Tyre Dynamics - The Dark Art.

 The Dark Art

As we saw about the power unit in the previous week, We are going to look at something that is going to deliver the power from power unit. If you ask any engineer , what part of a car you don’t want to work on, his answer will be simple , TIRES . Yes , you read it correct. Tires are the most ignored aspect of a car when it comes to customer point of view , but it is a nightmare for engineers. Indeed tires are considered dark arts of Vehicle Engineering. This is because tires are the one part, that is made up of n number of assumptions. In fact, no two tire made up of same manufacturer of same profile is same . Let us look into them in this post.

Ever wondered, How a metal tube of maximum 5 inch could manage to take the part load of a car? But the honest truth is rubber made tires carry the full load of a car. Imagine how strong these tires had to made.  Tires are the only part that are in contact with the ground, which means , whatever has to be done in between vehicle with respect to ground , tires are responsible for it.

What if I say, Cars are not moving because tires are rolling? The tires used by cars are basically a rubber ( elastomer) which will distort its shape, that means it is not undergoing pure rolling. Which means they are under an influence of a resistance, this is called rolling resistance. This is caused because of Elastic distortion of elastomers and hysteresis ( Let us look in to this detail little later )

    Source: Fundamentals Of Vehicle Dynamics by Thomas D. Gillespie

When a tire rotate, there is a adhesion between ground and tire because of friction (static friction). When a force is given at the corner of tires, the tire tends to stick to ground , being a elastic material the force that comes from engine deform the tires. After a point of time, this elastomer have potential to come back because of elastic energy stored in it. ( slides back to the position , which produce heat, this loss is called hysteresis) . So to make it simple, movement of the elastomer in a tire can be compared with a caterpillar moving. So more the elastic behavior of tire, more it grips the ground (more rolling resistance) and move. You might ask me what is the relation between friction and grip is?. Imagine running in oily and normal floor, you got the answer.

Formula 1 provide 5 compounds of slick tires, and 2 compounds of grove tires. Slicks are basically those which won’t have thread patterns in it. As more rubber is in contact with ground more the elastic distortion, so more grip. While dry tires have less contact patch, and distortion will be less resulting in less grip. These tires are specially designed for racing, it can hardly last 200 km , while the tires that we use for passenger can last up to 20,000 km. This is because these tires are made so soft , so that it undergo enough elastic distortion. Softer compound means more wear. So these tires wear so much than the usual tires we use in passenger car.

Below given are the tire details

In upcoming post , we will look at influence of tires on performance of vehicles