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Wheel coatings

Controlling tyre temperature is of vital importance to the performance of a modern Formula One car – or any racecar for that matter – with teams constantly striving to get the most from each tyre compound they use over a stint. Controlling the heating and cooling cycles a tyre is subjected to helps provide more consistent performance. Recently, some teams have begun to use a coating on their wheel rims in an attempt to transfer more heat into the tyre, in order to reduce the amount by which they cool on the straights between braking and turning events.

To date, it is thought that Ferrari, Red Bull and Mercedes are all using such a coating. It is also thought that the coating in question is a generally available solvent-based product that contains polymers of silicon. The coating is described as a ‘liquid glass’, which is normally clear, but adding a black pigment aids heat exchange between the wheel and the tyre. While a similar effect could be achieved using paint, the added weight would negate some of the performance benefits, adding 50-100 g per wheel. On the other hand, the coating is said to add only about 5 g to the mass of an individual wheel, presenting a negligible weight penalty. This is because, when applied, it is only a few microns thick (and also has a very high surface hardness of around 9 H).

The coating also has secondary benefits relating to airflow within the rim, as its very smooth and glossy finish reputedly helps reduce turbulence. It is not just smooth coatings that are applied to wheels though, and there are a number of heat-resistant coatings available that can be applied with an extremely smooth finish for the same reasons. Another benefit of the high-gloss finish is that it makes the inside of the wheel rim less susceptible to the build-up of debris picked up as a result of brake wear and from the track surface.

Coatings are not the only trick that some teams have used in an effort to improve the thermal and aerodynamic performance of their wheels. In the past, great effort was put into creating carefully sculpted wheels that steered the air where it was most needed. Those days are long gone now though, and wheel design is tightly regulated. However, this has not stopped some teams working within the regulatory constraints to try to garner every last ounce of performance. For example, observers spotted at the end of the 2013 season that the Mercedes team’s wheels featured a ‘textured’ finish on the inner surfaces, while those of Red Bull sported a dimpled effect.

The purpose of such finishes could be twofold. First, the texture could help to reduce the boundary layer of air on the inside of the wheel rim as it rotates close to the brake cooling drum, thus helping to reduce drag in much the same way as dimples on a golf ball. Second, the finish presents a greater surface areas, which combined with a heat-absorbing coating would further increase heat transfer from the brakes into the tyre carcass.

It is steps such as these that highlight the extent of the detail engineering that goes into a modern Formula One machine, and the fact that for the top teams, no stone goes unturned in the quest for performance.

Written by Lawrence Butcher