Does Length Matter?

A short answer:
Shorter cranks (eg 165 - 172.5 mm) are easier to spin and give a bit better clearance when cornering.
Longer cranks (175 mm or longer) give a bit of a mechanical advantage for generating power but are harder to spin at higher cadences.
Most people use 172.5 or 175 mm, including the majority of pros. Lance uses 172.5. It probably makes minimal difference but there are plenty of people who'll swear that 180 mm or 165 mm are the ONLY choice.

Thanks patch70

I hadn't thought about cornering. This would be something to remember if changing to a longer crank.

There are a few worthwhile articles on this subject on the Web if you do a search. I think you'll find a few posts on this and other forums too.

There is a relationship between crank lengths and your height - or more specifically the length your legs above and below the knee - although there is of course no "perfect" length for a given length of leg. As a masters rider of 178cm height, I ride 170, and changed from 172.5 down to the shorter length. My thinking is that the shorter cranks are better suited to my older body and style of riding (spinning, as opposed to pushing the big gears). If I were younger, and riding fewer hills I'd choose a longer crank.

Just my 2 cents worth.

Quoted post said:

Originally posted by MuzzaB
If I were younger, and riding fewer hills I'd choose a longer crank.

Just my 2 cents worth.

So shorter cranks are better for hill... is that correct?

From 170 to 175 mm is only 0.2 inches, so we're talking about a small differences here. The trend seems to be to longer arms; my 1974 Raleigh in 60 cm size frame came with 165's.

The shorter crank arms will mean you have to push harder to generate the same torque to go up the hill, so I wouldn't say they are an advantage for hills. For standing and grinding up steep hills at low cadence, I'd prefer longer arms.

On an off-the-shelf bike, usually the cranks are sized to match the frame. EG, a 58 or larger frame would come with 175, while a 54 would come with 170s.

If you're happy with the crank length you've got now, why not just get the same on your new crankset? (The length is usually shown on the back of the crank arms).

The usual caveat is that longer cranks are harder on your knees since the angle your knee makes will be more severe - this is the subject of some debate too but it's worth considering if you're concerned about knee longevity.

Quoted post said:

Originally posted by Dominic Sansom
Thanks patch70

I hadn't thought about cornering. This would be something to remember if changing to a longer crank.

Inside pedal up!! Everything else is just details.

Quoted post said:

Originally posted by DiabloScott
The usual caveat is that longer cranks are harder on your knees since the angle your knee makes will be more severe - this is the subject of some debate too but it's worth considering if you're concerned about knee longevity.

Your leg length is a consideration here too though. I'm 6'4.5" (6'4" in bicycle talk and 6'5" in basketball talk) and I typically use use 180mm cranks. I think that I spin these cranks as easily as a cyclist of average leg length spins 175s. JMHO.

Quoted post said:

Originally posted by boudreaux
Inside pedal up!!

Can't always do this in a race...