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Crank arm length 170 172.5 175 whats the difference?

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Crank arm length 170 172.5 175 whats the difference?

Old 04-19-08, 05:37 AM
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toneb
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Crank arm length 170 172.5 175 whats the difference?

Crank arm length 170 172.5 175 whats the difference? I might be getting a new bike and the sales rep asked which size I wanted. I told him standard size but is there a reason for different sizes?

I'm 5'9
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Old 04-19-08, 05:41 AM
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I am 5'6 and a 1/2 and have 170's.
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Old 04-19-08, 05:42 AM
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I'm 5'11 and i ride 170s on all my bikes too
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Originally Posted by cc700 View Post
i jam my thumbs up and back into the tubes. this way i can point my fingers straight out in front to split the wind and attain an even more aero profile, and the usual fixed gear - zen - connectedness feeling through the drivetrain is multiplied ten fold because my thumbs become one with the tubing.
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Old 04-19-08, 05:50 AM
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I'm 5'9 and ride 172.5's. I had 170's on the old bike, but got 172.5 with the new bike. The 2.5mm extra in length added a bit of leverage on my pedal stroke and I think my body prefers it. I know that whenever I switched bikes I could feel the difference at first, but then as I rode it would normalize.

I also noticed that with the 172.5's I have less knee issues, which seems odd...Since the longer lever should be putting more stress on the knees...Only think I can think is it alters the angle at which my knee bends through the pedal stroke and it seems to prefer that.

With all that said, I don't think there is a gospel rule as to what crankarm length you should use. It tends to be that shorter rides use shorter crank arms and that taller rides use longer ones, but that doesn't mean that two people of the same proportions will use the same crank arm length...

Are you confused?? I am...
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Old 04-19-08, 06:00 AM
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Longer Crank = effectively more bottom end gearing due to increased leverage.

Shorter Crank = more torque when beginning sprinting. After that the longer crank helps you maintain speed better.

With that said......... The everage rider will feel little or no difference.

So just as with the other posts so far....... There's still not a definate answer.
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Old 04-19-08, 06:00 AM
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2.5
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Old 04-19-08, 06:01 AM
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I'm 6'7" with a 34" pants inseam and ride both 172.5s and 175s.
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Old 04-19-08, 06:04 AM
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i'm 5'9" and ride 172.5 because it's what i have.
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Old 04-19-08, 06:04 AM
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Originally Posted by On Your Right View Post
Longer Crank = effectively more bottom end gearing due to increased leverage.

Shorter Crank = more torque when beginning sprinting. After that the longer crank helps you maintain speed better.

With that said......... The everage rider will feel little or no difference.

So just as with the other posts so far....... There's still not a definate answer.
The part about the average rider not feeling a difference just isn't so.
OP, you are average sized and likely would do best on average length cranks.
I am long legged and much prefer 175's.
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Old 04-19-08, 06:11 AM
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I think the whole thing is miniscule. 2.5mm is literally less than an 8th on an inch.
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Old 04-19-08, 06:12 AM
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Originally Posted by Flak View Post
I think the whole thing is miniscule. 2.5mm is literally less than an 8th on an inch.
Exactly
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Originally Posted by cc700 View Post
i jam my thumbs up and back into the tubes. this way i can point my fingers straight out in front to split the wind and attain an even more aero profile, and the usual fixed gear - zen - connectedness feeling through the drivetrain is multiplied ten fold because my thumbs become one with the tubing.
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Old 04-19-08, 07:08 AM
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I have been told,
Riders inseam of less than 29 inches = 165 mm cranks
Inseam of 29 to 32 inches = 170 mm cranks
Inseam of 32 to 34 inches = 172.5 mm cranks
Inseam of 34 and higher = 175 mm cranks
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Old 04-19-08, 07:17 AM
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When I ordered the compact crank for my Klein the 172.5 size wasn't available but I could immediately get the 175 size. I worried myself to death but decided to take a chance on the 175. Honestly, I can't tell a difference. How much difference can 2.5mm make?

I'm 5'10", by the way, so that's right on the average for American men.
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Old 04-19-08, 07:54 AM
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As previously mentioned it is related to leg and femur length.
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Old 04-19-08, 09:42 AM
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Originally Posted by Ramjm_2000 View Post
As previously mentioned it is related to leg and femur length.
I've read that here multiple times, but does anyone have information for correlating femur length with crank length? In place of the inseam generalization, I'd like to see a general chart where XXcm femur goes with XXX.Xmm crank length.
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Old 04-19-08, 09:48 AM
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eddy merckx ran 175s

no more questions
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Old 04-19-08, 09:51 AM
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I've gone from 180's (mtb) to 165 (track bike) and every size in between. Sometimes on the same day (yes I have a garage full of bikes). And I can never tell a difference.

The science, what little there is, seems to say 'meh' about the whole issue.

So I just go with whatever's stock, unless it's a track bike where 165's are a potential safety requirement.
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Old 04-19-08, 09:51 AM
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While that extra 2.5-5.0mm length gives you additional leverage according to the laws of physics, I found no detectable difference going from 172.5 to 175. Now the lighter carbon frame and compact crank was a different story!
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Old 04-19-08, 10:09 AM
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Originally Posted by nathbdp View Post
eddy merckx ran 175s

no more questions
But what size frame did he ride? Stem length? Handlebar width? Seatpost height? Please tell me, as I want to win the Tour de Franc this year!
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Old 04-19-08, 10:48 AM
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Originally Posted by Retro Grouch View Post
When I ordered the compact crank for my Klein the 172.5 size wasn't available but I could immediately get the 175 size. I worried myself to death but decided to take a chance on the 175. Honestly, I can't tell a difference. How much difference can 2.5mm make?

I'm 5'10", by the way, so that's right on the average for American men.
By virtue of miniscule size differences being available...2.5mm increments is telling about what a difference it makes. It is quite noticable to me and I have ridden most of them.
If you have an average inseam 170-172.5mm is fine.
If you are Shack, likely 180-190 would be better. I have a 35.25 inch inseam and 175's feel perfect to me.
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Old 04-19-08, 10:49 AM
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Originally Posted by urbanknight View Post
But what size frame did he ride? Stem length? Handlebar width? Seatpost height? Please tell me, as I want to win the Tour de Franc this year!
You miss the point. In Eddie's day 175 were considered very long cranks. Eddie is a tall man with long inseam and it makes sense he would prefer longer cranks.
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Old 04-19-08, 10:57 AM
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Originally Posted by On Your Right View Post
Longer Crank = effectively more bottom end gearing due to increased leverage.

Shorter Crank = more torque when beginning sprinting. After that the longer crank helps you maintain speed better.

With that said......... The everage rider will feel little or no difference.

So just as with the other posts so far....... There's still not a definate answer.
I'm not sure what you mean here, but shorter cranks can't provide more torque at any point since torque is equal to pedal force X crank length. You might be able to generate more power (torque X RPMs) with shorter cranks because you can spin them faster, but not more torque unless you're pushing on the pedals harder.

-murray
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Old 04-19-08, 11:17 AM
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Originally Posted by mikeE46 View Post
I have been told,
Riders inseam of less than 29 inches = 165 mm cranks
Inseam of 29 to 32 inches = 170 mm cranks
Inseam of 32 to 34 inches = 172.5 mm cranks
Inseam of 34 and higher = 175 mm cranks
best answer thus far, all it needs are photos of cranks.
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Old 04-19-08, 12:17 PM
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Originally Posted by mikeE46 View Post
I have been told,
Riders inseam of less than 29 inches = 165 mm cranks
Inseam of 29 to 32 inches = 170 mm cranks
Inseam of 32 to 34 inches = 172.5 mm cranks
Inseam of 34 and higher = 175 mm cranks
Not an attack on you Mike, but just on the conventional wisdom you heard.

So we're supposed to believe that a 5mm (less than 1/4") is going to compensate for a 4" difference in inseam? Absurd.

Ride your bike.
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Old 04-19-08, 12:31 PM
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Two similar bikes and both with compacts. One has 172.5 and the other 165's. I find I spin faster with the 165's but even that is not great. Swopped cranks from bike to bike- both do hills and they both climb hills as easy as each other- No matter what crank fitted.

Only difference to me is the mental bit. Smaller cranks spin.
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