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What are the advantages/disadvantages with crank length? I currently run 175mm, but I am looking to change to 172.5mm. I know this is not very significant, but I am just looking to get some opinions/feedback between different crank lengths.
 

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Dented n' Spent
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Taz8 said:
What are the advantages/disadvantages with crank length? I currently run 175mm, but I am looking to change to 172.5mm. I know this is not very significant, but I am just looking to get some opinions/feedback between different crank lengths.
I don' t have extensive experience here. But I can say that my knees are weak fragile things and when I went from 172.5 to 170, I could swear they felt better. Seems like such a trivial difference in length. Maybe I was imagining it but I'm going out of my way to stay with short cranks in the future.
 

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I made the change from 170s to 175s a while back and for me there is no going back. it took a while to learn to spin the 175s properly, but now I am really feeling the benefit of them. Going back to 170's now feels very restrictive, and I just can't get the power down with them as well. Everyone is different though so try and see!!
 

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Old man on a bike
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You get more leverage with the longer crank arm, but usually can spin easier with a shorter crank arm; it's usually finding a balance between the two that work well for you and the bike you're using. Usually you can go a bit longer on your mountain bike vs road bike. Crank length is usually proportional to your leg dimensions. There are no fast and firm rules, though, often it is a matter of experimentation to see what works well for you.
 

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Discussion Starter · #7 ·
Thanks for the info. I think I'll give the 172.5mm a try and see if I notice a difference. I'm 5'8" tall, so I think the slightly shorter crank arm may benefit me a bit. We'll see! Thanks again.
 

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I rode on 172.5s for the first time the other day. I was at an LBS and I took a cyclocross bike for a spin. And spin it did! Just going around the block I could tell a noticeable difference. It wasn't mental either because I didn't know they were shorter until after I got back from the ride and asked the shop guy. I don't know which I would actually prefer though. The thing is, I'm 5'8" as well, but I have really long legs (33" inseam), so you'd think I would favor the 175s I've always ridden on.
 

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Last year I changed out my cranks from 175s to 170s because of an article I read somewhere about how it can help someone with anterior knee pain. It actually has helped quite a bit with alleviating the pain. I raised up my seat height to compensate for the shorter cranks. I do notice a tiny bit less leverage when climbing but feel like my spin is more fluid on the descents and flats. I think that part of why it helps the knees is because the knees don't have to bend at as sharp an angle at the top of the stroke especially with the raised seat height. :thumbsup:
 

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I have ridden 175mm on mtb and 172.5 on road bike for 20+ years. That's what they came with and that's what I'm used to. A few years back I swapped the 175 for 170 due to low bb and annoying pedal strikes. That experiment lasted one ride. The 170's felt like I was spinning a kiddie bike and climbed like crap- not enough leverage. I decided to live with pedal strikes or pay better attention to terrain rather than suffer on the short cranks.

Don't know how 172.5 would feel on mtb. My 29'er is the same wheel size as the road bike, and feels just fine with 175. I'm leery about 175 on road bike though, because pedal strike pedaling around corners could be very bad news.

If I had unlimited funds and time, I'm sure I would experiment with 175 and 172.5 on both 29'er and road bikes just to see how they feel. 170 no way. BTW I'm 5'9" and 30" inseam.
 

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I just switched from 175 to 170 on my 29er. I can't tell much of a difference. The 170 feel like they give me a smoother spin. I use 170 on my road bike too.

I went from 172.5 to 170 on my road bike and felt zero difference.

I'm 5'8" with a 30 inseam.
 

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There are the general principles of 'easier on the knees' and 'easier spinning' for shorter cranks and 'better leverage' for longer cranks. Whatever is true, however, you'll get so many differing ideas about how something feels that the best thing may be to try something out if possible.

Personally, I went from 175 to 170 (32" inseam) and thought it was much more comfortable.
 

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Riders On The Storm
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so it just delivered my new FC-M970 172.5mm and i installed i can't find any difference than before... before i had an 175mm FC-M970 but because of an accident that i had, i messed up my old 175mm and i found in very good price the 172.5mm (Brand new in the official box with BB and the removal tool) and i buy it.
I hope it's ok the diameter i am 1.73cm height.

I would like to believe that i didn't make the wrong choice for buying the 172.5mm!
 

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Have tried 165, 170, 172.5 on fixed gear (mostly on the road); 170 most comfy there, and makes it easier to spin fast on descents than 172.5; I hated 165 as it was very difficult to start from rest on an incline (at traffic lights).

Tried 170, 172.5, 175 on road bike; 172.5 most comfy for me, as easier to spin than 175 and better climbing and acceleration from rest than 170.

Tried 170, 172.5, 175, 178 (briefly), 180 on MTB. (180 came on first bike in early 1980s). 172.5 is more comfy for me, 175 is okay too - just as well as 172.5 MTB cranks are rare. For me, 175 kills spin a bit but not an issue off-road. 170 = not enough leverage, 178 is fine uphill but I cannot spin, 180 was crap everywhere and I couldn't find a seat height which wasn't too high at the top of the stroke or the bottom of the stroke or both; I hated the 180mm cranks the whole time I had them.

I'd be surprised if most people couldn't cope with 2.5mm difference, and many won't/don't notice 5mm. The only way to figure out what's best for you is to try things. NB: Q factor/tread width is also a factor in ability to spin, so it's best to keep that constant when trying different lengths. BTW, Q also affects some people's knees, with some liking narrow and some wide.

YMMV!!!
 

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Have tried 165, 170, 172.5 on fixed gear (mostly on the road); 170 most comfy there, and makes it easier to spin fast on descents.

Tried 170, 172.5, 175 on road bike; 172.5 most comfy for me, as easier to spin than 175 and better climbing and acceleration from rest than 170.

Tried 170, 172.5, 175, 178 (briefly), 180 on MTB. (180 came on first bike in early 1980s). 172.5 is more comfy for me, 175 is okay too - just as well as 172.5 MTB cranks are rare. For me, 175 kills spin a bit but not an issue off-road. 170 = not enough leverage, 178 is fine uphill but I cannot spin, 180 was crap everywhere and I couldn't find a seat height which wasn't too high at the top of the stroke or the bottom of the stroke or both; I hated the 180mm cranks the whole time I had them.

I'd be surprised if most people couldn't cope with 2.5mm difference, and many won't/don't notice 5mm. The only way to figure out what's best for you is to try things. NB: Q factor/tread width is also a factor in ability to spin, so it's best to keep that constant when trying different lengths. BTW, Q also affects some people's knees, with some liking narrow and some wide.

YMMV!!!
+1 much wisdom here. Optimum crank length very subjective, relative to rider leg length and limited at the long extreme by bb height. No substitute for experimentation and experience
 
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