crank lengths

[mattr]

It makes no odds at all to power or cardiovascular output.

It *can* have an effect on muscles and joints if you are at one end of the range and the cranks are at the other, or if you have poor mobility of joints. (worst case is long cranks, short/immobile legs)

Adding 5mm to your crank needs a 1cm drop in saddle height and means that you effectively have to raise your knee an extra 1cm and close up your hip joint. I don't know about you, but riding with my saddle effectively 1cm too low would a) drive me mad and b) hurt my knees/hips eventually.

If you are tall/long legged/flexible, you can pretty much get away with any length crank.

 

[xerxes]

Re:

Adding 5mm to your crank needs a 1cm drop in saddle height

5mm surely? :?

 

[hamster]

It makes no odds at all to power or cardiovascular output.

Hmm, ish...

Crank length is important to use muscles advantageously. However I agree that 5mm either way will probably have little effect on measurable power. But you can end up over-articulating the knee with longer cranks. I switched to 175's before a week's laden touring and had awful knee pain...this never recurred when I returned to 170. I can't feel the difference between them when riding though.

 

[mattr]

Re: Re:

Adding 5mm to your crank needs a 1cm drop in saddle height

5mm surely? :?

yup, tapping away at work and made a mistake.
5mm drop. The 5mm extra lift on the cranks at tdc gives you a 1cm effective saddle drop. If that makes sense.

 

[Mr.Toad]

Re:

I went from the usual 175mm on my full sus down to 170's and i'm fairly sure I noticed a difference. Pedals seemed easier to spin, but I noticed a loss in torque. It bugged me so I switched back to 175's.

On my single speed I always run 180's to give me a little more leverage on the out of saddle, techy grinding climbs.

On the road it seems like spinning is more important so shorter cranks are probably more appropriate.

 

[hamster]

The torque argument always comes out sometime in the discussion. Indeed longer cranks have the same effect as a smaller chainring - however, the bike has gears and the crank does not turn the wheel directly! You just have to see cheap kids bikes with the wrong length cranks to see how it can go wrong.

Get the right crank length to suit your leg dimensions, then pick gearing to suit.

 

[PurpleFrog]

Can I submit that if legs were not extremely flexible over crank length then we'd have more variation than about 15mm given that bikes have to accomodate adults from, say, 5-2 to 6-4?

And that also the optimum crank length for any rider would vary with position and power output if it was a big deal - seated spinning and standing sprint modes engage the muscles differently.

 

[FINNEY1973]

Just poking my head over the fence from the road bit, hope you don't mind.

Sheldon (as always) discusses the issue here: http://sheldonbrown.com/cranks.html

Interesting reading and it dispelled a few theories I had which were totally wrong. I'm glad I read his article.

 

[Mr.Toad]

Just poking my head over the fence from the road bit, hope you don't mind.

Sheldon (as always) discusses the issue here: http://sheldonbrown.com/cranks.html

Interesting reading and it dispelled a few theories I had which were totally wrong. I'm glad I read his article.

Good read, thanks for posting!

 

[mattr]

http://www.ncbi.nlm.nih.gov/pubmed/21311357