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Old 01-24-12, 09:46 AM   #1
Drummerboy1975
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The cranks too short?

I'm looking at a vintage bike for sale locally and the guys telling me that the crank is too short for him and that's why he's selling. What does he mean? Or do cranks actually come in different sizes?
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Old 01-24-12, 09:56 AM   #2
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They certainly do. Most manufacturers provide adult crankests in a range of 165mm-175mm, in 2.5mm increments. Some manufacturers offer as high as 180mm. Older cranksets, offered in imperial measurements, usually range from 6-1/2" to 7" in 1/4" increments, The size is measured from the center of the spindle hole to the center of the pedal hole and is typically stamped on the back of the arm.

Length of crankarm is usually established based on the length of the thigh, however personal preference and discipline also play big parts. Cyclists who like to spin typically choose a slightly shorter crankarm than what eould be considered normal while low cadence and high torque riders often prefer a slightly longer crankarm. Track cyclists typically favour slightly shorter arms while TT riders and ATB riders generally go slightly longer.

Last edited by T-Mar; 01-24-12 at 10:04 AM. Reason: added 2nd paragraph
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Old 01-24-12, 09:59 AM   #3
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Yes, cranks come in a narrow range of sizes. You are unlikely to find anything shorter than 165 mm or longer than 175 mm. The range of cranks available is much too narrow to allow most riders to chose crank arms proportional to some body measurement, so don't worry about that. In my opinion, shorter is better for all road riding. Serious off-road riding sometimes requires a longer crank arm.

Other forum members will chime in to say longer is better. Don't listen to them.
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Old 01-24-12, 10:01 AM   #4
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Old 01-24-12, 10:08 AM   #5
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Longer is better.

An easy change, sounds like he is rationalizing a new bike.
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Old 01-24-12, 10:10 AM   #6
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He probably means the frames to small....
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Old 01-24-12, 10:23 AM   #7
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He's saying that when he smokes crank, it doesn't do as much for him as it used to. He was probably trying to find out if you have a lab in your basement.
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Old 01-24-12, 10:59 AM   #8
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Ok.

Wouldn't it be easier to just ride on the big gear of your crank and raise ones seats?
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Old 01-24-12, 11:02 AM   #9
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Ok.

Wouldn't it be easier to just ride on the big gear of your crank and raise ones seats?
Not following here. What do you mean?
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Old 01-24-12, 11:18 AM   #10
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Longer is better.
told you! Don't listen to him!

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Originally Posted by Drummerboy1975 View Post
Wouldn't it be easier to just ride on the big gear of your crank and raise ones seats?
No to the first, yes to the second.

No, with shorter crank arms you have (a tiny bit) less leverage, so turning a big gear is (a tiny bit) harder but your feet travel (a tiny bit) slower at a given cadence; so when you speed your feet up to their normal speed you increase your cadence and the bike's speed. In other words, shorter crank arms are better for a higher cadence.

Yes, assuming a standard BB height you will want your seat higher if you use shorter crank arms. Shorten your crank arms by 5 mm, raise your seat by the same amount.
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Old 01-24-12, 11:20 AM   #11
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Ok.

Wouldn't it be easier to just ride on the big gear of your crank and raise ones seats?
Not understanding you. We're not referring to the size of the chainring, it's the length of the crank we're talking about. The crankarm is the thing that attaches the pedal to the bottom bracket. The chainring is the ring of teeth around the bottom bracket that the chain rides on.

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Old 01-24-12, 11:26 AM   #12
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Yes we are all talking about the same thing. But going to thwarting larger chainring changes cadence.
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Old 01-24-12, 11:34 AM   #13
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Thwarting? I dunno man.
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Old 01-24-12, 11:35 AM   #14
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Old 01-24-12, 11:36 AM   #15
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Thwarting? I dunno man.
You just don't get it, man. Probably just over your head.
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Old 01-24-12, 11:59 AM   #16
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2.5mm=0.098425" Not really as big a deal as some would make it out to be.
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Old 01-24-12, 12:02 PM   #17
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Yes we are all talking about the same thing. But going to thwarting larger chainring changes cadence.
What?
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Old 01-24-12, 12:13 PM   #18
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What?
Auto correct on my phone Guys.

Replace the word "thwarting" with "the".
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Old 01-24-12, 12:27 PM   #19
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This might be a good time to hit that button that says "Edit Post." Your call.
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Old 01-24-12, 12:43 PM   #20
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Old 01-24-12, 12:47 PM   #21
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Old 01-24-12, 12:51 PM   #22
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I am thinking that crank length has the most effect to long distance riders who spend hours at a time in the saddle. What may seem as a minor inconvience to those riding for an hour or less becomes a very painful problem to LD riders. A small change of a few cm.s can have a dramatic result.

I have read discussions too concerning the need of LD riders to pedal in concentric circles and fine tuning the crank length can help with this. I am sure some of this can be mental but I am sure some of it may hold a bit of truth to it as well.

To me the guy is justifying the purchase of a new bike. Cranks are easy to swap.
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Old 01-24-12, 01:00 PM   #23
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I am thinking that crank length has the most effect to long distance riders who spend hours at a time in the saddle.
Yes, I think that is true. Riding a century on 170's definitely seems to leave my legs sorer than a century on 165's.

But there's also a matter of getting used to something. I could get used to 170's or longer ones, and I'm sure it would do me no harm; but now that I'm used to 165's and shorter the 170's do make me sore on long rides. Commuting on 170's is not a problem, though.

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To me the guy is justifying the purchase of a new bike. Cranks are easy to swap.
You're probably right about that.

Frankly, Drummerboy, crank arm probably doesn't matter enough to think about it this much. Whatever crank arms are on the bike in question, if you like it, you will not have a problem with the crank arms.
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Old 01-24-12, 01:06 PM   #24
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How often do you type "thwarting " so it trumps "the"on autocorrect?

Or you are typing that bad ...
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Old 01-24-12, 01:08 PM   #25
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2.5mm=0.098425" Not really as big a deal as some would make it out to be.
It can be if you have bad knees. I don't have full range of motion in my R knee, and the difference between 170 & 165 is simply amazing.

Since you raise the seat up 2.5mm, the bottom pedal is 5mm further away.

One can do too much of a "good thing" however. My cadence actually slowed a couple RPM when I went to 160's.
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