What has the bouncing ball to do with tyres?

Manufacturer:Why does a rubber ball bounce? Why is this property important for tyres?
JohnWoon:When a natural rubber ball is dropped on the floor from a certain height, the impact or stress the ball gets when it hits the hard surface would force the rubber molecules to strain, stretch, reorganize or deform. This results in potential energy being stored in the molecules when the ball is in a state of strain. At the end of the impact i.e. when the stress is released, the rubber molecules would retract like a spring to its original unstrained state. The stored potential energy is hence recovered in the form of "bouncing" of the ball.

Natural rubber, being a very elastic elastomer, has good rebounce resilience. On the other hand, in semi-elastic rubbers such as Butyl, the bouncing recovery is poor at normal ambient temperatures as most of the energy is turned into heat on impact. (For this reason Butyl rubber is some times used for damping application)

But what has the bouncing ball to do with tyres?

During use, a tyre deforms as it moves and rolls through its contact with the road. As a result, heat is built up because the tyre is not 100% elastic. Other factors such as cornering and braking would further add to the heat built-up. As we all know, excessive heat built up in a tyre would lead to catastrophic failure.

As mentioned above, like the bouncing ball, the higher the resilience of the rubber, the lower would be the heat built-up. Fortunately for you and me, Natural Rubber has one of the highest resilience properties amongst all the rubbers available today. Therefore it is very widely used in the manufacturing of tyres, although it is sometimes blended with SBR (Styrene butadiene rubber) and BR (Butadiene rubber).

You should also take note that heat built-up increases with the size of the tyres. Hence we find natural rubber playing a vital role in heavy truck tyres and aircraft tyres. In the case of the aircraft tyres, a lot of stress is put into the rubber especially during landing and due to the ratio of their size to that of the aircraft, they carry quite a heavy load too.

Needless to say, natural rubber also happens to have other very important properties as far as the making of the tyres is concerned, that is, the building tack and mechanical strength compared to other rubbers!

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