I bet with my friend that narrow or wide tires have more or less grip on ice or snow! I think narrow tires have more grip on snow and ice because the pressure is greater so the car hits the track more easily! But I don’t know the formula of grip so my question is. Do narrow or wide tires have more or less grip on ice and/or snow?
Answer
Dear Jordi,
If we only look at the theoretical approach to “grip”, neither of you wins the bet. The degree to which you get “grip” or “friction” between two objects (= the frictional force that one object experiences against another) depends only on two things: the normal (= perpendicular) force on the surface and the friction coefficient between the two materials. The latter is of course dependent on the two materials and with rubber ice it will be much closer to 0 than with rubber asphalt. Because the perpendicular force (= the weight of the car) is the same with narrow and wide tires and the coefficient of friction remains the same, the grip with wide tires will be the same as with narrow tires.
BUT rubber does not have a constant coefficient of friction. At low pressures (ie also with an equal force on a larger surface, as is the case with wide tires) the coefficient of friction is greater than at smaller pressures (0.67 compared to 0.5). So your friend wins the bet.
What else could be of influence? The material for example. Winter tires have a different composition than summer tires, so that the coefficient of friction for winter tires is greater. The degree to which your tires are inflated also plays a role: hard-inflated tires have a smaller contact surface (compare it with narrow tires) and will therefore slip more easily.
However, you can bet again with your friend, but instead of ice/snow you should talk about heavy rain. A car with wide tires will be more prone to aquaplaning (a film of water that sits between the tires and the road surface and behaves like a slippery surface), causing it to skid more quickly. However, this only has to do with the width of the tires and not with the coefficient of friction between rubber and wet asphalt, which is still greater at lower pressures (wide tires).
Hopefully you are not disappointed with this answer.
Bart
Answered by
ir. Bart De Schouwer
For my position I am the manager of a group of engineers who maintain production equipment. It is mainly with my ready knowledge (education, interests, …) that I could answer questions.
Kapeldreef 75 3001 Leuven
http://www.imec-int.com
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