Re: [Phys-l] Another tire question

[John Denker <jsd@av8n.com>]

On 11/06/2007 02:09 PM, Rick Tarara wrote:
> OK--now it seems we have two competing models--if I understand the replies. 
> Both involve the sidewalls/beads and the tension (not the stiffness) due to 
> the inflation.  One model says that the tires push up on the wheels through 
> the beads, and now Michael's answer that the tires pull up on the wheels 
> through the beads.  I can sort of see it either way--but which is it?

It comes to the same thing, really.

If you imagine that the tire is stitched and/or glued to
the rim, you wouldn't need a bead, and the tension would
be passed directly from the tire to the rim.

But the way it is actually done nowadays on cars, there
is indeed a strong bead, and that mediates some adding
and subtracting of tension.

It's kinda like asking about the energy of a particle in
a square well;  you can measure delta E down from the top
or up from the bottom.

The *simplest* version is the one I gave, imagining that
the tire is stitched and/or glued to the rim.  But it is
incomplete in the unstitched, unglued case.

The bead story as stated is incomplete, because it didn't
say how the tension in the bead can "adjust itself" to
handle the load.

The two together makes a more complete story.