Tech Analysis: 18-inch prototype tyres

Tech Analysis: 18-inch prototype tyres

At the final day of the Silverstone test Lotus gave Pirelli’s prototype 18-inch a tentative 14-lap run, but just what do the changes mean for F1 and what is the purpose of the potential new tyre from as early as 2016 onwards? Will Tyson explains.

The Lotus team F1 car in the pit lane

Let’s start with a few buzzwords from the F1 2014: technology transfer to future road cars. The emphasis on turbo-charged hybrid power and utilising recoverable energy systems is a bid to make efficient road cars more aware to the public and bring new markets to F1, and so far this appears to be working. There is a vast amount of technology in F1 being transferred into the roadcars of today and indeed of the future and it is for this reason that Pirelli want to get in on the act.

Pirelli claim that a low profile tyre will be more relevant to their road car tyre development process. Quite how this works is, personally, completely beyond me as F1 cars have slick tyres that are specifically designed for racing. Do you see road cars with slick tyres? No. Semi-slicks? Yes, but they’re more like track-day cars. I do not see Pirelli’s point but let’s cut to the chase.

What we saw today was at least a five second laptime deficit with the new tyre and one unhappy driver who described them as a “big challenge”.

An 18 inch diameter tyre was suggested by Pirelli as a good platform. Currently the cars have a complete diameter of wheel and tyre occupying no more than 660mm on dry tyres (670mm on wets). The tyres run on 13 inch rims so the tyre width lies at roughly 165mm. The new prototype tyre has a width of just over 100mm, so that’s effectively 65mm in suspension travel lost from the tyre.

The tyre sidewall accounts for about half of an F1 car’s suspension. The front bulkhead and gearbox case is just about big enough to squeeze in a set of dampers, rockers, anti-rollbar and a heave spring so there’s little room for additional suspension travel as the cars are so stiffly sprung due to the high aerodynamic loads. This means that at high speed, with the current technical regulations F1 cars are on, the car will feel more nervous as it will not be able to take the extra load and the car will simply break traction.

I mention the current technical regulations because the tyres have a huge influence on the aerodynamic design. The large sidewalls and more rounded shoulders generate a wake that the teams have to manage, keeping it away from areas such as the leading edge of the floor, sidepod undercut and diffuser by using various techniques (Y250 vortex, sidepod vanes, floor cutouts etc.). Introducing the new tyre to the current aerodynamic package is far from ideal as all the aero devices interact with the larger diameter tyre. This means, at a track like Silverstone where the aerodynamics are critical to a car’s performance, the effect of a car not designed around a larger diamter wheel is amplified. Put it this way – it is like driving the car (800+bhp turbo with a ludicrous amount of torque) with a low-drag GP2 downforce setup.

The Lotus team F1 car on 18 inch tyres drives out of the garage

At lower speeds, providing the circuit is not too bumpy, the prototypes should have been OK as the contact patch is still the same. The problem is that even low speed corners are in excess of 50-60mph on average, so it is unfair to do a laptime comparison on a current car. The way the heat is generated within the core of the tyre is also a question mark and one that needs to be looked into. The brakes are so far away from the inside of the rim that their temperature will not greatly effect the warmup of the tyre, plus there is less volume within the tyre for heat to dissipate through anyway.

The only way Pirelli are really going to see if the tyres are worth pursuing is to convince the teams of the positive implications of running something closer to “road specification” and push for a change in the technical regulations which allow the aerodynamicists to have a proper re-think. Who knows, it may drag Newey back out from his virtual retirement?

Images courtesy of Lotus F1 Team