# Measuring Crank Size?? How do you measure 170MM



## edesros168 (Aug 21, 2007)

Hey all I am looking to upgrade to an XTR crank. My new 08 Fuel EX5.5 has the Shimano M442 Octalink. I see XTR cranks with 170-175MM crank sizes?? From what pints on the crank to I measure. Measuring from end to end of the arm I got 203 mm and from center of the screw to center of the pedal input I got 171 MM??


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## monkeyfist23 (Dec 7, 2005)

I believe the size of your current crank arm will be etched into the crank arm somewhere on the inside...


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## aka bubba (Jul 12, 2006)

Look on the inside crank arm of the drive side.


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## Shayne (Jan 14, 2004)

*Measure...*

From the center of the BB spindle to the center of the pedal spindle.
Sounds like you have 170mm.


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## sacredny (Aug 10, 2007)

edesros168 said:


> Hey all I am looking to upgrade to an XTR crank. My new 08 Fuel EX5.5 has the Shimano M442 Octalink. I see XTR cranks with 170-175MM crank sizes?? From what pints on the crank to I measure. Measuring from end to end of the arm I got 203 mm and from center of the screw to center of the pedal input I got 171 MM??


The measurement is centre of pedal thread to centre of crank thread (or centre of hollow) - I'd guess you have 170's unless you have a dodgy tape, or eyes


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## Sprocketeer (Feb 22, 2004)

I think standard stock is 175mm (145mm for women's design bikes). I bought 172.5mm XT cranks in Japan and it was a world of difference. I don't think you can find that size in the States though--increments of 5mm only.

Shimano marks the size on the inside of the crank arm.


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## JonathanGennick (Sep 15, 2006)

edesros168 said:


> and from center of the screw to center of the pedal input I got 171 MM??


You probably have 170mm cranks then. You probably just made 1mm error to get to 171mm. 1mm is not much, and it'd be easy to be off by that much when just eyeballing a tape that you probably can't hold precisely on top of what you are measuring.

So far as I know, the most likely default crank sizes on off-the-rack bikes are 170mm and 175mm. All of my cranks are one or the other of those two sizes.

BTW, if you are upgrading your cranks, there is no rule that you have to stay at the same size. You could move up/down a size if you wanted to.


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## DeeEight (Jan 13, 2004)

Some companies have offered cranks that were 1mm higher than normal, just to stand out from established companies. Cook brothers cranks for example came 171, 176 or 181mm. Bullseye made just about any length you could want including some over 200mm. But by and large the usual range is from 165 to 180 in 2.5mm or 5mm (depending on product level) increments as far as Shimano, Campagnolo, Suntour, Truvativ, FSA and Raceface go.


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## FL_MTB_Weekend Warrior (May 21, 2007)

Here is a visual representation... I went through the same thing...










Look at the end of the crank arm where the pedal screws in... (this is a 175mm crank arm)


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## edesros168 (Aug 21, 2007)

Thanks all for the help, I do indeed have a 170 didnt realize that it was printed on the arm. What would be the benefit from changing to a 175MM arm?? Also do I just have to buy the crank or do i also have to buy other things to do this upgrade??


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## FL_MTB_Weekend Warrior (May 21, 2007)

When I bought my M970 crankset, it came with everything I needed...even tools.
All I needed to get were tools to remove the old crank arms and bearing...


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## edesros168 (Aug 21, 2007)

So what's the benefit if any to cahanging to a 175 from 170 mm arm??


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## gumbymark (May 25, 2007)

Benefits are dependant on your height. If you don't feel right on the 170s a change to a longer arm might help. You can standup and crank harder on a longer crank arm but oddly enough, you will smack the pedals into more things on the track. 

Changing the crank lenght is done to try to match your most efficient pedaling dynamics.

It depends on you and you only.


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## edesros168 (Aug 21, 2007)

Well seeing as I am 5'6 I can't see me needing the 175's


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## Anonymous (Mar 3, 2005)

I can't believe nobody has dropped a bad joke by now. 

Crank Size?!?!? :eekster: 

Come on, let's not forget the third grade people. We start to grow old when we stop playing!


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## f3rg (Aug 29, 2007)

I'm 5'6" and I ride a 175. It feels perfectly normal to me, but that could just be because I'm used to it after all these years. My wife's bike is the same size as mine but has 170mm cranks, and they feel odd to me.


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