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Crank Arm Length

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Crank Arm Length

Old 02-14-20, 03:08 AM
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Originally Posted by HTupolev View Post
Longer cranks give your legs a tiny bit more leverage over the gear, not less.
Yes exactly this. I was going to post a similar observation.

I am 6'2" with 34" inseam and ride a 59-60 frame (center to center non compact) and have always used a 175 crank arm. Most bikes in L or XL will be built with a 175.

Some years ago I borrowed a bike for a weekend ride (was out of town visiting). It was a 57 I think with 172.5 crank arms. I noticed the difference immediately. Less leverage or torque forcing me to always change gears where as with my 175s I could always use the leverage a little bit.
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Old 02-14-20, 03:29 AM
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Welp, after my long post on Feb 8th, I solved my knee twinge issue by switching the entire crankset, including shorter cranks, to the other bike.

The steel bike with 172.5 cranks and round 50/39 chainrings didn't give me any problems. Nor did the 170 cranks with 52/42 Biopace on the carbon fiber bike.

But swapping the Biopace chainrings to the bike with 172.5 caused minor knee problems that persisted for a couple of weeks.

So this week I switched the entire crankset -- 170 cranks and Biopace rings -- to the steel bike. Knee problem gone.

I'm surprised such a minute difference in length made so much difference. But the eccentric, oblong Biopace rings felt surge-y, pulse-y and weird with longer cranks. Paired back with the original shorter cranks they feel right again. The shorter stroke feels more efficient to me.

Now I'm rethinking my cavalier attitude toward crank lengths. I might just switch all my bikes to 170 now. At 62 I've managed to avoid serious knee problems despite many accidents and a family history of deteriorating knees. I'd like to keep 'em healthy as long as possible.
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Old 02-15-20, 09:34 AM
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I am 6'+ and a 35" inseam . Most of my bikes(vintage racers) are either 24" or 25" frames. I only have one bike with 175 cranks , the others are 170 and to be honest I can't tell the difference . My concern when I restored the bike with the 175 cranks was ground clearance and that was not an issue. Joe
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Old 06-22-20, 08:28 PM
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I'm 5'7" with 30" (Levi's) inseam. I bought a Specialized Secteur a couple of years ago with 175 mm cranks. I switched to 165 mm cranks this winter and it seemed to be a great improvement, mostly because it made breathing easier. I'm about 10 lbs overweight, and although I don't think I was actually beating my belly, it does feel more open or something. Hard to say if it was just new toy placebo, but I will probably stick with 165 if I ever have the choice again.
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