Shorter crank arms?

Hey all,
Been on the bike more than previous year so far and am pretty sure I want shorter crank arms. I have been feeling some pressure at the top of my pedalling movement where my quads meet my knees and after some googling I’ve become aware that my knees have to bend at a pretty acute angle at the top of my “stride”.
So I tried raising my seat and it helps but I think shorter cranks would do me better.
Has anyone else tried this? And is it an expensive upgrade?

The only common crank lengths seem to be 170 and 175 mm. Assuming you have 175 mm now, switching to 170 mm would put your foot 10 mm lower at the top of your pedal stroke. Not a lot, but sometimes small adjustments can have significant impacts.

I’ve never dealt with knee pain, but I have found seat height to make a big difference in how my legs feel. If the seat is a little low, it definitely makes me sore. I suggest you make sure you’ve got the optimum seat height first before you think about changing anything else.

As for cost, in most cases you would likely be best off replacing the whole crankset. Price will depend on what you need, but you would probably be looking at $50 minimum if you bought new online and installed it yourself. I have no idea what you’d pay at a shop, but they may be able to offer something used for a good price.


Thanks man. I measured and I believe they are 175 mm currently. I have to get new tires anyway so I’m going to go ahead and get the shorter cranks. I bought the bike used for super cheap so I don’t mind investing in it!

I definitely noticed what you mean about saddle height too. I am a tall guy (6’2") and have it pretty high for street pedalling. I drop it when I’m on a trail though just to be able to move around easier on my bike.

You can get 165mm from Shimano in a couple of their lines- XT and Zee for sure. SRAM has as short as 155mm in NX.

If you are tall like that, 6’2", I would expect 175mm cranks to be fine.

Note, shorter cranks will also give you less leverage, like going to a higher gear. You may only notice this at the lowest gear on long climbs though.

What size is the bike?


I find the seat does not need to be lowered much for trails as long as your shorts don’t get caught up.

Make sure you do not exceed the minimum mark on the seat post though as you can damage the frame. If you up against that limit you can get a longer seat post.

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I’m 6’-3" and have 170 mm cranks on one bike and 175 mm on the other. I don’t notice a difference at all.

A nice upgrade would be a dropper post so you can adjust seat height on the fly. That way you can have it up all the way when you’re pedaling and can get it out of the way quick when you want to be able to move around. They’re not cheap though and some are not very reliable.


I dealt with some knee pain all last summer. I had to take a month or so off and do some physio. I’m also pretty tall (6’4") with long legs. Longer legs makes it easier for your Q-angle to get out of whack. Bike fit wise the thing that made the biggest difference was adjusting my saddle fore/aft. I made sure that when I was in the power phase of the pedal stroke that my knee was directly lined up over the ball of my foot. I also changed the angle of my cleat a bit on my shoes so my heal was tucked in just a tiny bit more.

I picked up a new bike this year which has a dropper post. The dropper is nice. I’m able to set my seat to a perfect height for climbing and just drop it out of the way on the downhills. My previous bike, without a dropper, I had it set at a bit of a compromise so it wasn’t completely in the way on the downhills.

My knee is still not 100% but I’m able to manage it now. Squats and foam rolling made the biggest difference of everything.


[quote=“Ghost, post:7, topic:5269, full:true”]
I’m 6’-3" and have 170 mm cranks on one bike and 175 mm on the other. I don’t notice a difference at all. [/quote]

I have two bikes with 175mm cranks and one with 170mm. When I get one the one with 170’s it feels noticeably shorter to me. Maybe it’s all in my head since I know they are shorter, but I seem to notice a difference.

If I ever find a decent used 175mm crankset I plan to swap them out and see if I can truely tell a difference.

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Funny. I wasn’t thrilled about the fact my new bike was coming with 170 mm cranks because I thought I would notice the difference. Maybe the bikes are different enough that it hides the crank length difference. I agree that trying different lengths on the same bike would be the only way to know for sure.

I’m 6’3" and therefor went to longer cranks at 180mm. Shimano XT. I’d look elsewhere for knee pain first such as cleat angle and saddle height. Might be worth it to get Cyclesmith to do a proper fitting for you on that bike. It’s a service they offer. Cranksets can get expensive quickly. People who switch to platform pedals often report less knee pain.

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Food for thought for sure…
I use platform pedals and I think I have my seat height ok. I’m definitely going to try adjusting it backwards though. I think that may be the problem.
I lent the bike to my buddy this afternoon to ride cause he seems interested and I’m waiting to get it back. He happened to mention he lost a spoke lol
Can’t wait to look for myself both to move the seat back and to see how bad the wheel might be

You can get 155mm to 180mm from TA Specialites e.g.

For what it’s worth I’m 5’10 and ride 170, 172.5 and 175 and notice absolutely no difference. Even 165s are only 5% shorter than 175s so I would posit that is about the limit of noticeability. Or maybe I am just very adaptable to positioning on the bike? Maybe I don’t ride enough to notice :wink:

Regardless if you want to test your theory you will need substantially shorter cranks. My feeling is that it may have a very small effect on efficiency but nary an effect on your knee pain.

I personally doubt the value of a fitting unless you have exhausted all other minor tweaks. Try out all the free advice you find here and in your googling first, at the very least if you then go to a fitting you can tell the person everything you already did that didn’t work so you won’t waste your money.


I got the bike back last night. I’m sad to say my buddy abused it. The back wheel is way out of true with two spokes pulled out as well as a bent seat post. I’m just going to sell him the bike and put the money towards a new one. I’m pretty excited cause it’s a great excuse to upgrade for me!


Sounds like you shouldn’t lend this guy any of your stuff. Hope he buys it for the price it was worth before he broke it.

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You’re right Adam! I’m still turning it into a win. I bought the bike used for $150 over three years ago and I’m selling it to him for $100. Plus it helps him get into the sport

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