When it comes to getting the most performance from your car, most drivers assume it is down to having a powerful engine, huge brake discs and a hard suspension system that can support the vehicle through curves at high speeds.
When it comes to manoeuvrability and grip, many people instantly attribute this to the suspension system alone. This is often highlighted by the numerous drivers opt for lower suspension, making it harder, with the expectation of achieving a better driving experience.
Yet, as far as grip is concerned, the deciding factor is the car tyre.
Tyre grip is very important in supporting your car’s other parameters.
Unfortunately, few people realise how important their tyres are, instead focusing solely on the car’s struts and springs. Ultimately, when it comes acceleration, braking and the centrifugal forces encountered on a curve, these are all transferred through the tyres and the relatively small contact patch they have with the road.
This misconception can be most seen when looking at cars customised for street or amateur track racing. These vehicles sport powerful engines, high spoilers, custom suspension and big, efficient brakes - all of which are expected to provide excellent grip. Yet they often overlook their tyres and, ultimately, all of these parameters (as well as the components that cost a small fortune) will have to be transferred through a little patch of black rubber, anyway.
What is grip?
Grip is the friction between two surfaces - in the case of tyre grip, between the tyre tread and the road surface. This is not a constant value, as it depends on temperature, pressure and, most importantly, the slipperiness of the road. Interestingly, we get the highest grip values when the tyre skids slightly.
Tyre grip occurs between the tyre and road surfaces.
Why does this happen?
The explanation can be found when looking at this phenomenon more closely. Rubber interacts with the road in a very specific way, since tyre grip is influenced by another phenomenon called adhesion. This occurs when the rubber molecules are in direct contact with the surface. Rubber is a polymer, while asphalt has a crystalline structure. When both of these structures meet at high speeds, the rubber molecules deform. Some bonds are broken, while others are created, and this process repeats in a cycle whenever one surface is dragged on the other. Such breaking and compressing of the molecular bonds absorbs energy, which is the force of adhesion. This force peaks when the difference in speeds is within 0.03-0.06 metres per second.
Why does the best tyre grip occur at the verge of skidding?
When the speed difference is greater, adhesion gives way to hysteresis, a derivative of tyre surface deformation. In the process, some areas of rubber are compressed, while others are stretched. In order for this stretching to be possible, the rubber atoms have to move relative to one another. This process is accompanied by friction, which heats the tyre. It also absorbs energy, in a manner similar to adhesion, but this time it is referred to as internal friction.
So, why does the highest amount of grip occur when you are on the verge of skidding? The rubber mixture is soft, while the road surface is smooth and heated. This is when adhesion forces dominate the contact patch and make the tyre ‘claw’ into the tarmac.
When will the grip be highest?Ideal tyre grip happens when we travel at the verge of skidding (or even slightly over it), the rubber mix is soft, the road surface is smooth and heated.That is when adhesion forces dominate the contact patch and make the tyre "claw into" the tarmac.
A practical example
Let’s get back to the issue of a car taking a curve at high speeds. The faster we travel, the greater the centrifugal force is. The car transfers its weight through springs and shocks, absorbing sudden movements and increasing pressure on the road.
Tyre grip is the product of tyre friction and down pressure. This down pressure is increased in curves, as it is provided by the centrifugal force, which transfers the weight to the outer tyres. In order to achieve high performance, the friction between the tyre and the tarmac has to be equally high, especially considering the centrifugal force that has to be balanced by the grip provided on a postcard-sized patch of rubber (the average size for a tyre’s contact patch).
Race vs civilian tyre grip
Of course, cars have different needs between the road and motorsports. Each sector has its own unique requirements and conditions, but grip is still important.
Race tyre grip
Race drivers understand that tyres are vital for securing good grip, so the right tyres can readily help them achieve better results. There are often claims that, when it comes to good vehicle-track compatibility, around 75% of this si down to the tyres. Suspension settings, brake balancing and the correct gear all fall far behind in this list. After all, what use is power and speed if you cannot carry it through a curve?
Racing tyres can be better dedicated to specific situations.
With this in mind, tyre manufacturers are often trying to improve their rubber compounds, finding a mixture that provides the best parameters in these circumstances. Obviously, every parameter has to be a compromise, since good tyre grip and durability cannot not be combined. Hard tyres, for example, can be driven for a long time without replacement, while their grip is lessened as a result.
A tyre that offers good grip will be made of a very soft mixture and will, consequently, wear out much more quickly. IT will also require a higher working temperature, which is why F1 drivers often have to heat their tyres.
You should also remember that racing tyre manufacturers often have it easier, as their tyres are only required to work in very precise, specified conditions. Every mixture has an optimal temperature range and will be immediately destroyed when they are exceeded, or it will lose all of its tyre grip. The relationship between durability and tyre grip is also obvious, as no one really cares that a tyre with better grip will wear out faster.
When rain appears, drivers immediately change to wet tyres and, furthermore, if the rainfall is not that heavy, intermediate tyres are also used.
Civilian tyre grip
So, what about tyres produced for everyday use? Manufacturing civilian tyres is a much harder task, as these products must combine good grip, as expected by users, with a longer durability.
Furthermore, the tyre has to behave well in the rain, as well as a cross a wider range of temperatures. In order to meet these needs, engineers often work for years, developing new compounds and tread patterns that offer the best compromise between these conflicting parameters.
Civilian tyres need to meet a broader range of requirements.
In reality, of course, there is no ideally universal tyre, which will perform well in all circumstances. This is why a sports tyre, designed to operate at a higher temperature, will not work well at 10°C, whereas a universal tyre will retain its characteristics. Similarly, the numerous pleas from manufacturers to use winter tyres are not groundless. Creating a tyre that will work in such a wide range of temperatures (from +60°C to -20°C) is simply impossible. The cut-off temperature before summer tyres lose adhesion is around 7°C. Winter tyre grip, therefore, works because winter tyres are designed to retain adhesion in ranges below this.
Tyre grip and road safety
A common argument amongst sceptics is that snow and low temperatures have always been around and people have always managed to, somehow, cope with them. While this is true to a degree, you should remember that the technologies available for manufacturing rubber compounds were limited and everyone was equally affected by poor performance at low temperatures. In other words, everyone on the road had poor grip. Things are much different today.
Imagine is a car ahead of you suddenly brakes. Using winter tyres, the grip is far more efficient than all season tyres or, even worse, summer tyres. The difference in grip and braking capabilities is noticeable, highlighting the need for products designed for the respective temperature range.