Circling back to crank length

Ha, circling.

A couple months ago we talked about shortening cranks for improved pedaling and shredding: Shorter cranks for my Stumpy EVO?

Since then I’ve been thinking about crank length as is relates to leg length and biomechanics. And then our friend Anne sent in this question:

Hi Lee,

You’ve met me [we’ve been working skills for years]. I’m average height for a female 5’4/5’5, with a 28.5in inseam. I run 175mm cranks and run a small frame. The question is would I benefit by having shorter cranks?

I sometimes get hip pain from taking long strides when I walk. When I take shorter strides with faster RPMs (yes, when I walk) I find that my hip doesn’t hurt. Would the same thing apply to pedaling with shorter cranks (say, 170mm) or would it just make me miserable? What would be the benefits vs the drawbacks? I know DH riders run shorter cranks usually, but that’s mainly for clearance.




Thanks for the great question.


If you have pain — especially in your joints — see a medical expert. If you ignore a structural issue, it will get worse, and the surrounding tissues will compensate in stupid and ultimately painful ways. This I know well.

Optimal crank length

The bike industry does not crank out cranks for every possible rider. They build what they can sell, and they try to sell as few versions as they can. Why? 1) The more they make of a certain model, the less each item costs. 2) The more options they sell, the more time/money gets spent keeping track of them.

Most mountain bikes come with 175mm cranks because that size fits the theoretical average rider. But what if you’re bigger or smaller?

Lennard Zinn is a very smart, very experienced bike fitter, builder and writer. His theory, which I totally buy, is that crank length should be proportional to leg length. When a shorter rider turns longer cranks, her legs are forced through a longer-than-optimal range of motion. Pedaling is likely less efficient, and the chance of injury can be increased.

For general cycling, Lennard uses this formula:

Inseam in millimeters x 0.216

Based on this formula, your optimal crank length is 156mm.

Whoa. Not close to 175mm.

One sure sign of too-long cranks: The rider’s hips rock side to side when pedaling out of the saddle. You see this on kids at the BMX track. I’ve also seen this with you, and you might remember me mentioning shorter cranks. I believe the too-big pedal circle puts extra strain on your hips and lower back.

Benefits of shorter cranks

• Pedaling might be easier, more powerful and less painful.

• Increased ground clearance for shredding.

• You get to buy sweet new cranks.

Drawbacks of shorter cranks

• It might take time to adjust to the new pedaling pattern. I believe you’ll like it right away.

• To get the same pressure at the pedal, you’ll need lower gearing.

Learn more at Shorter cranks for my Stumpy EVO?.

Things you can try

• Ride some 165mm cranks. I’ll bet you’ll like ’em. Shimano XT is a great value and comes in this size. Your local bike shop, Trail Head Cyclery, will dial you right in.

• Lennard can make custom cranks down to 130mm.

Have fun out there. Tell me how it goes!


Know more. Have more fun!

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10 replies
  1. Anne says:

    Thanks for answering my question! 🙂

    I do like the idea of running the cranks without the Straitline de factos smacking the ground or the rocks now, since they’re pretty beefy pedals. I bet this will help my cornering since I won’t be standing with my feet so far apart.

    Lower gearing might be difficult. I run 32/22 with 11-36 cassette. Without converting to 11 speed, I don’t really have the chance of rocking some lower gears. Kinda bummed shimano hasn’t come out with an XT version of their 11 speed yet.

    Other option for cranks are the Race Face Atlas as they rock a 165mm as well.

  2. Wendy Engelberg says:

    On my new Canfield I got super short cranks. I had reconstructive knee surgery and was concerned about hitting the terrain and jamming up my knee. No problem at all with the short cranks. I have very long legs, I love them.

  3. Twebeast says:

    one thing I noticed about shortening cranks is that whilst it gives better ground clearance, it is also effectively reducing your bottom bracket drop. This can reduce your stability in cornering

    It’s worthwhile reducing crank length to fit your body size, but personally I’d choose cornering stability over pedal clearance. As an outcome, I readjusted using offset bushes to drop the bike a little

  4. Anne says:

    So I finally measured my inseam the proper way. It’s somewhere between 29.75 and 30. This makes my ideal crank length 163 to 164, but 165mm is most realistic. I did order a set of Race Face Atlas over Shimano, mainly because of the increase of flexibility and not necessarily tied to 10 or 11 speed.

    Twebeast: Thanks for the cornering thoughts. I’ll keep that in mind. So you know, I’m definitely not doing this for pedal clearance as that’s never been a problem for me. I wouldn’t even consider doing this if it weren’t for the amount of time in pain and as a result, in physical therapy.

    Wendy: Thanks for your thoughts on it. I also had reconstructive knee surgery (not on the side the hip hurts, but still..), so I’m hoping it’ll keep my surgical knee happy too.

    Lee: I’m going to start out with 165mm for a month or so before messing with any gearing. 🙂 It’s going to be hard enough figuring out the new spin pattern before messing with the gears. I’ll keep you posted.

  5. Rich says:

    I purchases a set of XTR cranks on sale, and when they arrived they were 170mm length and I realised I have overlooked the unusual size.
    I’m 6 foot tall with very long femurs for my height, so I assumed these would be too small for me and sold them on eBay for a big loss. I have always run 175mm cranks.

  6. Anne says:

    Two weeks on shorter cranks now. Even did a 16 mile ride. No back pain and no knee pain 🙂

    I have to work a bit harder on them, but because I’m also not whacking my pedals, I don’t have this cringe when pedaling in a technical sections and can pedal through it better and faster.

    Thanks Lee! Really appreciate your help with this!


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