Re: Amazing Facts

[Mark Sylvester <msylvester@gn.apc.org>]

> > From: BACHMAN@rfmh.org

> > 2. There was a passing allusion to the pressure in a tire being the
> > pressure exerted on the roadway. Normal tire inflation "prestresses"
> > the tire walls.

I presume this means that it keeps them straight and hence more 
rigid, so they support more force than when uninflated.

> > An inflated tire suspended off the roadway exerts
> > zero pressure on the road.

True, but why is this relevant?

> > The curvature of the tire walls provide
> > the equilibrating forces.

I find this difficult to digest in terms of physics.

As I understand it, then, for something like a bicycle tyre, 
which is pretty floppy without air inside, it would be fairly 
accurate to say that pressure on roadway = pressure in tyre, 
whereas for a truck tyre, which requires quite some force to 
collapse it, even when uninflated, the rigidity of the tyre 
walls makes a significant contribution to the force it can 
exert, so the pressure on the road can exceed the pressure in 
the tyre. Is this it?

Mark. 

Mark Sylvester, Duino, Trieste, Italy.