# Is there really a difference between 170mm and 172.5mm cranks???



## raymond7204

Besides 2.5mm??

How much of a difference/advantage is there because of the 2.5mm difference in length?

For most, is the difference noticeable?

Being on the shorter side, my bikes have normally come with 170mm cranks. I recently got a used bike that has a 175mm crankset. I've been riding it and haven't really noticed too much of a difference. Am I missing something? 


Ray


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## mtbbmet

I noticed that I needed to adjust my saddle height slightly when I swapped cranks. Other than that, no real difference.


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## Dave Hickey

I have a lot of cranksets in the 'ole parts bin. I'm always building/changing parts on bikes.

I rode an entire season with left 170mm and right 172.5mm crank arms on the same bike. I never knew until I found the matching arms in the spare parts box


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## raymond7204

Thanks. I suspected as much. 

I just got a new tri frame and would prefer to use the 172.5mm crank rather than have to buy a new crankset.

For Dave - Can you confirm that right leg is not longer than the left?


and want to use the 172.5m crankset


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## Creakyknees

I went from 172.5 to 175 and my average speed increased by .45mph. 

Of course, it might've been that I went from Campy to C'dale cranks, too. They're hollow, ya know.


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## Kuma601

I noticed it and was unwilling to the change. YMMV...and you'll adapt. I remember Dave posting the 170-172.5 on another thread, I was...


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## SystemShock

I notice the difference, and I doubt I'm much of an outlier... a significant percentage of ppl will notice if their saddle height is 2.5mm off, for example.

But if you're one of the ones who can't notice the difference, that's great– you'll be able ride most any standard crank length and not have to fuss over it. And there'll be a wider selection Craigslist and eBay deals for you to take advantage of. :yesnod:
.


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## Jay Strongbow

I can only speculate but I can notice the difference in my pedal stroke between wearing a thick chamois and a thin one and I'm pretty sure the difference is less than 2.5mm so I'd have to guess I would notice. (yes, I'm the anal type)
It's not a game changer though, I only notice it if I've recently (like the day before) done a long ride with one pair than switch the next ride.......and then it's only something I think about for like a couple miles.

Noticing a change is one thing.....if what you notice is good, bad or indifferent is another and who to heck knows about that. 175 might be a little wrong for you as a shorter person if you go 'by the book' but as long as you're comfortable and feel you ride as well I wouldn't worry about it.


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## fasteddy07

It's about more than saddle hight.
It's the rotational envelope of the spin.
170 - 175 is a MASSIVE (imho) change
I have two road bikes on 180's another regular ride on 175's.
My ride profile is different between the two. 
Longer crank more suited to climbing
Shorter more suited to spinning out, sprinting.

In case you care - my specs as it pertains to cranks -
6'3" ride a 60cm mostly (i have 18 bikes)
Size 13 feet


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## rubbersoul

172.5 is great for me at 6'1"


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## fasteddy07

rubbersoul said:


> 172.5 is great for me at 6'1"


No doubt -
I run 172.5 on the cross bikes and the track bike. Work great.
Not saying you can go wrong - just for me - where you go is different.

From most of what I have read, finding a sizing formula for crank length is the last great mystery of bike fit.


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## Doba

My experience with different crank lengths is very limited. Going from a 175 to a 180 is my only time changing and I noticed a huge difference. I can climb like crazy now. I also went from a standard to a compact at the same time, but it was still noticeable.


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## BikeFixer

rubbersoul said:


> 172.5 is great for me at 6'1"


Perfect example
I'm 5'10" and run 175 so I think in reality it doesn't make as much difference as people think


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## weltyed

i see this come up all the time. i habve no hard scientific evidence, but i swear i can tell a difference.

i have different lengths on my bikes. my fixie has 175, my cannondale has 172.5, my cross has 170, and my steel salsa has 170. im tellin ya, i can feel a difference on pavement, and i think 170 is right for me. the cross and the salsa just feel "right." also, even though it weighs more and i run fatter and knobby tires on my cross, i can go faster without feeling like i am trying harder. it could be fit, but aint crank length part of fit?


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## wanganstyle

sometimes its a ground clearance issue as well, but longer crank = long stroke for torque, slower rpm.s

if you like making torque instead of spinning faster and you have ground clearance, then perhaps a crank length increase would help you.


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## krisdrum

Placebo or not, I can tell the difference. I normally run 170s, but got a pair of 172.5s with a used gruppo I purchased. Rode them on my cross bike for awhile, but always felt like I was struggling a bit with my stroke. Switched the cranks out to 170s and I am definitely more comfortable with the 170s.


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## Creakyknees

I wonder how many of you people that can feel a difference, have exactly the same position - especially saddle height and fore-aft - with both crank lengths.

weltyed - do all your bikes have exactly the same position?


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## rcekstrom

I believe people can tell, because its actually more than 2.5mm the whole pedal stroke has increased by a circumference of 15.7mm the 2.5 is only the Radius = diameter of 5mm when you go from 170 to 172.5

170 to 175 increased 31.4 cir, 5 rad, and 10 D.


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## krisdrum

Creakyknees said:


> I wonder how many of you people that can feel a difference, have exactly the same position - especially saddle height and fore-aft - with both crank lengths.
> 
> weltyed - do all your bikes have exactly the same position?


I did. I simply swapped the 172.5s out for a 170, didn't adjust anything else.


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## rx-79g

If you think different crank arm lengths don't matter, talk to someone with bad knees. They can frequently feel the difference of 2.5mm and may have pain when they didn't before.


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## mangotreat0808

Going through this now, 170 or 172.5. I normally ride a 170, switched to a 172.5, and I definitely feel a big difference. First off, yes, I need to adjust my saddle height, which is lower with a 172.5 crank. Here's the effects on my riding and speed: With the 172.5 (vs 170), I feel a bigger rotation, more effort to spin - that's the con side; the positive side for the 172.5, I seem to be able to climb faster albeit with a more conscious effort like turning a windmill. The 170's make me spin faster, but on the 172.5's I can push a higher gear. So there's a price with the 172.5's - it's not a normal spin, you're more conscious of pedaling, but you do get to climb faster, go faster. I seem to love the 172.5's effect on my speed, but hate the "abnormal" pedaling when I compare it to the fluid and natural pedaling with the 170's. My bike's a 52cm top tube, and my inseam is a 33.


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## satanas

Some people can tell and some people cannot. Those who cannot usually say it doesn't matter. Those who can tell often say the opposite. The only way to know how it affects you is to try it yourself. Whatever opinion anyone has, there will be plenty of others waiting to shout them down. I suggest you do some testing and make up your own mind. FWIW, I tried 165/170/172.5/175/178/180mm cranks on various bikes and found doing so educational.

A couple I know partly dismantled their bikes to ship them home from Europe. One had 170mm cranks and the other 175mm, and they accidentally got swapped between the two bikes. Both have similar leg lengths. Eventually they were switched back after some investigation (and several months). One person couldn't tell the difference and didn't care which cranks they used, while the other instantly felt much more comfortable. Both are high mileage riders, and the more gear-oriented of the two was the one who didn't care what crank length they used.

YMMV - and probably will.

I doubt there is any reliable formula to consistently predict what crank length will suit. IMHO, there's as good a chance of measuring bodies and then knowing whether people will prefer strawberry or chocolate ice cream...


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## wim

rcekstrom said:


> I believe people can tell, because its actually more than 2.5mm the whole pedal stroke has increased by a circumference of 15.7mm the 2.5 is only the Radius = diameter of 5mm when you go from 170 to 172.5
> 
> 170 to 175 increased 31.4 cir, 5 rad, and 10 D.


And if you drop your saddle by 2.5 mm to accomodate the 2.5 mm longer cranks (as many riders do), your _effective_ saddle height at _top_ dead center will be 5 mm less than it was before. Many riders will notice a 5 mm saddle height change at top dead center.


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