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170/172.5/175 crank arms

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170/172.5/175 crank arms

Old 07-31-14, 12:50 PM
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Fun discussion!
So to get my seatpost to be closer to the minimum insert line without using a Brooks, I simply increase the crank length! Cool! I can now ride a smaller frame! I risk pedal rash on corners though.

I was wondering why my left thigh was experiencing a little pain after commuting with 175's all week and then taking the classic out for a ride with 170's on the weekend! Could this be why I like the Pinarello more than the Colnago because one is 172.5 and the other is 170?

Lots of questions and food for thought!

Damn, shouldnt' have sold those 165 NR cranks!
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Old 07-31-14, 01:29 PM
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Originally Posted by reddog3

I tried searching it again, can't find it. But came across this interesting article- Crank Length: Coming Full Circle - Cycling Utah | Cycling Utah

Take away (for me)

"So switching from 175 to 172.5 mm would likely have little measurable or even undetectable benefit. The main point is that you would be safe switching to shorter cranks for aerodynamic reasons, as proposed by Cobb, without fear of decreasing efficiency. In fact, research implies your efficiency would increase somewhat.”

Seems to be based on the linear velocity of pedal, which for a given cadence is higher with longer crank.

scott s.
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Old 07-31-14, 03:55 PM
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Originally Posted by scott967
........Seems to be based on the linear velocity of pedal, which for a given cadence is higher with longer crank.

scott s.
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And you'll probably have a higher cadence with a shorter crank, at least until you go "too short" for your leg length.
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Old 07-31-14, 08:24 PM
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@FBinNY, great points, and if hadn't thought of it that way. I do think a lot of it is based on muscle memory, so it makes sense that a crank of a length I'm not used to will feel weird. But of course, I could get used to it.

I'm just amazed at how I can perceive such small changes, if I'm not fooling myself. It ought to be possible to do blind comparisons, though it would be tedious.
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Old 08-01-14, 06:08 PM
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All my bikes came with, and have, 170s. Always worked fine for me. Never saw a need to change them.
Does that make me "average"?
Dang.
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Old 08-08-14, 09:51 AM
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@rootboy - in this case yes, overall, no.

The 91 Pin has 175 cranks and I can tell. The RockHopper has 172.5 and is the standard against which I judge. Granted, gear/inch are never matched between bikes, but after riding the RockHopper home and jumping on the Pin for a cool down ride, I could tell something more than the gearing, tires and bike overall response was different, like my feet were going in a bigger circle!
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Old 08-08-14, 11:25 AM
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bres dad, Years ago I had road bikes with crank arm lengths ranging from 165 mm to 175 mm. When I switched from one to the other I would notice the difference, but then after a short while I adjusted and the difference became unnoticed. All of my road bikes except for one now have 170 mm long crank arms. I took the 175 mm bike out Wednesday and didn't notice any difference what so ever. In fact I didn't even think about the subject. Because I transitioned easily between 170 mm and 175 mm crank arms I spec'd 172.5 mm crank arms for many of my builds.

When I needed a triple equipped distance roadie after the third injury to my left knee I spec'd a 175 mm crank set. I know it has more to do with a placebo effect, but I was able to put thousands of miles on that bike. My current distance bike is another triple equipped roadie with 175 mm crank arms.

Brad
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Old 08-08-14, 02:59 PM
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I'm 6'2" and have been riding 180mm cranks on my bikes since the mid-'90s. I also have one set of 177.5mm and rode those for a couple months and they felt short to me.

I recall an article in the old "Winning" magazine about climbs on one of the classics. Whoever wrote it borrowed a bike from the 7-Eleven team and made a comment about the cranks. He said he was used to 177.5mm but the 7-Eleven bike had 175mm and he "really missed those extra 2.5mm."

Without adding up the score on who can sense things, it seems that those accustomed to riding shorter cranks notice it less than those in the longer crowd.

Or maybe they just don't care.
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