Crank arm length?

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2009-09-15 3:38 PM


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Subject: Crank arm length?
I'm just starting to train so that I'm good enough condition to start training.  I don't have enough money for any bike so I'm using my old (non-suspension) MT bike.  Repacked wheel bearings, switched to 1.5 tires, lost the kickstand (save a lb maybe), added alloy clip pedals, and a new seat (still cheaper than even the most junkiest bike I could find- that would only need same amount of work and money).  Did all work myself.

My crank arm length is 170mm.  I'm nearly 6'2".  Should I be looking at longer crank arms?  I know that on my BMX bike (yeah, I'm 40 with a BMX bike) I have 180mm cranks.  Is the same principles involved in the length of MT/Roadish bikes?  The 180mm seam perfect for me on a 20" bike.

Thank you for your advice.

2009-09-15 3:51 PM
in reply to: #2407988

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Sensei
Sin City
Subject: RE: Crank arm length?
I'm not sure if I have an answer for you, but I can tell you what I know.

First, a 180mm MTB crank is probably hard to find cheap.  I just checked Nashbar, and they wanted $270 for their cheapest 180mm.

Second, I would agree that 170mm IS probably too small for you.

Third, road bikes/tri bikes max out at 175mm (stock),  You would have to pay out the arse for a longer crank than that.  This is not surprising, since it is recommended to run a slightly longer crank on you MTB than a road bike.

That being said, I would probably look for a in inexpensive 175mm instead if you are trying to keep the conversion within a budget.  Nashbar sells their brand with a 175mm at 50 bucks or less.  Keep in mind that changing a cranks sometimes means changing a bottom bracket too.
2009-09-15 4:54 PM
in reply to: #2407988

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Ventura County, California
Subject: RE: Crank arm length?

Crank length is both fit specific and purpose specific.
Given your ideal crank length, you might vary a little as follows...

Track bikes - shorter cranks for very high cadences

Road Bikes - fit specific usually, sometimes people who race a lot of crits will go shorter to allow a little more cornering clearance and to facilitate a high cadence.

MTB - Some use slightly longer cranks for increased climbing torque.

BMX - I know nothing about BMX, but I could see how you might want to go for really long cranks for more leverage since you start from a dead stop, sprint up to speed and only have one gear.

Given that you are 6'-2", you need 175's. 170's are too short unless you like to spin at super high cadences. 180's are not really necessary on a road bike.

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