Crankarm length?

beans

Just wondering how the ratio of crankarm length to leg length has effected your riding in the past?

Traditional road-bike wisdom dictates

traditionalWisdom wrote:

if your inseam is less than 29 inches, use 165-mm crankarms; 29-32 inches, 170 mm; 33-34 inches, 172.5; and more than 34 inches, 175 mm

which makes my cranks a whopping 10mm too long in total - at 175mm Vs 31inches.

So what are your measurements, and how have changes to crank-arm length effected your comfort in the saddle over time, if at all?

Greyspoke

If your bike is an mtb then don't worry too much about it as cranks are usually longer on mountain bikes - 175mm would be pretty standard

beans

Sorry, meant to say it's a road-bike

short circuit

Easier to mash on longer cranks ... easier to spin on shorter ones.

Moved from a 172.5 to 170 myself with change of bike ... and I notice it especially when I am mashing up a hill and out of lower gears .. its tougher ... but I am able to spin quite fast .. so my speeds when I do have the right gear is higher.

sy

Worth noting that the shorter crank length puts less stress on the knee joint

blorg

Interesting, I have always used 175mm cranks, simply because the first bike I got had them 33.75" inseam, so it seems I am not too far off. Considering 170mm for a new fixed crankset though, simply as they don't come any longer.

RobFowl

Interested in this one as well . I'm 5ft 9 1/2 (1/2's very important !!) and have a 32.5inch inseam. I use 170's at the moment on the road bikes but am thinking of changing to 172.5s on my new one. Are there any links to sizing sites or whats the consensus (have 175's on my MTB but thats standard AFAIK)

bcmf

34" inseam with 170mm cranks.No wonder my seatpost is so high.

beans

Recent hip-pain made me ask - but that could be from increased hours in the saddle. I can see how a small change could make a big difference over time.

I run 170s on my fixed bike too - but it's hard to be objective comparing the two. I can never say if it really feels like more work to spin them, or is it the momentum of the fix? If I ever change to a double or compact, I'd like to try a 170 to see

scottreynolds

RobFowl wrote: »

Interested in this one as well . I'm 5ft 9 1/2 (1/2's very important !!) and have a 32.5inch inseam. I use 170's at the moment on the road bikes but am thinking of changing to 172.5s on my new one. Are there any links to sizing sites or whats tha consensus (have 175's on my MTB but thats standard AFAIK)

Read this a while ago when I was thnking of building a frame -- http://www.peterwhitecycles.com/fitting.htm

So how long should the cranks be? Well, that's a good question. I wish I had a good answer but I don't. It should be obvious that a 5' 2" rider would not want to use the same length crank arms as a 6' 7" rider unless they somehow managed to have the same leg length (highly unlikely). Some research has been done to determine the optimum percentage of leg length to crank length. I doubt that there is an optimum percentage that would apply to all people. One writer in a major magazine article quite a few years ago claimed that after considerable testing with many different riders, 18.5% of the distance from the top of the femur to the floor in bare feet should be the crank length. You can find the top of the femur pretty easily. It's 5" to 6" below your hip bone, and moves rearward when you raise your knee. After reading this I promptly changed from the industry standard 170mm cranks for road bikes to 175mm cranks. There was an immediate improvement in power and endurance. I began using this formula when recommending cranks to my customers. So far, I haven't gotten any complaints. But of course that doesn't mean my customers wouldn't be as happy or happier with some other length. And I must admit that I have never tried still longer cranks than 175mm for enough time to tell if I would be even happier with them.

Chips Lovell

Pantani, who was 5ft 7in, rode 180mm cranks.

scottreynolds

el tonto wrote: »

Pantani, who was 5ft 7in, rode 180mm cranks.

And he looked like this while riding - :eek:

WicklowRacer

el tonto wrote: »

Pantani, who was 5ft 7in, rode 180mm cranks.

He could've ridden a chopper and would still have won, juice he did.

rottenhat

blorg wrote: »

Interesting, I have always used 175mm cranks, simply because the first bike I got had them 33.75" inseam, so it seems I am not too far off. Considering 170mm for a new fixed crankset though, simply as they don't come any longer.

Not so...you should be able to get a TA Alize track crank in 172.5mm or 175mm if you look around.

bcmf

el tonto wrote: »

Pantani, who was 5ft 7in, rode 180mm cranks.

Yeah but he was as mad as mad thing.

blorg

rottenhat wrote: »

Not so...you should be able to get a TA Alize track crank in 172.5mm or 175mm if you look around.

Actually turns out it was the discounted crank I was looking at that only goes up to 170, it goes up to 175 non-discounted.

Wez

I'm like 1 or 2 inches off from being the "perfect fit" for my cranks, but I have to say, after changing from 170's + 175's to my final 165's, they are my favourite all round!

They are easier to spin, especially at higer cadence, but they also never strike the tarmac when goin around corners (on my fixie) which I've embarassingly had happen on my new road bike!

165mm's all the way!!

blorg

I think I have 175s on my current fixie(s) and despite road bottom bracket heights don't tend to have cornering problems. I would appreciate the easier spinning with shorter cranks but not the more difficult climbing, I would be using this for cycling up big hills.

bcmf

so longer cranks are better for climbing?

rottenhat

yes - longer lever = greater mechanical advantage, i.e. easier to push a given gear against resistance, be that gravity or wind.

niceonetom

i'm not sure if it's still done, but i think some pros used to use longer (180+) cranks for timetrialing to push a really big ring on the front. so it has it's place outside of climbing too. acceleration would suffer i would say, and you'd want good knees to take the extra stress.