Jay Somerset
Guest
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 Posted:
Tue Dec 28, 2004 10:43 pm Post subject:
Re: A4 tyres |
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On Mon, 27 Dec 2004 23:09:43 GMT, Peter Bell <peter@invalid.org.uk> wrote:
| Quote: | In message <1gpgy7a.1w3htv7no53ayN%steve@italiancar.co.uk
steve@italiancar.co.uk (SteveH) wrote:
I'm obviously being a bit thick here, but could you please explain how
a, for example, a 185/60 tyre will put the same area of rubber down as a
220/45?
One will have a long thin footprint, the other will have ashort fat
footprint.
Think about it - it's the air in the tyres which supports the car, and
the force between the ground and the tyre provides that support. If
there is 500lbs weight bearing on one wheel, and the air pressure in
that tyre is 50lbs/sq.in., then it will take 10sq.in. of tyre surface to
take the weight, therefore the area of the contact patch will be
10sq.in. Whether that tyre is one inch wide, or ten inches wide, the
surface area in contact with the ground will still be 10sq.in.
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This is correct theoretically, but assumes that the tire tread and sidewall
are infinitely flexible. Actually, they are not.
Lowering tire pressure will certainly increase the contact patch, but if it
is long & narrow, then the tread will buckle, raising the center line of the
tire and reducing traction. If the contact patch is short & wide, then a
given decrease in pressure will cause less tread distortion.
The net result of all this is that low-profile, wide tires can run with
lower pressures than high-profile, allowing the contact patch to be
maximized without tread distortion, and consequent loss of adhesion. |
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