At a modest cadence, 170, 175, 180 are all fine. 180 lets the saddle come down
that 5 or 10 mm, Vs, the shorter...
while maintaining the same saddle top to pedal distance.

Standing on the pedals, climbing hills, there is the Leverage to consider..
Plus there is the frame BB height..

so the Low BB on my Brompton has 170 cranks.
Higher BB on The Koga, has the 180..

it also gave the illusion of more saddle setback,
then I bought a different seat post.



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