Why is this bmx right crank arm thicker than the left?

[meb]

Had recently snapped a 1 piece crank so I replaced it tonight with a Mongoose bmx one piece crank.

The right arm is much thicker than the left arm on the direction of travel. So much so (perhaps 25-30 % thicker) that the unchained cranks will let the right arm fall to the bottom. This is a right side drive one piece crank.
Obviously it is much stronger that way, but why the right side arm which is not prone to failure rather than the left which is more prone to failure?

Is this somehow related to bmx course layout with the rider placing more weight on jumps on the right pedal?

 

[Jasper Janssen]

On Sat, 2 Jul 2005 16:35:19 +1000, meb
<[email protected]> wrote:

>Obviously it is much stronger that way, but why the right side arm
>which is not prone to failure rather than the left which is more prone
>to failure?

Actually, mainly because it's the right side arm which is prone to
failure. If your experience is the opposite I suggest it might be because
left side cranks are routinely made thinner.

Jasper

 

[meb]

On Sat, 2 Jul 2005 16:35:19 +1000, meb
<[email protected]> wrote:

>Obviously it is much stronger that way, but why the right side arm
>which is not prone to failure rather than the left which is more prone
>to failure?

Actually, mainly because it's the right side arm which is prone to
failure. If your experience is the opposite I suggest it might be because
left side cranks are routinely made thinner.

Jasper

If there is something unique to bmx cranks that causes the right to fail rather than the left as in most other bikes, what is it about the bmx that would cause the right to fail and hence a beefing up of the right side?


I've never had a right side failure, yet have broken several lefts.
On the left you are applying both a torsional load and a downward load at the same time. They are out of phase on the right, so all things equal, the left is more prone to failure.



Jobst alluded to the reason in this piece:
http://www.sheldonbrown.com/brandt/installing-cranks.html