Looked through the archives and Googled this one, but didn't find a
definitive answer.
How does a tire actually hold up a car?
At the Way Things Work site they talk about the footprint area of the tires
times the pressure equalling the weight of the car. However, if I look at
the forces: The road pushes up on the tires, but the tires must push up on
the wheels--with a force equal to the weight of the car (more or
less--depending on if you count the weight of the tires themselves). The
two factors I see as possible are 1) A pressure difference between the top
of the wheel and the bottom of the wheel--giving a net upwards force. Can
the pressure difference be enough? The effective area of 4-wheels is under
500 square inches--so you'd need a 4 lb/in^2 differential to support a 1 ton
car. The other--and I think this is the answer but need confirmation--is
that most (if not all) of the weight is supported by the sidewalls of the
tires which are stiffened by the air pressure.
Still the air-pressure times footprint area plays a roll--partially deflate
the tires and the footprint increases--but what about the sidewall forces
then?
A bit confused on this.....
Rick
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Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN
rtarara@saintmarys.edu
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