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Dishing and resistance to lateral loads

ergott said:
Wheels don't fail because of their dish. The reduced dish of an offset rear rim adds to the lateral stability of the wheel.
But don't wheels fail due to lack of lateral stability? Dishing decreases wheel strength to lateral loads from the right. A dished wheel is more likely to taco than a non-dished wheel.

If you compare an MTB hub with road hub, with few exceptions you'll see that they have the same distance between flanges - the difference is that the MTB hub has longer axle stub on the left side, moving both flanges laterally to the right to decrease dish. This better balances wheel strength to lateral loads from either direction (i.e. it trades off some of the strength to loads from the left to increase strength to loads from the right).
 

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Unsupported spans of spoke bed

alienator said:
You're making a pretty large assumption, here, that it was the fact that the rim had offset spoke holes that caused the failure. That, unfortunately is not in evidence, nor is there any reason to believe that is the case.
I don't think its that large an assumption. The Mustang rim has a relatively wide, flat spoke bed. Moving the spoke holes to the left increases the width of the unsupported spoke bed to the right of the eyelet, increasing the bending stress between the eyelet and the sidewall, and this is exactly where the cracking can be seen in the photo.

Many other OCR rims are V-shaped, where the sidewall angles in a more direct line to the spoke hole, so there is less bending stress experiened in the sidewall. As mentioned, still other OCR rims have a rib connecting the wider span of spoke bed to the outer rim wall, also decreasing the bending stresses.

The large bending stresses generated from spoke tension on wide, flat spoke beds is what generated the need for spoke washers, eyelets and sockets (double eyelets), to better distribute spoke loads and decrease localized bending stresses. Forming the rim into a V-shape, so that spoke loads are more directly tranferred to the sidewalls also decreases bending stresses. Simply moving an eyelet sideways in the spoke bed, without reinforcing or increasing support of the widened span of spoke bed, may indeed increase the likelihood of cracking the spoke bed.
 
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