From: Peter Jon White <lists@peterwhitecycles.com> Subject: Re: [CR] Re: <http://search.bikelist.org/query.asp?SearchString=%22Re%3A++Wheelbuilding%2 2&SearchPrefix=%40msgsubject&SortBy=MsgDate%5Ba%5D> Wheelbuilding
KO Kevin wrote:
The way I learned decades ago was that crossing the seam keeps the seam pulled together, and was especially important on old Super Champion rims. Now this may be a myth, but since crossing the valve is only a slight (if any) inconvenience, I have always crossed the seam on 32-hole builds.
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Oh, it's a myth all right. While the four spokes adjacent to the joint angle away from the joint in a 32 spoke wheel built in the normal fashion, the spokes just further away from the joint angle back across the joint. The combination of spokes angling one way and then the next is to place a radial loading on the rim which pulls the joint together. A properly tensioned 32 spoke wheel requires an enormous amount of force to move the joint.
But one doesn't need to understand the theory of how a tensioned spoked wheel works. All one needs to do is observe the dearth of 32 spoke wheels using pinned joints pulling apart at said joints to know that it's a myth.
I'm not sure it's a complete myth. If the rim were struck sharply on the seam (as in hitting a curb), I can visualize a crossed seam staying together better than an uncrossed one. No data, or even anecdotal evidence to support this. However, I also believe in chaos theory, that everything has an effect, and I can only conclude that crossing at the seam must have at least a marginally positive effect. If there is some marginal benefit (and I do believe there is) I'm inclined to seek out that benefit, especially when what I'm giving up is mere convenience, and even that is debatable, as crossed spokes has never kept me from inflating a tire.
Now if someone can show me the negative effect of crossing the seam, I'll reconsider, but then that may force me to build 36-hole wheels with crossed valve-holes!
Kevin