Re: [Phys-l] Another tire question

[Rick Tarara <rtarara@saintmarys.edu>]

The May article makes things clearer.  The 'trick' here is to separate the 
tire into a top half and a bottom half.  The tension of the bead pulling on 
the wheel is uniform around the wheel with the wheel off the ground, but 
when on the ground two things happen to the bottom half of the tire.  It has 
an upwards force of the road (a portion of the weight of the car) and the 
deformation (bulging) of the bottom of the tire changes the direction of the 
pull on the bottom half of the wheel and the vertical component of the road 
force.  These two effects reduce the force of the bottom half of the tire 
compared to the top half by just the amount of weight that the tire must 
support.

That the road force can be considered to act only on the bottom half of the 
tire is, I assume, due to the flexibility of the tire.  That is, if the tire 
were really rigid, we would have to take the force to be acting on the 
entire tire, but then the rigid side-walls could support the weight through 
compression.

Rick

----- Original Message ----- 
From: "Bob Sciamanda" <trebor@winbeam.com>


> I resurrected two papers - in The Physics Teacher, not the AJP.  Both
> agree with Michael Edmiston:
>
> 1) "What holds up the steel wheels of an automobile?", W Shurcliff,
> TPT, 32, pg 296, May 1994
> 2) "How do tubeless tires support an auto?", J Sperry and E Jones, TPT
> 32, pg 174, March 1994
>
> Bob Sciamanda
> Physics, Edinboro Univ of PA (Emeritus)
> www.winbeam.com/~trebor
> trebor@winbeam.com
> ----- Original Message -----