Longer crank arms

[Bentley]

So I'm in a cycling program and I have been using a bike I picked up recently to do the "training". I've noticed my spinning has been affected and I decided to check the crank arm length, turns out its a 180 (need to get an accurate measurement but it 7+" CTC). My regular crank arm length is 172.5.

My thought is at the top, I have to be 7.5 cm higher than normal and would be 7.5mm lower at the bottom. Bottom line, even if the measurements are off, its affecting my pedal stroke, right?

TIA

Ray

[Ken Robb]

I have ridden 170, 172.5, 175, and 180 cranks. I can't tell 2.5mm difference but I can tell 5mm. difference. I bought a bike with 180 cranks for the first time I used any that long. I noticed a very obvious increase in my ability to muscle up hills in bigger gears and I thought this was a good change. Buy, after a short while my knees started to tell me to go back to 175mm.
I have only had one bike with 170mm. cranks in many years and I could turn higher RPM easier with them than with my 175mm. cranks.

If you have the opportunity to try different lengths (especially on the same bike) you may find you have a strong preference for a length other than what you have been riding.

[brockd15]

I have ridden 170, 172.5, 175, and 180 cranks. I can't tell 2.5mm difference but I can tell 5mm. difference. I bought a bike with 180 cranks for the first time I used any that long. I noticed a very obvious increase in my ability to muscle up hills in bigger gears and I thought this was a good change. Buy, after a short while my knees started to tell me to go back to 175mm.
I have only had one bike with 170mm. cranks in many years and I could turn higher RPM easier with them than with my 175mm. cranks.

If you have the opportunity to try different lengths (especially on the same bike) you may find you have a strong preference for a length other than what you have been riding.

Same here, I can't tell a 2.5mm difference but can with 5mm. I'm not much of a spinner and prefer 175mm, have tried 177.5 and 172.5 and couldn't tell much difference from 175mm, but with 170mm I get some knee pain when climbing out of the saddle.

[Bentley]

What I've noticed is my stroke is not smooth and I have a lot of body movement. I set the saddle height so the saddle is the same relative length as my 172.5, but my coach noticed my stroke was off

Thanks

Ray

[carpediemracing]

I have bounced between 170 and 175 a few times in the last 10 years, trying to return to the "faster" 170s and get away from the "slower" 175s. I always keep the saddle-pedal distance the same so the 175s would mean dropping the saddle 5mm. This means my foot comes up 10mm more since I'm referencing the pedal at the bottom of the stroke, not halfway up.

I have very fragile knees and learned quickly that it's extension that hurts me, not the opposite-of-extension.

If I'm too fat then I knee myself in the gut on the upstrokes. It's a pretty sobering thing to have happen.

I'd give a new crank length 4-6 months to acclimate, and I'd focus on pedal stroke almost exclusively for the first few weeks. Low resistance, make circles quickly. My pedal stroke is way off for the first few weeks, even with the saddle change.

I've used 170s probably a total of 15-18 years. I've used 175s for about 10. I used 167.5s for maybe 6 years. Currently I'm fastest/best on 175s.

I have really really short legs. 28.5" inseam, give or take.

[Bentley]

You and I have very similar leg length and I don't see you using 180's. This was not a conscious experiment it was an accident because I never thought to check the crank length. I'm a 172.5 guy, all my bikes (except this one) have 172.5

Gonna change them

Thanks

[echelon_john]

What are the 180s? (In case you want to move them along to someone...)

; )

[donevwil]

What are the 180s? (In case you want to move them along to someone...)

; )

Damn you John !! We 180'ers need to stick together. No jumping the opportunity.:banana::beer:

[Bentley]

The cranks are Ultegra 9 SPD. Had not even gotten to thinking about what to do with them

😀

[redir]

Yes it you are correct to note that it affects your pedal stroke. I have 180's and 177.5 and at 6'4" with long monkey legs they work for me well. Don't forget that you actually have to lower your saddle with longer cranks.

[Bentley]

So I set the saddle at the same relative height to my bike that I was fitted to so it should be the right height at the bottom.

Means it is likely too low when the pedal is at the top, right?

Ray

[echelon_john]

Yes, the extension at the bottom should be the same (or very close) and you'd feel the difference when your knees hit your chest.

[redir]

So I set the saddle at the same relative height to my bike that I was fitted to so it should be the right height at the bottom.

Means it is likely too low when the pedal is at the top, right?

Ray

The bottom measurement is the one that counts. You can bend the leg to account for the difference at the top, and that's kind of the point in getting longer cranks for taller people, but you cannot physically extend the leg longer than necessary at the bottom. So that's what your baseline is.

[donevwil]

The cranks are Ultegra 9 SPD. Had not even gotten to thinking about what to do with them

😀

To my knowledge (I'm a Campy guy) Ultegra cranks never came in 180mm, I believe 175mm are the longest.

[commonguy001]

To my knowledge (I'm a Campy guy) Ultegra cranks never came in 180mm, I believe 175mm are the longest.

I believe you're correct. I've never seen a 180mm Ultegra. They should be stamped with the length down by the pedal threads if you want to make sure.



I'll say - I've ridden 175mm cranks mostly over the last 15-20 years and was always comfortable on them. Tried 177.5 on my TT bike a dozen or so years ago and always felt like I had a hard time getting on top of them if that makes sense. Went to a 175 and it was fine.

By mistake I ordered 172.5 for a build and decided to stick with them. Well I like them more than the 175 length so any new stuff I get I'll be migrating that way.

[cp43]

So I'm in a cycling program and I have been using a bike I picked up recently to do the "training". I've noticed my spinning has been affected and I decided to check the crank arm length, turns out its a 180 (need to get an accurate measurement but it 7+" CTC). My regular crank arm length is 172.5.

My thought is at the top, I have to be 7.5 cm higher than normal and would be 7.5mm lower at the bottom. Bottom line, even if the measurements are off, its affecting my pedal stroke, right?

TIA

Ray

The length should be stamped on the inboard side of the crank. Like this:

http://guides.wiggle.co.uk/sites/default/files/u126/crank-length-display-image1_0.jpg

I'd check there, it avoids the possibility of measurement error.

Chris