All car tyres may seem to be the same but they aren’t. Road tyres have different characteristics designed to maximise their performance for specific types of use. However, these differences pale into insignificance when you consider the different tyres offered for competition use.
Take rally car tyres. These must cope with a huge array of surfaces in innumerable different climatic conditions. In addition, rally car tyres usually have to be road legal and must last longer than racing car tyres.
Examining two types of rally car tyre in more detail gives an idea of how the various factors in the tyres interact. Gravel tyres have to clear away the top coating of soft dirt or loose gravel, just as car tyres must clear away rainwater. To do this, they have big, chunky blocks that are made of relatively soft rubber. This lets the tread’s blocks grip while protecting the reinforcing plies that lie beneath them. The tyre tread and carcass’s being rigid enough to resist tearing while being sufficiently elastic to return to their initial shape guarantee toughness and a long life.
Snow/ice tyres can boast an effective grip-enhancing addition. Some can have up to 380 carbide-tipped studs in their tread. This is tough on the surface beneath the tyre but the surface can be tough on the studs themselves. At 75mph, each stud hits the snow or ice 17 times…per second! The impressive part – other than that (most of) the studs are still present when the car stops – is that the car is running on a total of about 50 studs at any one time. The total area the studs offer is about the size of a postage stamp.
In some instances, the tyres have no tread at all. Such tyres are called slicks and are used in drag racing. ‘Top Fuel’ dragsters are the fastest and can reach 330mph in less than 4.45 seconds – the time it takes them to cover the quarter mile. Accelerating faster than the space shuttle launch vehicle or a catapult-launched jet fighter requires as much grip as can be found.
It’s common for all kinds of dragsters to do something memorable. The driver places the car so its rear tyres are sitting in two puddles of water laid down near the start of the drag strip. The driver then applies power, spinning the rear wheels in the water. The immediate result is huge clouds of rubber smoke and steam around the tail end of a car that’s standing virtually still at practically full throttle. Yet this isn’t for show. After a ‘burn out’ like this, the tyres’ tread surfaces are extremely hot and sticky – and therefore grippy.
Often, drag racing car tyres look distinctly soft as the car approaches the start line. This is unsurprising, as the tyre pressure used is around the 12 to 15 psi mark. Why so soft? For two reasons. Soft tyres give better grip but they have another benefit. As the wheels rotate faster, the tyres enlarge. This is like putting bigger wheels on the same car; drivers get a higher top speed from the tyres’ radial expansion.
As you can see, even from just these two forms of motor sport, specialist car tyres are essential. They do what’s asked of them and in doing so, they increase the performance of the car involved in whatever sport is concerned. Think about this the next time you find yourself believing car tyres are all the same!