i have hamman 18,s 8.5 pg2,s on my 97 540,, and my tread is wearing thin ,, i dont mind the pirelli p7000 that i was using,, but i want a thicker tire in the rear,, i am currently runnin 235 on all 4,s ,,, i was thinkin of 255,s on the rear,, too big or just right??? and comments??