Crank arm length

[Hurley]

Would it be a big deal to switch from a 172.5 crank arm to a 175? Assuming all of the other dimensions of a bike, gearing, and wheel size stays the same? There's a used bike for sale with a 175 and I’ve always had a 172.5.

Thanks, Ed

[rustychisel]

No, shouldn't think so. Drop saddle 2.5mm to compensate is conventional wisdom.

[kramnnim]

I made that switch and noticed it right away. Felt “wrong” until I switched back. Was riding 15+ hours/week at the time though.

[Mike V]

I rode 170 fro many years. I then tried 172 for about ten years and never felt quite right. I have gone back to 170 and never let better. I didn't think it would be that much of a difference but it was.

[eddief]

My new Roubaix came with 175, but I wanted to replace the crank with ultra compact. I decided on 172.5 cuz I thought if I did not like that crank it would be easier to resell and what difference could a couple of mms make. Well I was really most used to 170 and found that 172.5 felt like I was pedaling a truck instead of a bike. Some more sensitive to crank length than others.

I rode 170 fro many years. I then tried 172 for about ten years and never felt quite right. I have gone back to 170 and never let better. I didn't think it would be that much of a difference but it was.

[quattro]

My new Roubaix came with 175...
eddief, wondering how you like your new Roubaix, is it a 2020 with the ability to lock out the front stem shock? With a 175mm crank it looks like you would be on the 58cm frame. I'm looking at the bike and feel I'm between a 56cm and 58cm, how tall are you? I'm 5'11". If you were only going tp have one bike, could this be it? Appreciate your feedback.

quattro

[quattro]

Forgot to add,I just went from 172.5 cranks to 165, been riding the 165's for 2+ months now, I like them, but I'm undecided if I feel the same power. So, this week I plan to switch back to the 172.5 crank's and see how my ride data compares and how my hips and knees feel. Main reason I switched was I've had a total hip replacement and knee issues in the past, it was suggested the 165's would be a better option mainly for my hips. I'll report back after a few weeks back on the 172.5 cranks.

[jamesdak]

I don't notice the difference and have bikes ranging from 170 to 175. Majority are 172.5. I just adjust the saddle for the 170 and 175 cranks and all seems fine to me.

[charliedid]

Would it be a big deal to switch from a 172.5 crank arm to a 175? Assuming all of the other dimensions of a bike, gearing, and wheel size stays the same? There's a used bike for sale with a 175 and I’ve always had a 172.5.

Thanks, Ed

The correct answer is always maybe. Glad to be of help.:p

[R3awak3n]

As long as I can get the setback I need I really notice no different. I currently have 170mm, 172.5 and 175s and they all ride great to me. But some will notice a diff.

[unterhausen]

If you think there will be a difference, then there will. That is not a lot of length difference. The first time I tried 172.5, I switched back nearly immediately. Thought it felt sluggish. That was a long time ago though. Nowadays I switch between 170 and 175 fairly regularly, and barely notice. The big difference between those cranks is Q factor.

[Bisquik]

What's the theory on liking a shorter crank length? Wouldn't you want to have a 175mm crank that would allow you to generate the most amount of torque without increasing force on the pedal??

[Mark McM]

What's the theory on liking a shorter crank length? Wouldn't you want to have a 175mm crank that would allow you to generate the most amount of torque without increasing force on the pedal??

Yes, for the same pedal force, a longer crank will generate more torque. But you'll also have to rotate the crank (and your leg) through a bigger circle, and flex and extend your leg through a larger distance and range of joint angles. Our muscles don't have the same effectiveness throughout their entire range of motion, so shorter cranks may (accent on may) allow us to keep our legs angles within their range of greatest effectiveness.

Other factors:

Some people's have sensitive knees that don't like generating force when the knee is flexed. Shorter cranks allow the knee to remain straighter.

For time trialists, the shorter range of leg flex with small cranks allow the rider to maintain a lower, more aerodynamic posture on the bike.

For triathletes, reducing hip angle when pedaling may help in the transition between cycling and running.

[Bisquik]

Would that preference have anything to do with rider leg length and age? I assume taller could accommodate 175 better than shorter. Do the young professionals use 175?

[cmg]

went from 172.5 to 170 for about 3 seasons. Never could get use to it. Felt like i was spinning unnecessarily. went back to 172.5. I'm short 5'-6" so everything i read said the 165, 170 would work better for me but it didn't.

[Ken Robb]

I have mostly used 175. I can't feel a difference of 2.5 but I can feel 5mm. I can be happy with 170-175. Never tried 177.5. I bought a bike with 180 and at first I loved the longer arms because I could muscle up hills that required a downshift or two on shorter arms but then I started feeling some discomfort under my patella so I went back to shorter arms and that discomfort went away.