By Ian Lockwood
March 19 2008
Grip. A simple four letter word, which covers a complex and crucial topic so vital to the area of a race tyre and consequently making a race car go fast around a race track. So, what is grip? Essentially the word grip in a tyre context is used to describe the friction between the tyre and the track.
On the tyre side, how a tyre derives its grip, or its friction with the circuit, can be characterised in two main ways; adhesion and hysteresis loss by deformation.
Adhesion is where the tyre compound forms a chemical bond with either the circuit surface, or rubber that has already been laid down on the circuit surface. It’s the ‘stickiness’ of the tyre.
Deformation is where the tyre, or more particularly the tyre compound, can move to fit around the irregularities of the track surface. Energy loss occurs here and friction results. This also helps adhesion too, as the more a tyre compound is able to deform around the track surface irregularities, the greater the contact area for adhesion to occur.
“How a tyre gets its grip is a very complex topic,” explains Tetsuro Kobayashi, Technical Manager, Bridgestone Motorsport. “But it is also a vitally important topic as without grip our tyres would be useless.
“Tyre compound development is the most important area for us seeking grip from our tyres, and advancements we have made through developments for motor racing have benefitted our passenger vehicle tyres too.”
In developing its tyre compounds Bridgestone looks at adhesion by concentrating on the chemical makeup of the rubber. Changes in the polymers than makeup the rubber mean that the compound reacts differently to the track surface. Processing the data for compounds and track surface interaction consumes a lot of resource at Bridgestone’s technical centres.
How ‘soft’ the tyre compound is influences deformation, but the nature of the deformation is an important factor in the tyre design too.
“We must consider how quickly a tyre deforms and how quickly it regains its shape, both the tyre in its entirety and the compound too,” explains Kobayashi.
“How quickly the tyre in its entirety deforms and regains its shape is related to tyre pressure, tyre construction and rubber compound. The compound on its own is the primary consideration in the deformation around the track surface irregularities.
“A racing tyre compound deforms quite quickly but regains its shape quite slowly and this helps the tyre grip.”
Tyre wear is also an area where rubber compound is the focal point. “The compound is the greatest influence on how a tyre wears in this respect,” explains Kobayashi.
“How strong the rubber molecules are helps determine how the tyre wears and the harder the compound the less wear we will see.”
Formula One cars are very different from normal passenger vehicles as they have high levels of downforce because of their shape and the numerous wings attached to them.
“The downforce we can see from Formula One cars is a significant factor in how much potential grip is available, as the grip available increases as vertical load increases,” explains Kobayashi.
“Because this grip is not caused by the tyre we often see this termed as aerodynamic grip, whereas grip caused by the tyre itself is termed as mechanical grip.”
A tyre needs something to grip on to, and this is where the track comes in. Track surfaces can vary enormously, and not just between tracks, but even on a track which has been surfaced at different times or with different types of material. Two circuits which have identical layouts could require two very different tyres to get the best amount of grip.
“We look at track surfaces on a macro and micro level,” explains Kobayashi. “Macro is where we look at how the track surface is made up and how closely the stones that make up the surface are spaced. Micro is where we look at the roughness of the stones themselves.”
Grip is not the be all and end all of tyre performance, even if drivers always say they want more grip. Indeed, too much grip can be a bad thing. An extreme example would be a tyre so sticky that it requires an excess of torque to get the car moving.
Grip is never a constant, it is variable, and that’s part of what makes motor racing so exciting for the spectators, and so rewarding for the drivers. Tyres wear and their performance characteristics change, just as the track surface can change over the course of a race too. Another important variable is the weather, a change in track temperature can mean the tyre works differently too.
“Grip certainly never remains at the same level,” explains Kobayashi, “and this is an area where a great driver can make the difference over a good driver. A great driver will always maximise the grip at his disposal quicker than a lesser driver.”
The biggest change the weather can make to the grip of a tyre at a Grand Prix is when it rains. Water on the surface of a track changes the molecular bonding potential meaning that grip through adhesion diminishes and grip through deformation becomes more important.
“We do not see snow or ice at Grands Prix so rain is the biggest weather change possible for grip potential,” explains Kobayashi. “Water affects our tyres’ grip through adhesion, and this is why our wet and extreme wet tyres have different compounds to our dry tyres.”
Grip is a pretty interesting topic, and it’s certainly something that will be at the forefront of the minds of the 22 drivers who line up on the grid for the Petronas Malaysian Grand Prix at Sepang.
“Formula One drivers are always looking at how they can get the most grip from their tyres,” explains Kobayashi. “At Sepang, just as at every race track we visit, grip levels will be at the forefront of every driver’s mind.”
Source: Bridgestone Motorsport