Changing Crank Size Feels Weird

I have been riding a 58cm Trek 2100 for 10 years and always felt like it was to large. I always felt to stretched out. I’m 5’ 10". So I recently got a new 56cm Trek Emonda ALR. The fit is so much better and I love. The only weird thing is I feel like i’m peddling in tiny little circles. I was used to a 175mm crank length and still ride that on my trainer bike. And the new bike as 172.5mm crank length.

Anyone else notice a huge difference when changing crank length? I’m going to keep riding and see how it feels. But seriously thinking about going to a 175mm crank length since that is what I’m used to, and what I have on my trainer bike. Any thoughts?

Swapped from a 172.5 mm to a 165 mm and was so much more comfortable in the drops. Previously couldnt hold the low position for more than a minute. Felt like my knees were constantly hitting my chest when pedalling.

Im a smaller rider at 5’ 5".

Currently riding a 160mm crank from the previous 165mm and the only noticeable difference is that its much easier to spin (completely personal opinion).

The 1 advantage I would say is that I can go lower for longer since I swapped to a smaller crank. Definitely would not want to ride anything longer now.


I’m 5’5" too (really nice to see other shorties on here), and I flipped from 170 to 165 about 2 years ago. Loved it - smoother pedalling circle, faster cadence, more space around my torso. As the saddle came up 5mm, I could also get a bigger saddle to bar drop.
Then, about a year ago, I bought a new bike that came with 170s fitted (Canyon Ultimate).
It was like an instant leap in FTP. Huge power that just seemed to come from nowhere. Genuinely felt like superman.
So, I’m now back on 170s all round, and I’ve found that my cadence is just as smooth, and I have no trouble keeping my spin up.
I can only assume that 170s just suit my body better, and I needed to spend time on 165s being “constrained” to a smoother, faster cadence to learn what that felt like and allow me to reproduce it autonomously a longer crank.

1 Like

I am actually considering changing down to 165 mm cranks (for better cornering and in the drops efficiency) despite being 6’1. Started off with 175, currently I have 172,5 (didn’t feel the slightest difference when changing, guess the 2,5 mm is too small to notice for a tall guy?). The only problem is that 165 are really hard to come by where I live…

1 Like

I just noticed the difference. After a dozen plus years out of the saddle, I started riding in earnest again about four years ago and on 172.5 cranks on a then-new road bike. Since then, I’ve put countless hours on a 2018 Tri bike with 172.5s and for the past 16 months, more hours on a gravel bike with 172.5s (including something over 800mi in the last 2.5mos). But when I decided to take my 2018 Tri bike off the turbo and put on my “antique” 2002 Tri bike, and adjusting the seat /bars to get close to my gravel bike, I noticed a real difference: the old bike has 180 cranks. I can really feel the difference whenever I’m on the cow horns or in aero. (BTW - I’m 6’1" / 185cm) I will say I do not like the feeling at the top of the (11 to 1 o’clock) but I don’t yet think it’s detrimental, but perhaps time will say otherwise because I do feel compressed at the top of the stroke.

I think for 2.5mm, stick with it unless you’re going for a marginal gain and everything else is optimized.


Yeah probably just give it more time to see if eventually feels more natural.

I have 175mm on my mtb and cx/gravel bike and 172.5mm on my road bike. I spend the vast majority of time on the road bike and when swapping I notice the difference at first, but it’s very minimal. I was worried about the gravel set up, but I don’t think I’ll swap unless it becomes an issue as I put in some seriously long shake out rides.

6’4" and I’ve changed my TT bike from 175mm to 155mm. First ride is tomorrow. Pettit because I anticipate it feeling weird. I’ll let you know how it goes.

I can’t cite the studies at the moment, but isn’t it generally accepted at this point that there is no change in power output between like 145mm and 200mm cranks? I seem to recall a study indicating that someone who is 5’6 riding 170mm cranks is equivalent to someone who is 6’2 riding 135mm cranks, meaning that we have a very constrained set of possible crank sizes for the wide variety of sizes we are.

At 5’10, OP is 1778 millimeters tall, which means they are noticing a crank length difference that is 0.14% of their height. I can believe that the difference is felt, which goes to show how sensitive the human body is.

Related to the aerobic aspects of crank lengths, I even recall one study positing that tending towards shorter cranks was beneficial in virtually all circumstances, particularly because they believed that this would focus the workload of pedaling at the larger muscles closer to the heart and offload the work in the calves.

All of which is to say: a difference between 165mm and 175mm shouldn’t be relevant, and going shorter might offer efficiency gains overall.

I’ll look for studies later.

I recently switched from a 172.5 to 170 because I got an absurd deal on a dura ace crankset. Weird thing my calf feels some strain in it in. Any one know what to do about that?

Did you raise your saddle after installing the cranks? You need to raise it 2.5mm to match the crank change.

Also, you could consider a saddle shift back to adjust for the more rear position of your food in the power phase.

My gravel bike has 175mm cranks. My road bike has 172.5mm cranks. My ultra bike has 165mm cranks. Mostly I select crank size based on which crankset is available or which one is the cheapest. I can’t tell the difference between 165mm and 175mm.

However, if you can and it’s bothering you…and the expense isn’t an issue…I say change them. You can sell the old crankset to mitigate the expense. Even if it’s just an issue in your head, why deal with the psychology when you can just replace the crank? Keep it simple. Support your local bike shop. Everybody wins!

Well, after my first ride on the 155mm cranks, coming from 175s…I noticed nothing. Everything felt exactly the same, but I was sure as hell more aero.

Wouldn’t I want to lower cause the crank is now smaller?

You adjust it based on the bottom of the pedal stroke. Shorter crank is higher so raise the seat, longer crank is lower so lower the seat.


Trippy is correct. Shorter crank needs higher seat.


That may be part of my problem, the seat is to low. I have been slowly raising it up and that seems to have helped. New bike, smaller size, new fit. Its just going to take time for me. But so far loving the smaller size.

I’m guessing this is more a product of the bike/frame and geometry change than the crank length. Especially since you’re only talking about 2.5mm.

1 Like

Bit if a bump…at the recommendation of my fitter I’ve been using 165’s on the TT bike for a while with really amazing results. This week I moved off the 172.5’s to 165’s on a new road bike due to a hip impingement exposed by the new bikes geometry (I think). I don’t know how to explain it clearly but, coming over the top I was using muscles or rather muscles were firing and resisting the natural pedal stroke. Negative watts is a way to look at it. 7.5mm less length (and raising the saddle by close to the same amount) is enough to relieve the hip and am able to come over the top waay easier.

I hope to see the same improvements like I did with the TT bike which are a bit more 5 minute+ power and better economy (lower HR for the same effort). Sprinting doesn’t seem to be negatively affected. Maybe a little slower getting peak torque but, no way to prove and certainly not enough to say positive or negative either way.

Anyways, the point is, some can really benefit from shorter cranks while others not so much. Those who can’t raise the saddle much and hip impinged I seriously recommend seeing a fitter.