Don't worry about going shorter with the cranks for the purposes of spinning only. It is not "easier" to spin with short cranks. Instead, you are forced to spin more because you are moving in smaller circles, but you may need to exert more power to the pedals. So, it is "easier" to turn longer cranks, because you have more torque. Some big power sprinters and time trialists use long cranks with very large rings (like 56T). You just have more knee action in a larger circle, which can make for fit issues and knee issues if you're using cranks that are too long for your leg biomechanics. For small changes in crank length, IMO it is difficult to notice the ease or difficulty of turning the cranks. For some people, it's difficult to notice the fit differences, too (though 2.5mm longer hurts my knees, personally).




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