Cranck length

Discuss light weight issues concerning road bikes & parts.
Joel
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by Joel

Which is the ideal cranck length for an inside leg of 92cm?

by Weenie


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mrowkoob
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by mrowkoob

Joel wrote:Which is the ideal cranck length for an inside leg of 92cm?


I have 96 cm inseam and use 175 (mtb),177,5 (road) and 180 (road)mm....
I have two different Bioracer readings one says I should use 177.5 and one says 180 mm. I would reccomend you to get measured it´s not only your inseam that counts also the lenght of your femoral bone.

If you want to play it safe get 175 mm.

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Samu Ilonen
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by Samu Ilonen

I have 91cm inceam (185cm tall). All cranks road/TT/CC/mtb are 175mm.

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Cyco
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Joined: Sat Nov 30, 2002 4:49 am

by Cyco

I have 93cm inseam, and 1800 cranks on the MtB, Road and track bikes. Looking for some 182.5s or 185s for the TT bike (I'm currently a set of cranks short).

Also measure your Femur/Tibia ratio the higher the number the longer the crank (male average is 1.1).
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MiNtzNUrMth
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by MiNtzNUrMth

I measure my inseam at 92 and my femur/tibia ratio at 1.225 i am running 172.5's do you guys think i should go larger than 175?

Zac

veldt01
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by veldt01

I would say 175 mm is a safe bet. Furthermore longer cranks in carbon are quite hard to get (only FSA, Stronglight). When Aluminium I guess 177.5 would be a good choice. All depending on the type of rider you are, if you're really fast in sprints don't go larger than 175 since longer cranks don't work.

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mrowkoob
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by mrowkoob

If you want longer carbon cranks you better hurry. Stronglight decided not to make 177.5 and 180 mm availiable (Pulsion) so even if it´s listed many places online and in catalogues, you can´t buy them.
FSA sold very few 177.5 and 180 mm cranksets and have therefore discontinued production of sets longer than 175 mm they wont be coming in those lengths in the future. They have less than 50 cranksets in 177.5 mm in stock and wont be producing more. You can buy them directly from the factory, just write them.

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asphaltdude
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by asphaltdude

177,5 and 180 are merely available. Just stupid! The manufacturers stop making them because they think there's no demand for them but there IS! The only problem is you can't find them at a reasonable price! I'd love to buy 180 mm Ultegra's but Shimano doesn't make them :evil:
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jer
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by jer

Here are a couple of links that discuss crank length. The "Kirby Palm Method" http://www.nettally.com/palmk/crankset.html suggests that i ride 180mm cranks. I have an 84 cm inseam. That sounded long to me but I experimented with it for a couple of months and i found that my power output was increased but my useful rpm range was reduced. i.e. They felt more efficient from about 85-92 rpm but less efficient when pedaling faster than 92rpm or slower than 85rpm. This was better for climbs and time trials because it is easy to stay in that narrow range. However, in mountain bike races, criteriums, and road races I found I was using more rpm range to respond to the constant accelerations and changes in pace. I am now using 175mm which corresponds roughly to the "Gallic Coincidence Factor" http://www.cranklength.info/cranks.htm for my leg length, and I find them to be a good compromise. (I had been using 172.5 for years.)

Neither of these formulas takes into account riding style (spinner or gear masher) which is probably related to your fast-twitch/slow twitch muscle fiber ratio and your aerobic capacity, so they are a good place to start but certainly not the definitive word on crank length. Also, it has already been mentioned but femur length is actually a more important factor than leg length in determining crank length but I think femur length is quite difficult to get an accurate measurement for.

If anyone is interested in the relationship between foot speed and crank length I made a simple spreadsheet that displayed foot speed at different rpm with different length cranks. I can try to post it, but I have never tried to attach an excel file before so I don’t know if it will work.

bobalou
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by bobalou

You might consider Zinn Cycles custom cranks:

http://www.zinncycles.com/cranks.aspx

He's got good info in cranks there also.

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mrowkoob
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by mrowkoob

bobalou wrote:You might consider Zinn Cycles custom cranks:

http://www.zinncycles.com/cranks.aspx

He's got good info in cranks there also.


Wow 220 mm cranks.... Try turning while pedalling with those...

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asphaltdude
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by asphaltdude

According to the X 0.21 formula I (96cm inseam) need 202 mm cranks :shock:

When using the X 0,216 I should have 207 mm :shock:

Actually I ride 175's now........
Whow! That's a pretty damn nice garage door!

Joel
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by Joel

After reading this I'll change to 175mm (inseam 172.5mm)
I'm currently using 172.5mm, with no problems yet, but I think 175 will be more efficient. I like the lower rpm, however, I may not use something bigger than 52/14, so sometimes it's spinning. I think 175 will be a safe bet (not losing to much speed and a bigger power output)

bobalou
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by bobalou

asphaltdude wrote:According to the X 0.21 formula I (96cm inseam) need 202 mm cranks :shock:

When using the X 0,216 I should have 207 mm :shock:

Actually I ride 175's now........


If I were you I'd try some longer cranks. You'd get noticably more power I bet.

by Weenie


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asphaltdude
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by asphaltdude

Placed an ad on a Dutch cycling forum and 10 minutes later I got an email from a guy who wants to sell me a pair of 180 mm D-A's :D
Whow! That's a pretty damn nice garage door!

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