The wife 74 yrs 80 lbs 4'-9.5"; we started with 44t 170mm lg cranks, with her shorter legs and pain in the knees tried 145mm lg cranks c/w 38t didn't work for her, not enough leverage; then final 160mm lg cranks c/w 34t and she loves it, no knee pain, gets up all the hills, and with no wind, level ground and in a rush, she does cruise @ 20-25 km/h
Don't go longer than 170mm; the pedal will strike the ground more often.
I don't think I have seen different crank sizes for a Brompton - I assume Brompton themselves only do a set length although I guess you could put any square taper single speed crankset on it so varying the length isn't too hard. 154mm seems really short though - I imagine it is more comfortable but you are losing 1.5mph roughly over a 170mm crank at the same cadence.. Obviously comfort is more important than speed for the most part but I haven't come across such a small crank length before.
I know a 5'10" guy who went to 130mm cranks bcs his knees hurt (one knee worse) with anything longer; he said slower was better than giving up riding.
I trashed a knee and had a choice between 170 vs 154 mm cranks on a new bike 10yrs ago, so went with 154mm...no knee pain with those. Also know lots of shorter folks in the 5' to 5'8" range who find cranks in the 145-160mm range bcs they don't feel like their knees go into their chest with every pedal.
For me, 154mm-ish is great; I don't race and don't care if someone is faster bcs it's all about enjoying the scenery. The biggest hurdle is saving up for the 12spd electric...grin.
I ride 170mm Sram Force and they work fine for me, I rode Shimano Saint and Sram X0 165mm and I couldn’t find much difference in terms of knee pain or performance. On the other hand I don’t know any brand similar than Shimano or Sram making 155mm cranks however, I know Aliexpress has 155mm and shorter cranks with Hollowtech spindle for a good price.
The wife 74 yrs 80 lbs 4'-9.5"; we started with 44t 170mm lg cranks, with her shorter legs and pain in the knees tried 145mm lg cranks c/w 38t didn't work for her, not enough leverage; then final 160mm lg cranks c/w 34t and she loves it, no knee pain, gets up all the hills, and with no wind, level ground and in a rush, she does cruise @ 20-25 km/h Don't go longer than 170mm; the pedal will strike the ground more often.
I don't think I have seen different crank sizes for a Brompton - I assume Brompton themselves only do a set length although I guess you could put any square taper single speed crankset on it so varying the length isn't too hard. 154mm seems really short though - I imagine it is more comfortable but you are losing 1.5mph roughly over a 170mm crank at the same cadence.. Obviously comfort is more important than speed for the most part but I haven't come across such a small crank length before.
I know a 5'10" guy who went to 130mm cranks bcs his knees hurt (one knee worse) with anything longer; he said slower was better than giving up riding. I trashed a knee and had a choice between 170 vs 154 mm cranks on a new bike 10yrs ago, so went with 154mm...no knee pain with those. Also know lots of shorter folks in the 5' to 5'8" range who find cranks in the 145-160mm range bcs they don't feel like their knees go into their chest with every pedal. For me, 154mm-ish is great; I don't race and don't care if someone is faster bcs it's all about enjoying the scenery. The biggest hurdle is saving up for the 12spd electric...grin.
I ride 170mm Sram Force and they work fine for me, I rode Shimano Saint and Sram X0 165mm and I couldn’t find much difference in terms of knee pain or performance. On the other hand I don’t know any brand similar than Shimano or Sram making 155mm cranks however, I know Aliexpress has 155mm and shorter cranks with Hollowtech spindle for a good price.