birdly

Hi All,
Pretty psyched about a new (to me) bike I picked up over the weekend, but it's fixed/single speed and geared a little low. I'm wondering if anyone can offer- or point me to a simple explanation of how to best figure the balance of crank length and chainring diameter. I found posting about calculating gearing combinations, but nothing that coordinated crank length. I know crank length won't change rpm per speed, but it would change leverage and pedaling effort. Or am I thinking too hard?
Thanks!

bud16415

https://sheldonbrown.com/gain.html

Good read about midway down sheldon explains.

This calculator takes crank length into the mix.

https://home.earthlink.net/~mike.sherman/shift.html

fietsbob

Do you have a cadence preference?

dabac

Most people would pick crank length according to leg length, more or less. Then you'd pick chainring size according to what gear span and ratios, and cadence preferences you have.

HillRider

Lennard Zinn has done a lot of studies on the relationship among crankarm length, rider leg length and the resulting power output. He concluded that, except for personal preference, there was no significant effect.

birdly

Thanks Bud! This is perfect. Sorry I missed it on my own but I appreciate the help. Nice system too. Very senseble.

bud16415

YW
Keep in mind the two common crank lengths you see around are 170 and 175 and that is only a difference of 3/16 of an inch on a crank arm close to 7 inches long. I have never really been able to tell the difference when switching between my two bikes one of each length.

A few months ago my friend came to me with a broken left crank arm (square bore) and was needing the bike for a 30 mile ride in a few hours. I dug thru my junk pile and the only crank arm I had that was close was a 175 and needed a 170. I just put it on and never said a word and asked later how it worked and was told great “can I keep it?” I said sure but its 5 mm longer than the other side. And I was told well it felt great maybe my left leg is 5mm longer. I said maybe it is.

fietsbob

Smaller chainring and smaller cog at same ratio will weigh less ..
but the wear, spread amongst fewer teeth, shortens the wear-life proportionally .


spinning higher RPM shorter cranks have a shorter stroke, F1 vs a tractor motor.

bradtx

birdly, One note about FG crank arms; they're usually on the short side to help prevent pedal strike in turns. If a SS, but not a FG it matters not exxcept for preference.

Brad

davidad

https://www.peterwhitecycles.com/fitting.htm