n F understand that a smooth tyre gives
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a better coefficient of friction on a dry road than a tyre with a patterned tread. Is this correct and if so, why does a patterned tread have better anti-skid and braking properties in the wet?
AYes, a smooth tyre can give a marginally
better coefficient of friction on a dry hard surface than a patterned tyre, which has better anti-skid and braking properties in the wet because it provides channels for dispelling the water from the tread area and because the reduced area of rubber in contact with the road gives a higher unit pressure between tyre and road. The segments of the tread will therefore tend to break through the film of moisture on the road more readily than the large surface of the section of a smooth tyre that is nominally in contact with the road.
In practice the ability of a tyre tread to dispel water depends on the speed of the vehicle: the higher the speed the greater the likelihood that the tread will "float" on the water film. When the tread is completely waterborne the tyre aquaplanes.