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Discussion Starter · #1 ·
I have always run 172.5 cranks on road bike. New bike came with 175s as a surprise to me. I have been riding them and MAY have some knee pain (but how many causes of that are there?) Does it make sense to go back to 172.5 and see if this changes things? Has anyone been able to fine tune and/or feel the difference? Related question: should I run same crank length on mtb and road? (Sheldon Brown says no). Does anyone use same crank length, seat height, and seat model on road and mountain? All responses welcome.
 

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I dunno. There's not much difference between 172.5 & 175's. If no one told you, I'd be pretty surprised if you could tell the difference. Between 170 & 177.5 maybe you could tell, but the other diff. is sooo small....
 

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I have found even going from 170 to 175 is detectable however the difference still isn't that much. Didn't experience any problem. Can't imagine that a 2.5mm difference could cause knee probs if seat position has remained pretty much the same. Has your cleat angle changed position ie. toe in / toe out?
Longer cranks will give better leverage at low cadences so could be better for low gear work on a MTB. Shorter cranks on my road bike enabled me to spin easier. I've found that using longer cranks on the road reduced my acceleration ability (pace changing & sprinting) and caused greater fatigue over distance due to the extended range of motion. Even going to 177.5's on my road bike wasn't enough of an advantage on the hills to sacrifice cadence and endurance.
 

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Discussion Starter · #4 ·
Crank length most obvious change

This is a new bike I am on so other factors may have changed. I have tried to make seat height and distance to handle bars the same. I use Speedplay pedals so cleat angle is not a factor, and anyway shoeshave not changed. On my old bike I was running 52 teeth (and actually prefer it) and am now on 53. It seems like it's easier to push the 53 on the same terrain with the longer cranks. I think my candence is lower now.
 

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I run the same crank length (175) and seat height on my MTB and my road bikes. When I switched from 170 to 175 I had to make a concious effort to maintain my cadence for a few weeks, then I was used to the larger motions.
 

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Discussion Starter · #6 ·
How tall are you?

ericm979 said:
I run the same crank length (175) and seat height on my MTB and my road bikes. When I switched from 170 to 175 I had to make a concious effort to maintain my cadence for a few weeks, then I was used to the larger motions.
170 to 175 is a big switch. I did that years ago and noticed a huge difference. I have been on 172.5 road cranks for about a dozen years, though. At 6'1" with a 35 inch inseam are we about the same height?
 

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height doesn't matter...

It's really your upper leg length that matters. If you've got a 35 inch cyclig inseam, you've got plenty of leg length for 175's. I'm only 5'-6.5" tall with a 32-5/8" (83cm) cycling inseam and I have no problem with 175's. I rode 170's for years, moved up to 172.5 for the last 5-6 years and just moved on up to 175mm this year. Figured it was worth trying since I mainly ride the mountains. The change was noticeable, but I've had no problems that I can measure.
 
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