i will let some of you know, i race with Grub, and we had a great battle at the states this year. my tyres were 38 on inside and 40's on outside. same track, same race, i started my tyres at 64mm rear and 62 front. after 30 mins i didnt measure them, but i still had a heap of tyres left. Grub actually measured them later the next day, think i still had a 0.8mm split and left to right were same size, so i doubt its the track, its more like Diff fluid weights. Grub has a set of my K Factory tyres to try out so he will soon see it may not be brand related either. good luck Grub. race ya soon