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170 = 51.14 pounds @ pedals @ 52 rpm = 08.00 mph. – 291 watts @ pedals
175 = 51.14 pounds @ pedals @ 36 rpm = 11.22 mph. - 425 watts @ pedals!
Is broken. You changed gears in there somewhere. With the same gears, the MPH will be the same at the same crank RPM, no matter how long the cranks are.
Somehow, while changing the crank length, you also doubled (or halved depending how you look at it) your gear ratio. I.E. you went from 48/18 to 48/9.
The only thing crank length affects is input torque (which doesn't affect speed because a bicycle has a fixed transmission, no torque-based slippage) and distance travelled by your foot.
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