Pirelli already testing 18 inch tyres for F1
Pirelli and Michelin testing new 18 inch tyres
Although that it is well known that Michelin is fond of introducing 18-inch wheels onto the F1 racing scene, then Pirelli was the first tyre company to make and introduce its brand new 18 inch F1 tyres.At the time, 18-inch wheel and tyre units were only used on regular passenger cars.
Pirelli Tests New 18-Inch Wheels combined with Lotus to fit the 18-inch wheels and tyres on to the Team’s E22 Chassis and the new tyres were tested on the Silverstone race track.
More reading http://www.wintertyres-yorkshire.co.uk/pirelli-tests-new-18-inch-wheels/