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Old 05-19-05, 03:52 PM   #1
infestedguy1
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crank length and speed/power

i know this subject has been beaten to death, so forgive me if i beat it some more. i'm hoping to get some actual time on a track soon (dick lane velodrome which is reopening), and i'm wanting to play a little bit with crank length. i've been running 170mm cranks exclusively on both my bikes, but wanted to try 165mm's, primarily for sprinting. i've been looking at various articles on the biomechanics regarding crank length, saddle height adjustement, changes in gain ratios and all that, but would like to hear from some folks that have (or know someone that has) gone from 170s to 165s and what they've felt in terms of power/speed gained or lost. right now i'm running a 49 -16 and 49 - 15 gear.
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Old 05-19-05, 04:15 PM   #2
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Originally Posted by infestedguy1
i know this subject has been beaten to death, so forgive me if i beat it some more. i'm hoping to get some actual time on a track soon (dick lane velodrome which is reopening), and i'm wanting to play a little bit with crank length. i've been running 170mm cranks exclusively on both my bikes, but wanted to try 165mm's, primarily for sprinting. i've been looking at various articles on the biomechanics regarding crank length, saddle height adjustement, changes in gain ratios and all that, but would like to hear from some folks that have (or know someone that has) gone from 170s to 165s and what they've felt in terms of power/speed gained or lost. right now i'm running a 49 -16 and 49 - 15 gear.

Quickly here we go.longer crank arms are good for bigger chainrings. This is because you have more leverage of the arms to push the gear around.165 or 167.5 are good on the road.

S/F,
CeyA!

Last edited by Ceya; 05-19-05 at 07:11 PM.
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Old 05-19-05, 04:21 PM   #3
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so with that in mind, would 167.5mm cranks offer a good, happy medium between 170s and 165s? would they allow for both torque/power (pushing bigger gears) and spin/speed?
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Old 05-19-05, 07:13 PM   #4
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Yep I have them on my bikes. 167.5 allows you to have a road feel without feeling the road..cliping the corners.

S/F<
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Old 07-03-05, 07:30 PM   #5
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Originally Posted by Ceya
Quickly here we go.longer crank arms are good for bigger chainrings. This is because you have more leverage of the arms to push the gear around.165 or 167.5 are good on the road.

S/F,
CeyA!
I think as long as you hip angle stays optimized and your knee doesn't bend excessively at the top or make a funny angles longer is better up to a point. I can't imagine the hip angle being relatively closed on a steep seat tube angle track frame with a small 165mm crank.

Normaly I get into debates about those who toute "proportional crank length theory", but in those cases we are usually talking about 180mm cranks on people with relatively short legs.

I ride 180mm on a road bike, but then again I had to make forward seat adjustments to keep from losing power compared to my 175s. I also didn't have to worry about dropping pedals on turns eiither like a fixed gear would.

P.S. There was some research done a long time ago that compared different length cranks vs power. Shorter length cranks (110mm) made the most power. Biggest problem with the study was they didn't make any seat adjustments when they went from different length cranks. I forgot the longest crank tested but it was something like a 200+mm. No way is the "optimized" seat position going to be the same when comparing two different length cranks. Even my 175mm and 180mm have two different seat positions on the same bike.

Last edited by 53-11_alltheway; 07-03-05 at 10:49 PM.
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Old 07-05-05, 08:38 AM   #6
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I wouldn't mind going to 170s from 165s. Since buying a road bike I feel like I'm on a Big Wheel with the 165s. I feel like I'd get more from my effort with 170s. Anybody gone this route?
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Old 07-05-05, 05:19 PM   #7
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i actually picked up the 167.5s and really like them. i did have to adjust my seat, but i can tell a difference in spinning ability, although i'm still getting used to them. i had a pretty extensive talk with john at business cycles before i decided on what to go with. he gave me some pretty good advice, ultimately it came down to having a middle of the road crank (spinning and torque), which the 167.5s seem to fit pretty well.
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Old 07-08-05, 06:12 PM   #8
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Newbie question, but aren't you going to ground the pedal on the embankment with 170mm cranks?
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Old 07-08-05, 08:02 PM   #9
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Newbie question, but aren't you going to ground the pedal on the embankment with 170mm cranks?
not necessarily: the track surface is banked and when you hit it at speed and lean, you will still be level so the possibility of pedal striking is pretty negligible from what I have seen. A few other riders at the velo that I have met run 170s as it is a nice balance between spin and power for them. 165mm cranks are good for the spin-up speed and then not pedal-striking on non-banked surfaces, like the street.
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Old 10-26-08, 04:09 AM   #10
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I've changed from 165mm to 170mm cranks specifically for the greater torque it will allow me to produce. I followed this up with some testing at the local university on a velotron (with a correction for the flywheel) and it allowed me to produce another 80watts. That's quite a bit. The lab guy and I predicted it would be between 50-80watts. Its was pretty cool to see the calculation work out. The only down side for the first few weeks at this crank length was my peak cadence on the rollers dropped from 215-220rpm down to 210-215rpm. But now I can spin back up to 222rpm, which I just did this evening.

I think its more of a tradition for track sprinters to ride 165mm cranks. Although I have heard that Shane Kelly rode 170mm.
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Old 10-31-08, 12:55 PM   #11
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I was googling some related info and I came across a website that claims the following procedure for how to determine the proper crank arm length.

This may be of some use to you...


Quote:
For those simply interested in the formula itself, it is simple enough. First, the rider must measure his inseam. It is not recommended that the pants size be used as this may not be accurate enough, an inch one way or the other makes a pretty big difference. Stand barefoot on a hard floor, straight, feet fairly close together, back against a wall, and have an assistant insert a clipboard between your legs. Lift gently, sliding the clipboard as high as it will comfortably go while keeping it firmly against the wall, thereby assuring it isn't tilted. While holding the clipboard this way, measure the distance from the top edge of the clipboard to the floor, in inches. Don't round to the nearest inch; measure as accurately as possible.


L(mm) = 5.48 x I(in)


Now, multiply the inseam measurement (in inches) by 5.48. This provides a good estimate of proper crank length, in millimeters, for general road cycling or racing.
He later states in a related link on the same page that you might want to go no more than 5mm shorter for track-specific cycling but that is just optional.

Last edited by fordfasterr; 10-31-08 at 01:02 PM.
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Old 11-01-08, 12:02 PM   #12
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Formulas like any other rules of thumb should just be considered guidelines. Everybody's body works differently.
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Old 11-01-08, 07:19 PM   #13
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I just got some 175mm dura ace cranks w/ 49 tooth ring, 17t in rear, since it was a good deal on CL. Not sure if I am crazy about them yet.

I had 172.5 Sugino messenger and it seems the only way to compare would be to have 2 or 3 bikes with different length cranks and jump from 1 to another.

I think I would have to ride something stupid short and stupid long to know what is really not working for me.
my 2
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