Crank length

Road cycling & upcoming rides
Marco_A
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Joined: 12 Apr 2012, 20:22

Postby Marco_A » 12 Oct 2012, 15:08

Found a crack on the inside of one of my cranks so I'm up for some new ones! I'm actually going to do the whole drivetrain.

I'm after some advice on crank length. I found this:

http://www.machinehead-software.co.uk/b ... lator.html

Which says that my current crank length is no good. (172.5mm) I also found this:

http://www.nettally.com/palmk/crankset.html

Which says my cranks are fine! Any ideas?
Also, I'm currently running Dura Ace 7800 groupset but I'm open to suggestion for what to look for in a decent drivetrain. Budget is around $500 for the crankset.

Cheers!

shrubb face
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Postby shrubb face » 12 Oct 2012, 19:01

You should probably tell us how tall you are before we go any further....

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mikesbytes
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Postby mikesbytes » 12 Oct 2012, 21:24

What Alex means is the length of your legs.

But before you get too hung up, do some education on foot velocity. You will see that shorter cranks = higher cadence to provide the same foot velocity. To simplify the mathematics your looking at about one extra tooth on the big ring per extra 5mm of crank length or to put it another way. If you were using a 48t ring on your fixie with 165 cranks and you swapped to 175 cranks, then you would change to a 50t ring to maintain the same foot velocity.

AndrewBurns
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Joined: 11 Dec 2011, 18:47

Postby AndrewBurns » 13 Oct 2012, 04:51

In my experience crank length doesn't make any obvious difference within reason. I have 165mm cranks on the fixie, 170mm on the commuter and 172.5mm on the road bike. Between those three values I can't tell the difference.

Marco_A
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Joined: 12 Apr 2012, 20:22

Postby Marco_A » 13 Oct 2012, 15:11

Mike, I'll do some research on foot velocity. Thanks!

shrubb face wrote:You should probably tell us how tall you are before we go any further....


I'm 182 cm tall with an inseam measurement of 80cm.

AndrewBurns wrote:In my experience crank length doesn't make any obvious difference within reason. I have 165mm cranks on the fixie, 170mm on the commuter and 172.5mm on the road bike. Between those three values I can't tell the difference.


That's helpful, thanks Andrew.

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weiyun
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Postby weiyun » 13 Oct 2012, 17:22

AndrewBurns wrote:In my experience crank length doesn't make any obvious difference within reason...

Whilst there's logical paper reasoning based on biomechanics for matching crank length to leg length, there's no performance based experimental data to back up the theory. So it's a case of applying some common sense, logical belief and personal preference.

rhys
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Postby rhys » 13 Oct 2012, 19:50

Please post a picture of yourself astride your bicycle so that we may make educated assessments.

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weiyun
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Postby weiyun » 13 Oct 2012, 19:57

rhys wrote:Please post a picture of yourself astride your bicycle so that we may make educated assessments.

You can't be serious right? Differentiating 5mm crank length difference (or 3%) off a casual photo?

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Karzie
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Postby Karzie » 14 Oct 2012, 09:17

For what it's worth, my own opinion is that I've never been able to tell how long my cranks are (I used to be 6' 1'' ) without looking at the stamp. Seems to make a big difference tho' whether on some corners you can still pedal around them.

Don't put long cranks on a fixie.

rhys
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Postby rhys » 14 Oct 2012, 17:15

weiyun wrote:
rhys wrote:Please post a picture of yourself astride your bicycle so that we may make educated assessments.

You can't be serious right? Differentiating 5mm crank length difference (or 3%) off a casual photo?


Image

Image

Image

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weiyun
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Postby weiyun » 14 Oct 2012, 18:27

Thanks Rhys. That hook looked too nasty. :)


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