Each driver is limited to four sets of Intermediates and three sets of Wets, which must cover all practice sessions plus qualifying and the race. This is due to FIA Sporting Regulations and the rule existed before Pirelli joined F1 at the start of last season.
McLaren head Martin Whitmarsh is just one person pushing for greater numbers of Wet tires, despite Pirelli arguing that degradation levels are low. Notwithstanding this belief, Pirelli Motorsport Director Paul Hembery has offered to bring in more sets of Wets from Didcot, should all teams approve to a change in the regulation.
Charlie Whiting, FIA Race Director, has already backed the idea. This means that more tires could be brought, should every team be able to agree ahead of Saturday practice.