Don Ferris wrote:
>If I do a bit of mental gymnastics to put this all in perspective (in my
>mind anyway), the cam closing action on a skewer cannot generate any more
>clamping force than the yield strength of skewer rod itself. Most skewers
>are about 5mm in diameter. Assuming the material is equal in yield strength
>to 4130 chromoly steel, about 75KSI, that gives a potential of yield
>strength on a standard steel skewer of around 1,610-pounds based on the root
>dimension of the threads (4.2mm nom.). Since the skewer must clamp both
>dropouts using a common rod, total clamping pressure is equalized over both
>dropouts. If we assume the same properties for a 4130 track axle and nut of
>standard dimensions, 10mm, then the potential clamping pressure is limited
>by the root dimension of the axle threads (8.8mm) and its ability to resist
>tightening stresses, preload, and external load. That'd be about
>7,000-pounds and since each nut clamps each dropout between itself and the
>face of the axle, that's 7,000-pounds per dropout. You can give or take a
>few ksi for stuff I didn't account for, but I think that's pretty close.
There's a fundamental fallacy in that argument.
Yes, if you manage to overtighten a QR skewer, the skewer rod will snap, but that is not the failure mode of an overtightened nut.
In the case of a nutted hub, overtightening will result in stripped threads, not a snapped axle. This failure will occur well below a stress level that is at risk for snapping the axle.
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