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Crank arms lengths
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 Is there any logic between 170 vs 172.5 crank arms being "better"? I ride a 56cm and have a 31.5" inseam, have been under the impression that 172.5 would be the correct length. Now I'm hearing I may have been wrong? Thoughts? Opinions?

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Re: Crank arms lengths [wawaski] [ In reply to ]
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I wouldn't say you're wrong, rather schools of thought have shifted on this topic. I am not a bike fitter. Just a person with a 31.5 inch inseam who's been on various crank lengths. So I can't really advise but can share my experiences.

I've ridden 170 cm cranks on a road bike. Had no thoughts on crank length but had trouble with the gearing (53/39, 12x25) being too tough for me for my level of fitness. Climbing was always a standing and grinding effort, no sit and spin up hills.

I've ridden 172.5 cm cranks with easier gearing (50/34, 11x28) - on both a road and a TT bike. Climbing was easier due to gearing but possibly the longer lever contributed. Eventually I felt off, hip angle too tight at top of pedal stroke (on both bikes), but not readily fixed by raising saddle else bottom of pedal stroke felt a bit too far away (particularly on road bike). The road bike was a custom build (2013); I requested the compact crank but don't know why the fitter had the bike spec'd at 172.5. Later (2015), a different fitter at different shop consulted some reference and said my inseam would be better with a 169 (I think) but 170 was commonly available.

I've ridden 165 cm (50/34, 12x25) on a TT bike. Spinning up hills was easy. I was slighter faster overall because high rpms fit my small engine.

Now I'm on 165 cm (52/36, 11x28) on both my road and TT bikes, and I like the 165 cm fit much better than the 172.5. I was highly concerned about gearing and leverage for climbing; it hasn't been a problem but there's no comparing my fitness now (higher FTP) versus when I had the 170, 53/39 combo (what's FTP?).

My mountain bike has shorter cranks, a tripple, and I have no idea what gearing.

I think some questions for you might be: what kind of bike are you talking about? How are you using it? B/c your prefered crank length might depend on position (road or TT frame), use (eg, road racing, crits, TT's, multisport, commuting), how strong you are and whether you intend to run off the bike.

I don't know how tall you are but am fairly sure a 56 cm frame would be way too big for me. I'm 5'3" and ride a 50 cm road bike and 48 cm TT bike.

Just a cautionary note: if you think you may want to play around with crank lengths, I'd suggest avoiding getting a crank-based power meter as it can turn into any expensive and annoying compatibility issue.

To breathe, to feel, to know I'm alive.
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Re: Crank arms lengths [wawaski] [ In reply to ]
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PS, you're bound to get more input if you consult the main forum. Though be forewarned that crank length discussions can be.... well, triggering for some people.

To breathe, to feel, to know I'm alive.
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Re: Crank arms lengths [wawaski] [ In reply to ]
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I'm on 165s on advice of my fitter (Ian Murray). I love them. At 5'8" 32" inseams they give me the best conversion of speed from power and cadence.

Hillary Trout
San Luis Obispo, CA

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Re: Crank arms lengths [SLOgoing] [ In reply to ]
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Thanks!!!!! Riding a Pinarello rokh, and my Tri bike is an older Guru. Thanks for the info!
S.

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Re: Crank arms lengths [wawaski] [ In reply to ]
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  I'm going to try to see how I can get a "test ride" on crank arms that size, just to see. Ultegra on my Pin and Guru. Considerable (for me anyway) $ for new.
S.

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Re: Crank arms lengths [wawaski] [ In reply to ]
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I have 172.5 and prob 32" inseam, and on recent fit, fitter told me if I were to change that I should change to 165. The thinking behind this is that - at the angles you ride a tri bike - the crank arm length correlates to the range of motion you're continually getting throughout the course of your ride. Longer cranks and the physiology of riding them can cause hip impingement and hip flexor issues on both bike and run. Pros have weighed in that shorter cranks improved bike splits and/or ability to run faster off the bike. If you want to experiment or are having hip issues, then bring it up to your bike fitter. Fitter told me that change could cost <$300.
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Re: Crank arms lengths [wawaski] [ In reply to ]
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I don't know what my inseam is, but it's short... I'm 5'2.5" with short legs. I'm on 165 cranks on my tri bike (with a fairly aggressive position), and 170 on my road bike - only because that's how they came. If I'd had a choice, I'd have swapped in 165s for my road bike too.

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Re: Crank arms lengths [milkmaid1982] [ In reply to ]
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Thanks for the info!!!

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