Tyre contact patch + friction physics discussions

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Postby fivebob » Wed Nov 30, 2005 8:34 pm

crnkin wrote:Explain how the width influences the contact patch? Thats got me stuck

In theory, according to the equation A=Fn/P, for the same pressure and force, it doesn't :wink:

Area=width x length *not quite correct because the contact patch isn't rectangular, but for the sake of simplicity assume it is.

So if a 185 wide tyre has a contact patch length of 50mm, the area is 9250sq.mm, a 225 wide tyre would have a contact patch length of 41mm.

Now, because the wider tyre has greater lateral stiffness, you can run it at lower pressure and still have the same spring rate. So assuming the 185 was run at 200kPa, if you ran the 225 at 190kPa then it would have 5% greater contact patch area.

This assumes that the A=Fn/P equation holds true for all tyres, which in reality it doesn't always. However it is an observable fact that for most tyres a lower inflation pressure increases the contact area.

Also having a shorter contact patch means a larger adhering zone and a smaller slip zone, so even if the contact patch area remains the same, a greater percentage of it will be contributing to the available grip.

In short;

Wider tyres have more available traction
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Postby crnkin » Wed Nov 30, 2005 8:51 pm


I smell sausages

(thanks 5 bob)
kenny - "yours: 0hp @ 0rpm :D"
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PLEASE get moderators to fight your fights for you if you are a cock master
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