Extrinsic Factors Affecting Adhesion

It’s not only intrinsic factors inherent to a specific tyre such as rubber compound and construction that affect levels of adhesion. There are also a number of extrinsic factors that influence the CoF between the tyre and the road too. These must be understood to influence certain tyre dynamic behaviours into the racecar through the tyre.

Compound Temperature

The temperature of the tyre compound affects adhesion by increasing both the conformance and the penetration of peaks and valleys in the road into the contact patch. This also increases the rate of chemical reaction between the tyre rubber and asphalt, but only up to a point, after which the tyre will “go off” and grip levels reduce.

Inflation Pressure

Due to the flexible nature of tyre rubber, inflation pressure introduces deformation at the contact surface, ranging from a concave profile (low pressure) to a convex profile (high pressure). This affects the surface area of the contact patch. Somewhere in between the two is a flat profile which provides maximum contact area and the optimal adhesion. This is the goal of the dynamicist.

Interestingly, sometimes if teams are struggling for tyre temperature, they boost the tyre pressures which results in a convex profile and a very narrow contact patch. This contact patch heats up quicker, which then radiates throughout the rest of the tyre, increasing its overall temperature.

However, it is important to understand the properties of gas in that for a given volume, if the temperature increases so does the pressure – leading to a compounding effect of both reduced adhesion and reduced contact patch area.

Track Conditions

Variables such as track surface roughness, wet track, dusty track all influence the level of adhesion.