As ever rubber-ware is critical, the rubber compounds are carefully engineered with a range of other substances such as carbon powder and silicon and then heat treated to give it just the right properties. There is a hell of a lot of technology in that black stuff.
The tread pastern is designed with channels that pump water out of the contact patch area at an amazing rate, for instance an F1 rain tyre can pump out 80 liters per second, but the tread does a lot more than that. The flexibility of the tread blocks allows them to move and adapt to the road surface to find grip, winter tyres have lots of small deep blocks of soft rubber with extra tiny groves in them so they can even get some grip on ice. A lot of people in the UK don’t realise there are different tyres for summer and winter use, but in many countries swapping to winter tyres when the cold weather starts is compulsory.
Winter tyres don’t work so well in summer, at speed the narrow tread blocks wobble about and overheat which looses grip, so summer tyres have wider tread blocks with a shallower tread depth. Track day tyres go a step further and have fewer grooves and some of the tread blocks go right the way round the tyre.
The tread compound actually wraps round the microscopic lumps and bumps in the road surface to give grip. At speed the rubber molecules have to grab hold of the road then let go very quickly, softer rubber reacts faster and flows deeper into the road irregularities giving more grip but gets ripped apart more easily when it has to let go, so soft tyres wear faster.
Full on racing slicks have no grooves at all to maximise the contact area and reduce overheating. It still has a tread layer because the rubber compound that contacts the road is much softer than the rubber compound used the make the structure of the tyre.
The side walls have to be stiff enough to keep the tread section under control and the base layer under the tread layer needs to be strong enough to hold the tread securely and resist punctures. They are reinforced with cords of steel or Kevlar, the precise weave effects how the tyre deforms on the road and so effects handling. Generally track tyres are more supple but wear out faster and with only one or two plies are more prone to damage, by contrast tyres built for vans and trucks are harder with many more plies making them last much longer and resist damage at the expense of ultimate grip.
Stiffer or lower profile sidewalls give a quicker change of direction, but can’t follow rougher roads so easily and may skitter a bit, that’s why race cars don’t often use ultra low profile tyres. A taller and more flexible sidewall is better on poor quality back roads, but it also introduces a small delay making it feel slow to turn in and a bit vague.
A wide wheel holding a narrow tyre holds it very rigidly, which is great for flat smooth race tracks but stops the tyre adapting to rougher road surfaces. By contrast a narrow wheel on a wide tyre allows the tyre to move side to side and curling up at the side when cornering hard making the handling a bit sloppy. Excessively wide wheels in narrow tyres may allow the bead to be pulled off the rim, which is bad.
Changing the tyre pressure can transform a car’s handling. Lower pressures allow more flexibility but too low and the tyre looses control which is very dangerous. Higher pressures hold the tyre more rigidly, to high and it can’t react well and the handling becomes a bit wooden. The best grip level is somewhere in the middle, and it varies depending on the intended use of the car, a little lower for a comfy ride in a road car and a little higher if the same car is on a race track.
Tyres age, the first visible signs are tiny hair line cracks in the base of the tread blocks which means its past its best and in no use for performance driving, but it also perishes from the inside so old tyres should be avoided, 3 years for a track tyre and 6 years max for a road tyre is the norm. The tread rubber gets harder over time as it ages and also because it gets hot in use which reverses the heat treating process it was made with.
On a race car when the tread overheats the grip disappears very suddenly, this is called ‘going off’. If road tyres are required by the regulations the tread is cut down to about 3mm depth to minimise the heat generated by the tread blocks wobbling about. New race tyres are run through a gentle warm up and cool down first to settle the compound molecular structure, going straight out at full tilt on new tyres ruins them.
The tyre is the only thing that connects the car to the road, everything that the engine and suspension does ends up as a single simple force on each tyre’s tiny contact patch. Tyres effect the cars performance and handling more than any other single component, and its not just a case of bad tyres vs good ones, but its about choosing the right type for your car’s purpose.