Barcelona - a unique test for tyres 04 May 2004
Tyre energy and tyre wear - the difference explained
High corner loadings combined with a very abrasive track surface make the Circuit de Catalunya particularly tough on tyres. It is, in fact, what might be termed a classic tyre circuit a strong contrast to new venues such as Sepang, which possess a very different type of track surface, even though they may too see high tyre energies.
High tyre energies? When discussing tyres and how they perform at a given circuit, the concepts of tyre energy and tyre wear must be distinguished, as Renaults Executive Director of Engineering, Pat Symonds, explained ahead of this weekends Spanish Grand Prix.
Tyre energy is a measure of the total work a tyre must do, and represents the sum of the energy requirements produced during cornering, braking and under traction. While these are separate forces, generally acting in separate directions, they act in combination with each other, as a driver is typically braking and cornering, or accelerating and cornering, simultaneously. This total energy is a good measure of how hard the circuit is going to be on tyres, and the requirements can be divided up to give a separate figure for each tyre, indicating which corners of the car are under the most load.
Thus, at Barcelona, the hardest worked tyre is the left rear. Assuming the total energy of this tyre to be 100%, the right rear requires 86%, the left front 63% and the right front 42%. These figures allow us to draw some basic conclusions about how the tyres work in Barcelona: the left front works 150% harder than the right front, owing to the clockwise direction of the circuit and long right-hand corners such as turn three. Equally, the other major difference is between the energy requirements of the front and rear tyres: even though Barcelona is a particularly tough circuit on tyres, and especially the left front, the requirements of the front wheels are still only 56% of the total energy of the rear tyres: this gives some measure of the energy demanded by traction and controlling engine power.
Aside from tyre energy, essentially how hard the tyres work, teams must also take account tyre wear, which is a measure of how the tyres suffer from their interaction with the track surface. The way a tyre grips the road is about much more than just friction. Being relatively soft, a tyre can deform into the roughness of a track surface such that there is a mechanical locking which adds to the pure friction. In fact, there are even forms of bonding and inter-molecular attraction between the tyre and road surface essentially, chemical reactions take place under high loads which combines to make the subject of tyre wear an extremely complex one.
It is perhaps too obvious to state that soft tyres on a rough track will wear more than hard tyres on a smooth, low-grip surface. But what other factors can have an influence?
Firstly, different cars and even different suspension settings on a given car affect the tyre wear. Every car owner knows incorrect suspension alignment can cause excessive tyre wear, but with a racing car, alignment is optimised for total performance: this may or may not, depending on the design philosophy, accelerate tyre wear.
Fundamentally, the wear on a given compound is a function of a coefficient that encompasses both the car design, and the road surface characteristic multiplied by the square of the total tangential (lateral or longitudinal) force acting on the tyre, and divided by the load on the tyre normal to the tyre contact patch. In other words, the faster you go, the more the tyre wears no surprise there! Indeed, these days, most people expect tyres on their road cars to last over 20,000km. On an F1 car at Barcelona, we would be looking for a life of around 90km.