Crash course

We sent Martin Klipp to learn how to drive a racing car. Here he tells us why the physics is so important.

Using physics to keep your car on the track.

To race a car properly you need to keep it balanced by controlling its weight transfer using the accelerator, brakes, and steering. Braking shifts weight to the front of a car and will making it physically dip forward. This can cause a reaction called oversteer, if the car oversteers too much the back of the car will loose grip completely and spin out of control and off of the track. The opposite to this is understeer caused by acceleration. This shifts weight to the rear which is why in a drag race you will often see the cars front wheels lift up.

The reason for this is down to physics. The effects of weight transfer are proportional to the height of the centre of gravity off the ground. Which is the reason why racing cars are generally lower than road cars. A flatter car, with a lower centre of gravity, handles better and quicker because the weight transfer is not severe as it is in a high car.

Sir Isaac Newton could have made a worthy Schumacher in his day. His laws of gravitation can be applied to racing:

A car in straight-line motion at a constant speed will keep such motion until acted on by an external force.

The only reason a car in neutral will not keep on going forever is that friction, an external force, gradually slows the car down. In this case the friction comes from the tyres on the ground and the air flowing over the car.
When a force is applied to a car, the change in motion is proportional to the force divided by the mass of the car.

This sounds complicated but it’s not Newton’s famous equation F = ma, where F is a force, m is the mass of the car, and a is the acceleration, or change in motion, of the car can explain this. Racing cars are made to be powerful and lightweight. So when a force such as the engine pushes them they move faster, a heavier car naturally reacts more slowly to forces. The more ‘F’ and the less ‘m’ you have, the more ‘a’ you can get.
 Every force on a car by another object, such as the ground, is matched by an equal and opposite force on the object by the car.

Braking in a car causes the tyres to push forward against the ground. In retaliation because of gravity the ground pushes back. As long as the tyres stay fixed to the car, the ground pushing on them causes friction and slows the car down.

The importance of tyres

Choosing the right tyres for the race is one of the most important variables to get right. The wrong choice will have the driver facing a near impossible battle against the elements. The racing tyre itself is constructed from very soft rubber compounds which offer the best possible grip against the texture of the racetrack, but wear very quickly in the process. If you look at the track, just off the racing line, a large amount of rubber debris gathers (known to the drivers as 'marbles'). All racing tyres work best at relatively high temperatures. At the highest level in Formula One dry 'grooved' tyres are typically designed to function at between 90 degrees Celsius and 110 degrees Celsius. To ensure that the tyre pressure stays as constant as possible during these changes in temperature a special mixture of low density gases is used to inflate them rather than air.

The weather also plays a key factor and more often than not it is down to a calculated guess or gamble to choose either wet or dry weather tyres. 'Intermediate' and 'wet' tyres have full tread patterns, providing the largest possible contact patch to the road, and maximises traction for any given tire dimension expelling standing water when racing in the wet. One of the worst possible situations for a race driver remains 'aquaplaning' - the condition when a film of water builds up between the tyre and the road, meaning that the car is effectively floating. This leads to vastly reduced levels of grip. The tread patterns of modern racing tyres are mathematically designed to scrub the maximum amount of water possible from the track surface to ensure the best possible contact between the rubber and the track.

At the other end of the spectrum a slick tire (also known as a "racing slick") is a type of tyre that has no tread pattern. Slick tires are usually made of much softer rubber compounds than treaded tires. The softer rubber gives greater adhesion to the road surface, but it also has a lower treadwear rating and wears out much more quickly than the harder rubber tires used for driving on the streets. In Formula One slick tires are no longer allowed, yet dry weather tires are still often referred to as 'slicks' as they have minimal tread pattern and similar behaviour in wet weather.