The tyres are one of the most important aspects that determine the handling characteristics of a race car. They are the only form of contact between the vehicle and the road surface; all acceleration, braking and turning are transmitted via longitudinal and lateral forces through them. Tyres are incredibly complex, but the basics can be described fairly simply.
Tyres are produced from a chemical compound made of primarily natural and synthetic rubbers, along with a myriad of other artificial fibres. These rubber blocks generate 'grip', by reacting with the ground. This is done through:
Friction - the typical reactive force that allows any two objects to interact with one another, such as rubbing your hands together.
Interlocking - where the slightly soft rubber compound will deform from its usual circular shape, to wrap around micro-bumps and depressions on the road surface.
Adhesion - as the tyre gets up to working temperature, they can become 'sticky', and can glue itself to the road (think of how you may pull your fingers apart from one another if they have been stuck together with glue).
The resultant of summing these together is how we describe the 'grip' of a tyre. A tyres grip will change and evolve depending both on the temperature of the tyre and their pressures - this is known as a temperature or pressure window, where the tyres will be working at their optimum (too high or too low can reduce grip). You may have heard F1 commentary talking about how 'team X is struggling to switch on their tyres' or 'team Y suffers a lot with overheating'. This means that the teams are struggling to either get their tyres into the optimum temperature or pressure window, or they are struggling to keep it in that window, and hence are loosing performance through loss of grip.
Tyres can loose grip over-time as they wear out, as the extreme forces (especially laterally through cornering) generate heat, along with the tyres slightly sliding as they skip over the road surface (this is a very simplified explanation!). At this point, small sections of rubber may begin to tear from the tyre, as these forces start to dismantle the surface compound. These little pieces can then stick back to the tyre itself due to its adhesive properties, creating a bubbly, rough surface. This is known as graining. This is minimising the effective area of contact between the car and the ground, and hence reducing the available grip. Depending on the championship, it may be important for a driver to manage their tyres, in an attempt to make them last for as long as possible. This means driving in such a way to reduce the affects of graining and other wearing properties on the surface, in order for them to last longer. This is done by minimising scrubbing of the tyre (minimising the lateral forces on the tyre that cause the car to understeer or oversteer).
This is a heavily worn tyre, with the graining and blistering of the tyre clearly visible.
Source: Race-car Engineering
Another variable is the actual compound that forms the specific tyre in question. Some racing series have tyres of a range of rubber compounds, and are usually described on a scale of softer to harder. Softer tyres are quicker to heat up, and are physically easier to deform, increasing the grip produced from interlocking and adhesion. However, this comes at the cost of the tyre wearing out much faster, graining quicker and ultimately resulting in reduced grip over a longer stint. On the opposite end of the spectrum, harder tyres are tricker to get up to operating temperature, and have slightly reduced grip as they are exhibiting interlocking and adhesive properties to a lesser extent. However, this allows them to last much longer than that of a softer compound tyre.
There are also different types of tyres for different conditions. For circuit racing, tyres can broadly be categorised into 'slick' and 'treaded' tyres. Treaded tyres are like those you see on road cars, and have spaced channels between the surface edge of the rubber. This is to displace water and dirt, allowing the tyre to grip up in a variety of conditions. Slick tyres have no tread, a smooth surface around its full circumference. This makes them extremely grippy when out on circuit (provided it isn't raining!). For when it is raining, race cars will too use treaded tyres (also known as 'cut' tyres or 'wets'), which like a road car, can displace the water underneath the tyre as it moves over it. The full wet, blue-striped Formula 1 tyres can displace 85 litres of water every second at 300kph. That is around a bath-tubs worth of water, on each tyre, every second. Without tread, the tyres wouldn't actually make contact with the asphalt, and will sit on a layer of water, providing approximately zero grip. This is known as 'aqua planing', when a car skips across the surface of water without making contact with the ground.
Above is a Bridgestone Formula 1 'Intermediate' tyre, which as the name suggests, sits somewhere in-between a full wet tyre and a slick one.
Now that was a brief introduction to tyres on race cars! Tyres are incredibly complex, and can be researched in far greater detail than outlined here. This includes different construction methods (cross vs radial ply), the anatomy of the tyres themselves (the carcass from the wearing surface), and even more that I don't know! The next blog post will be for Formula 1 fans, as I'll be discussing some of the technical regulation changes that are happening for the 2022 season, and how it could mix up the grid for an incredibly intense season! If anyone has any questions, you can always reach out to me directly, here or on socials!
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