There is no doubting that larger wheels can look pretty good but on the other hand, the larger the wheels and the tyres the heavier they are and thus the more effect they will have on performance. Tests show that as wheel/tyre combinations get bigger, acceleration and fuel economy suffer often quite dramatically with a 10 percent drop in fuel economy between using 15-inch rims and 19-inch rims. Formula 1 has used 13-inch rims for the last 20 years and this is now out of step with the industry which tend to use 15-inch rims with lower profile tyres. In theory this means that a tyre company has less scope to apply the technology learned in F1 to road car tyres. This is not strictly true but it is clear that if one can market tyres that are the same size as those used in F1 there are likely to be more sales. There was talk a year or so ago of Michelin coming into the sport but the French company said that it wanted to increase wheel rims to 18-inches after the first couple of years.
“The 13-inch tyre is no longer relevant to the everyday road user,” says Pirelli’s Paul Hembery. “While 18-inch tyres would be a big step for Formula 1, there are many other motorsport series that already use this size. So there’s scope to go even bigger than that in Formula 1 in years to come. In order to underline F1’s role as a test bed for future mobility solutions, we believe that it benefits everybody to have as close a link between road car tyres and competition tyres as possible. However, we’d like to emphasise that this move is not something that we are actively pushing for, as our role in Formula 1 is not to instigate changes. Instead, it’s to help teams and drivers make the most out of the equipment, regulations and resources they have at their disposal – whatever they decide that framework is going to be.”
Thus the Pirelli test of 18-inch tyres this week at Silverstone was an interesting experiment. The tyres were run by Charles Pic, with the Lotus.
“It was a very early evaluation test and the different tyres and wheels affect the aerodynamics of the car quite a lot, but you could certainly feel that the tyres felt different to those we’re used to on an F1 car,” he explained.”
The objective of the test was to give Pirelli some initial loading information as well as for everyone to see what the cars looked like in this configuration.
“The new tyres looked stunning fitted to the Lotus,” Hembery said. “These are just a prototype concept, but if the teams decided that they wanted us to proceed in this direction, we have the capability to carry on development in this area and come up with a production-ready version in a comparatively short space of time. We’ve heard a lot of opinions already and we look forward to canvassing other opinions in the coming weeks and months. Even though performance wasn’t by any means priority here, the new tyres still behaved exactly in line with our expectations, so we’re clearly potentially at the beginning of a huge development curve, with the wheel and tyre size rules having remained unaltered for many years.”
The key technical advantage of an 18-inch tyre is a stiffer sidewall that helps maintain the structural rigidity of the tyre and also makes it easier for the tyre to maintain a constant pressure – as there is less actual air inside the tyre.
The reality is that if the wheel size changed, the cars would need to be completely redesigned because of the impact of the tyres in the airflow around the cars. The cars are generally changed from year to year so this is not necessarily a problem but it will mean that the philosophy of design will change as engineers try to find the downforce that will be lost with such a change.
“They are more reactive and nervous and on top of that you lose a lot of aero,” Pic said. “It is not even like you are on the aero you use at Monza, it is even less. The combination means you are five or six seconds off the pace.”