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Re: [Phys-l] Another tire question

There's one detail that you may or may not consider important:
The rim of the wheel is shown grasping the bead, much as
parentheses grasp the o here:
(o o)

But I've never seen any such structure in a real rim. What
I see is more like this:
\o o/

Good point. I don't have equipment for mounting/demounting car tires to wheels, so I haven't closely examined the bead/tire seal. On the other hand, I have experience with "clincher" bicycle tires where the bead is grasped by the rim. If car tires are different, then I goofed that part.

I'm not opposed to saying that in some sense the car hangs
from the bead, but AFAICT it is cradled by the bottom bead
rather than dangling from the top bead.

Right. I actually intended that also, but I didn't say it well. I imagined the wheel both hanging from the top bead and also cradled by the bottom bead. That is, the weight is all supported by the bead. I thought some was hanging support and some was cradling support. If the bead is not clinched by the rim like my bicycle, then I guess the wheel is cradled only.

But that was not my major point. The major point I wanted to make was that the upward force on the bead is coming from the top sidewall, not the bottom sidewall. The car is not supported by the bottom sidewall. Rather, it is hanging from the top sidewall. I think the bottom sidewall is actually pulling downward on the bead, just like the top sidewall is pulling up, and the right sidewall is pulling to the right, and the left sidewall is pulling the bead to the left. The bead is everywhere being pulled outward by the air pressure acting on the sidewalls.

Then, to create a net upward force on the wheel, the upward pull on the bead from the upper sidewall must be more than the downward pull from the bottom sidewall.

Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
1 University Drive
Bluffton, OH 45817
419.358.3270
edmiston@bluffton.edu
.buffalo.edu/mailman/listinfo/phys-l