SAKHIR, Bahrain - Pirelli's new 60% scale (height from rim to the tread 60% of width) wind-tunnel tyres could be to blame for some Formula 1 teams' troubles in 2013, according to a technical expert.McLaren faltered badly thrugh the northern winter in switching from the winning 2012 car to the new and uncompetitive MP4-28.THE PROBLEMIt's been a similar story at Williams and Sauber, which in 2012 were among the stand-out teams of the midfield and are now scrambling for pace in 2013.Referring to McLaren and Sauber, Swiss newspaper Blick's technical expert Mike Hammer said: "Both teams now believe they know where the problem lies. It has to do with the new Pirelli tyres. They are more angular than in 2012 and then deform differently in the corners, which has a great influence on aerodynamics."Millimetres play a role but the 60% tyre for the wind-tunnel models have led McLaren and Sauber astray.”An unnamed McLaren engineer agreed: "They (the Pirelli tyre models) are much worse than 2012."Faced with the latest criticism, Pirelli's motorsport director, Paul Hembery said: "We are talking about 11 teams with 11 different wind tunnels. It is not easy to build good 60% tyres.”The theory would explain why teams which made significant changes during the northern winter have suffered disproportionately so far tin 2013.