ok so i need 2 new tyres for the back of the Z, ive had the Pirelli P Zero 255/35 R18 Y (94) on for 6 months and they are almost illigal already!! now ive been looking at replacing them with some Falken Ziex ZE-914 - 255/35 R18 W (90) has anyone had any experiance with these? would i have any issues with just changing the back ones as the fronts are ok but cant really afford another 2 Pirelli P Zero 255/35 R18 Y (94) at the moment!