Author Topic: moan of the day.part 2  (Read 308 times)

Andre Jute

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Re: moan of the day.part 2
« Reply #15 on: July 16, 2018, 01:03:30 AM »
I was struck by the shortness of the cranks and wondered if that was a fatbike or ebike necessity.

Cranks are scaled to the rider's size. There is no inevitable link to tyre width or electrical assistance. But, years ago when I went into crank length, I heard considerable persuasive opinion that, unless you're really rather short or tall, the common 170mm cranks will suit you fine, an opinion widely supported by the wide steps between crank size: 165 170 175. About that time too someone tried to market 172mm cranks on the assumption that they were somehow (magic?) more efficient; not too many were sold.

In theory, though, longer cranks should give you an easier ride (longer movement at the pedal for the same number of chainring/sprocket teeth turned), though it will probably wreck your knees in short order.

Danneaux

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Re: moan of the day.part 2
« Reply #16 on: July 16, 2018, 04:18:16 AM »
Quote
In theory, though, longer cranks should give you an easier ride (longer movement at the pedal for the same number of chainring/sprocket teeth turned), though it will probably wreck your knees in short order.
This is me, exactly. I cannot tolerate 172 or 175mm cranks; my knees describe too-big circles for my preferred fast-light hummingbird cadence. For me, it is 170 or nothing for all but the very shortest casual rides.

I do have a 1970 u-frame Folder with Thompson (design) bottom bracket ( https://en.wikipedia.org/wiki/Bottom_bracket#Thompson ), 3-sp S-A IGH, 406mm EWD wheels and 150mm(!) cranks. Oddly, I find I cannot spin them as fast as I can my 170s. I'm guessing it is purely due to muscle memory, as I "should" be able to spin the shorter cranks, but 150mm is a pretty big jump shorter than 170mm. One thing I do notice with the 150s is a real lack of torque compared to my regular 170s, understandable given the shorter moment-arm and reduced leverage.

Best,

Dan.

martinf

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Re: moan of the day.part 2
« Reply #17 on: July 16, 2018, 07:39:26 AM »
Cranks are scaled to the rider's size.

Not always. The bicycle designer Mike Burrows uses very short cranks.

I use 150 mm or 155 mm cranks, they solved the knee problems I used to have with the 170 to 175 mm cranks that ought to be more suitable for my height.

As far as I can tell, this change didn't slow me down, I just pedal at a higher cadence than before.

When I ride a borrowed bike, 170 mm cranks feel strange.