Old 07-30-15, 08:58 AM
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Bikes: 1982 Bianchi Super Leggera

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Originally Posted by FBinNY View Post
The entire hanging from top, supported from the bottom debate is nonsense, there are elements of truth and error in both statements.

First, let's end the supported from the bottom error. It's not possible, for the simple reason that the nipple isn't attached to the rim, and the rim can't push it toward center. Try that with a single spoke in a hole of some kind and it'll be obvious.

But the hanging form the top theory is likewise weak. If you press the axle of a built wheel toward the rim, you won't see enough change in the tension of the spokes opposite (the top) to account for the force involved.

Instead of thinking inn terms of either wrong answer, think of a wheel as a system where ALL spokes support the hub at all times. When loaded, the tensions in the various spokes change so there's a net change among the spokes to offset the load. How that change is represented among the individual spokes depends on the radial stiffness of the rim.

Looking at extremes helps. If we assume the rim is absolutely rigid (radially) there will be a reduction in tension among lower spokes, and a symmetrical increase among upper. But if the rim has very little radial rigidity, the area directly above the bottom spoke will move in slackening that one spoke, while then rest will have a very small increase in tension distributed nearly equally all the way around. The reality is that rims are in between those extremes, so you get a blended result, with it looking more or less like one of the extremes according to the rim's ability to spread the load.
I understand and agree with this totally.

I was just trying to break it down to the simplest form but I may have gone just a little too far. My main point was that spokes don't (for all practical purposes) support a load in compression.

Last edited by KJK; 07-30-15 at 09:01 AM.
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