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Rotation Direction

Why do racing tyres have a direction of rotation?

Author: SuperUser Account/Friday, January 15, 2016/Categories: Technical Information

All racing tyres (and tyres in general) are produced in basically the same way. One of the final steps before the tyre is cured in the mould is to apply the tread rubber to the casing.

There are 3 ways that the tread can be applied before the raw casing goes into the mould:

1. The tread can be 'wound' onto the casing in a continuous strip about the thickness of a pencil, gradually building up to the depth and profile required. This type of tread can be run in either direction.

2. The tread can be applied in 1 single solid piece, about 2 metres long and joined in a 'butt' joint (ie the joint is perpendicular to the tread surface). This type can also be run in either direction.

3. The tread rubber is produced in a long strip and is wrapped around the tyre and joined in one place, called the 'splice'. it is at an angle of approximately 45° to the tread surface. In order to keep this joint from peeling open under severe acceleration or braking, it must be run in the correct direction. This is by far the most common technique for both road and race tyres.

The force on the tread from acceleration is much greater than that from braking, so direction of rotation on drive axles is considered to be more important.

For rear wheel drive cars, the solution is simple. The front wheels perform only braking, which has an opposite force on the tread join to the rear wheels acceleration.

On front wheel drive cars it is opposite. The rear wheels only brake, whilst the front wheels mainly provide acceleration. Certainly the front wheels also provide the majority of braking, but on balance the acceleration force is greater and more constant.

And of course 4 wheel drive cars have all wheels the same as front wheel drive.

To assist in correct fitment, most race tyres have an arrow on the sidewall, indicating which direction the tyre should rotate on the drive axle (refer illustration).

Some have two opposing arrows indicating the correct direction whether fitted to the drive or driven axle. Some have no arrows at all, but rely on other markings. However care should be taken with all tyres, especially on the drive axle.

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