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Crank Length?

Old 05-16-23, 06:17 AM
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Crank Length?

Just wondering what crank length everyone rides. I'm 5'10 with a 30 inch inseam and 46 years old. I'm swapping out my 172.5 to a 165mm to give it a try. I've read that it opens up the hip more and is better for older riders. I've also seen a lot of stuff online about studies that show power loss, if any at all, is minimal. Has anyone else wen to shorter cranks? How did it work out?
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Old 05-16-23, 06:45 AM
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I went from 172.5 to 170. It's what was on the bike when I got it. It's not a perceivable diff, to me anyway.
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Old 05-16-23, 06:56 AM
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6'3" here and a few months ago I changed from the stock 175mm cranks that came with my bike down to 172.5mm. I can feel a slight difference, maybe a placebo, but it feels like I can turn over the cranks a little bit easier.
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Old 05-16-23, 07:19 AM
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Kind of surprised that you found a legitimate source that recommends 165 for your size. It will be interesting to get your impressions after you've used them for awhile. FWIW, I'm 5'8" and use 175 and 172.5 interchangeably, can't tell a difference.
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Old 05-16-23, 08:07 AM
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Originally Posted by shelbyfv
Kind of surprised that you found a legitimate source that recommends 165 for your size. It will be interesting to get your impressions after you've used them for awhile. FWIW, I'm 5'8" and use 175 and 172.5 interchangeably, can't tell a difference.

I watch a lot of videos by Bikefit James and the Australian bike fit guy, I think his name is Neil on youtube. They both seem very credible sources on info I look at others too but both guys say that often times for average sized riders going shorter than the standard 172.5 can be beneficial but not always as we each have our own unique biomechanics. I thought I'd give it a try. I should be swapping out the BB and crankset tomorrow and maybe riding on Saturday.
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Old 05-16-23, 09:19 AM
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Pretty much all my life I've been on cranks of 160 to 165 mm. I'm 71" tall with 34.5" inseam. The few times I've tried longer cranks such as 172.5 or even just 170 mm, I didn't like them. And I gave them several months to win me over, but they didn't. And those attempts where in the last 10 years. 165mm seems to do me just fine.

If you spin a high cadence, you might like the shorter cranks. Or you might not. If you like to mash your way up hills and otherwise tend to ride where 75 rpm is about your max comfortable rpm, then you might not care for them.

Last edited by Iride01; 05-16-23 at 09:23 AM.
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Old 05-16-23, 09:49 AM
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Originally Posted by Iride01

If you spin a high cadence, you might like the shorter cranks. Or you might not. If you like to mash your way up hills and otherwise tend to ride where 75 rpm is about your max comfortable rpm, then you might not care for them.
Cadence and load is more a function of gearing than crank length. Shorter cranks will naturally increase your cadence in a particular gear (pedalling a shorter circumference), but shifting even one gear will more than compensate for the difference.

The only thing to consider with crank length is your preferred range of leg motion. I know of 2 very experienced fitters who both generally favour shorter cranks, especially if you are of average height or less and/or have limited joint flexibility.

One of them published a review of crank length based on various previous studies (some conflicting) and his own fitting experience with hundreds of clients. The bottom line was to go shorter when in any doubt. While there are various potential issues with longer cranks, there are very few with shorter cranks.

My personal experience is that I canít tell any significant difference between 170, 172.5 and 175 mm cranks. Iím 6í tall with relatively long legs.
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Old 05-16-23, 10:36 AM
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Originally Posted by PeteHski
Cadence and load is more a function of gearing than crank length. Shorter cranks will naturally increase your cadence in a particular gear (pedalling a shorter circumference), but shifting even one gear will more than compensate for the difference.

The only thing to consider with crank length is your preferred range of leg motion. I know of 2 very experienced fitters who both generally favour shorter cranks, especially if you are of average height or less and/or have limited joint flexibility.

One of them published a review of crank length based on various previous studies (some conflicting) and his own fitting experience with hundreds of clients. The bottom line was to go shorter when in any doubt. While there are various potential issues with longer cranks, there are very few with shorter cranks.

My personal experience is that I canít tell any significant difference between 170, 172.5 and 175 mm cranks. Iím 6í tall with relatively long legs.
So what length do you use?
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Old 05-16-23, 10:47 AM
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Originally Posted by marathon marke
So what length do you use?
I currently have 1 road bike and 1 mtb both on 175 and 1 road bike on 172.5. It's what they came with and I can't honestly tell any difference. But my inseam is in the right ballpark for that kind of crank length according to this fitter's data review:-

https://bikedynamics.co.uk/FitGuidecranks.htm
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Old 05-16-23, 11:20 AM
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Originally Posted by PeteHski
I currently have 1 road bike and 1 mtb both on 175 and 1 road bike on 172.5. It's what they came with and I can't honestly tell any difference. But my inseam is in the right ballpark for that kind of crank length according to this fitter's data review:-

https://bikedynamics.co.uk/FitGuidecranks.htm
I'm 6'-1", with a 35" inseam. I changed from a 170mm to 175mm crank arms about 40 years ago when I started participating in ultramarathon events. I think the longer arms helped me especially, since I preferred climbing out of the saddle.
I've always heard that any change less than 5mm is probably not worth it or noticeable.
I'm 65 now, and still ride 175mm on both my road and mountain bikes, and even though I had a total hip replacement 10 years ago as a result of a crash, I have no problem turning over the 175 arms.
BTW, I'm not sure I'd put much weight in that article, since I don't believe overall height plays an important factor in correct crank arm length. I think upper AND lower leg lengths might be a very important thing to consider. One thing I've always been curious about is the ratio of upper leg length and lower leg length. If you have a long upper, but short lower (in comparison), that might result in a different saddle height than someone who has a longer lower leg length. That shorter lower will result in a more open hip angle at the top of the stroke, than the cyclist who has longer lowers, yet still be the same at the bottom of the stroke.
Thoughts?
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Old 05-16-23, 11:22 AM
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Originally Posted by PeteHski
Cadence and load is more a function of gearing than crank length. Shorter cranks will naturally increase your cadence in a particular gear (pedalling a shorter circumference), but shifting even one gear will more than compensate for the difference.

The only thing to consider with crank length is your preferred range of leg motion. I know of 2 very experienced fitters who both generally favour shorter cranks, especially if you are of average height or less and/or have limited joint flexibility.

One of them published a review of crank length based on various previous studies (some conflicting) and his own fitting experience with hundreds of clients. The bottom line was to go shorter when in any doubt. While there are various potential issues with longer cranks, there are very few with shorter cranks.

My personal experience is that I can’t tell any significant difference between 170, 172.5 and 175 mm cranks. I’m 6’ tall with relatively long legs.
I've read quote a bit that we lose flexibility/mobility as we age and that reducing the length of the crank is generally a good idea as we get older. I'm not exactly ancient at 46 and have decent flexibility. I've read a lot and watched the bike fit guys videos and they echoed what you said in your post; that there are almost no disadvantages to going down a bit in crank length. I'm not racing or chasing grams so pretty much everything my bike is designed around is comfort and injury prevention. Performance comes second. My bike will go as fast and as far as my mind and body will push it, but not at the risk of injury or pain. That's how I look at it.

The main concern I had was will I lose the ability to climb as well. I live in very hilly area and that would not be good. However, from what I've been able to gather, the research suggests there is a very minimal power loss if any at all.

Last edited by DB77; 05-16-23 at 11:27 AM.
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Old 05-16-23, 11:30 AM
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I'm 69" tall with a 32" inseam. I use 172.5s on my road and gravel bike and 175s on my MTBs. When I bought my newest MTB, it came with 170s. I felt like I was lacking the torque I wanted for low-speed, steep stuff. Replacing the 170s with 175s gave me back the feeling I wanted. I definitely noticed the difference. Switching between bikes, I don't notice a difference between crank lengths. It's more about what each bikes feels like as a whole.
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Old 05-16-23, 11:37 AM
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Originally Posted by marathon marke

BTW, I'm not sure I'd put much weight in that article, since I don't believe overall height plays an important factor in correct crank arm length.

Thoughts?
The article doesnít really suggest height plays an important factor either. I know this guy has a lot of relevant experience and a wide range of client case studies, but feel free to disagree with his conclusions.

My other thought is that if we have no issues then crank length is relatively unimportant. But for those with discomfort or pain it could make all the difference.
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Old 05-16-23, 12:08 PM
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I'm only 5ft 8 so not a direct comparison, but I switched to 165 from 172.5. I'm 57 yrs old and sit at a desk all day. My hips hurt less with the shorter cranks and I would not go back. Remember to adjust your seat higher with shorter cranks.
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Old 05-16-23, 12:18 PM
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77" height

In current use I have...
2 cranks at 170mm
1 crank at 172.5mm
2 cranks at 175mm
1 crank at 180mm

Ends up I dont really care what length I ride and 1cm makes no difference to me.
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Old 05-16-23, 12:24 PM
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5'9" and 32.5" inseam. I generally ride 172.5 but have ridden 170. I don't feel/see a difference.
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Old 05-16-23, 01:13 PM
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Originally Posted by DB77

The main concern I had was will I lose the ability to climb as well. I live in very hilly area and that would not be good. However, from what I've been able to gather, the research suggests there is a very minimal power loss if any at all.
That was my only minor concern too. But as long as you have an adequate range of gears then it doesn't really matter. Effectively a longer crank is like pushing a lower gear i.e. less force required at the pedal, but you have to push it further (larger pedal circumference). Power = Torque x Cadence so it balances out. But if you find yourself out of the saddle in your lowest gear on a very steep hill then longer cranks are a slight advantage in terms of gearing.
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Old 05-16-23, 02:38 PM
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It's your leg length that matters. Leg length is NOT pants inseam, it's floor to firm crotch contact in bare feet. I'm only 5'-6" tall but my leg length is 32-5/8 inches or 83cm. I've used 170, 172.5 and 175mm over the years. Back on 170mm now.
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Old 05-16-23, 03:40 PM
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I am 5'5" and used to use 170mm cranks but switched to 165mm. Not sure about opening up the hips, but it does allow me to run less seat post and has less toe tap
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Old 05-16-23, 04:49 PM
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Originally Posted by MidTNBrad
6'3" here and a few months ago I changed from the stock 175mm cranks that came with my bike down to 172.5mm. I can feel a slight difference, maybe a placebo, but it feels like I can turn over the cranks a little bit easier.
Well, by going from 175 mm cranks to 172.5 mm cranks, you are using an ever so slightly shorter lever arm, and so it should be ever so slightly harder.
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Old 05-16-23, 05:40 PM
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Originally Posted by SoSmellyAir
Well, by going from 175 mm cranks to 172.5 mm cranks, you are using an ever so slightly shorter lever arm, and so it should be ever so slightly harder.
True, but you are also pedalling a slightly smaller circumference. So depending on your leg length and range of motion it could feel slightly easier or harder. But the difference is going to be less than a single gear change anyway, so you probably wouldnít notice. I know I donít.
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Old 05-16-23, 08:12 PM
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5'10 with a 31" inseam here and was having a little bit of knee pain with the 172.5s that come on most bikes my size. Swapping to 170 seems to have alleviated the problem. I was even considering 165 before that, but didn't want to lose too much leverage for climbing. Other than the happier knees though, I really don't notice the difference.
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Old 05-16-23, 09:41 PM
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I share your dimensions and age, a few years ago I had to have surgery on my knee and noticed on my mtb with 175mm cranks there was a noticeable slight pain across the front of the knee, so I tossed on 170, the difference was obvious and the pain went away. With my road bike I had 172.5 and while they didn't cause me pain I found them less comfortable to pedal and also found the 53/39 to be more limiting with my more limited training due to family obligations. So when I built my cross bike I went with 170 and between the 48/34 crank and the shorter length I found it was easily the first bike I grabbed without thinking about it, just sold the road bike after not riding it for the last 2 years. I might experiment with 165 on the next bike but I won't go longer than 170 ,just seems easier to pedal.
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Old 05-16-23, 09:45 PM
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I have 170 on one bike and 172.5 on another. I don't really feel a difference. I am 5'11 and 30" Inseam.
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Old 05-17-23, 05:29 AM
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Neil Stanbury is the name of the Australian bike fitting guy on youtube. His stuff seems legit to me.


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