Tyres
Over the past two seasons, tyres have been in the Formula One spotlight more than ever. Unlike previous seasons, tyre development has been driven by the need for a sporting spectacle rather than ultimate performance.
This has placed both Pirelli and the teams in an unusual position. Pirelli has had to build a less than optimal tyre, one that will degrade at a set rate on all the different track surfaces, while the teams have had to try to gain an understanding of the tyre’s characteristics and strike a balance between outright pace and tyre preservation.
As was highlighted at the 2013 British GP, this balance is not always reached, with the teams’ efforts to extract every iota of performance from the tyre package ultimately leading to catastrophic failures. In this case, some teams were running the tyre outside its recommended operating parameters to exploit a performance gain, at the cost of reliability (and safety).
The key reason behind these failures appears to be the fact that the Pirelli tyres are ‘sided’, due to the inner reinforcements being laid up in such a way as to perform optimally when fitted on a particular side of the car. Teams had discovered that sometimes it was preferable to run tyres on the ‘wrong’ side, presumably because this changed the tyres’ behaviour in one manner or another. Unfortunately this meant that when subject to a specific set of operating conditions – no doubt contributed to by the teams running more camber and lower pressures than Pirelli recommended – the rear left tyre failed spectacularly.
As a result of these failures the FIA has now regulated against such practice to prevent further problems. This will see teams having to stick within Pirelli’s recommendations for camber and caster settings, and run the tyres on the intended sides. Also, Pirelli is introducing a revised tyre construction, with a Kevlar rather than steel belt in the tyre’s structure. The result of these revisions should prevent further problems but will lead to a renewed race among teams to master the revised specifications.
Teams understandably want to gather as much information about the tyres they are using under both race and test condition from which they can draw conclusions about tyre performance and degradation. The two key areas which can be measured are tyre temperatures and pressures.
In the past, tyre temperatures could only be measured when a car was in the pit lane, using a pressure gauge and a thermal probe. Miniaturisation of infrared-sensing technology, however, has allowed tyre temperature measuring equipment to be incorporated into a car’s sensor package, providing real-time information on tyre condition.
There are three key methods for measuring tyre temperature – external infrared (IR) sensors mounted close to the tyre, infrared cameras and measuring devices incorporated into the wheel to measure carcass temperature. Initially, ‘single-channel’ IR sensors were used to measure the external temperature of a tyre, but they could only monitor a narrow strip of the tyre surface, so an overall picture of tyre temperature could not be gained. This disadvantage has now been overcome with the development of multi-channel IR sensors that can measure up to eight sections of tyre, all packaged in a unit weighing about 15 g. Versions of these sensors have also been mounted within the wheel rim itself, with a wireless connection sending the signals to a receiver unit. A glance at the rear floor of many cars in the Formula One paddock will reveal an array of miniature IR sensors pointing at the rear wheels.
IR cameras tend to be used only during testing sessions, because they are relatively bulky items and thus difficult to package effectively. Their main advantage is that they provide a complete overview of tyre temperature distribution, and can be used to assess factors such as heat soak from the brake rotors.
Monitoring tyre pressure is of equal importance to temperature readings. Pressure is dynamic and increases as the gas in the tyre heats up and expands, and it is vital to track the tyre’s operating pressures to ensure it is optimal. Wireless tyre-pressure monitoring systems are now the norm in Formula One, and consist of a sensor unit mounted on the tyre valve stem and a receiver unit in the main control electronics system.
As with temperatures, tyre pressures would in the past have been checked in the pit lane, but they varied from on-track pressures as the tyres cooled coming into the pits; now though, pressures can be logged dynamically as a race progresses. Some of the latest systems even combine pressure and temperature measurement in a single unit using a shared ECU, providing an integrated and therefore more compact solution.
Even with such comprehensive monitoring, Silverstone showed that teams can still be caught out by the unpredictable nature of the Pirelli rubber. It was for this reason that several teams protested against changes to the tyres earlier in the 2013 season, as they felt they had a better grasp than the opposition of the rubber’s foibles. Rest assured though that, with the introduction of a revised tyre construction – and tighter controls on how the tyres are used – engineers will be wanting to gather more data than ever on their racecars’ humble rubber boots.
Written by Lawrence Butcher