If you are under 5’6” this is an important topic to understand
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Stability and balance suffer when riding cranks too long. More on that topic in my other video here:    • Balance and Stability - GreshFit Bike...  
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Standard mass-produced crank lengths:
175mm
172.5mm
170mm
165mm
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"Shorter" after market lengths I commonly use for riders under 5'6"
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160mm - *note this has cropped up on some recent 11 and 12 speed Shimano and SRAM
155mm
150mm
145mm