tire wheel help asap

Nope, the 255/40 is only 25" high and the 315 is near 25.7. I was just in this situation myself and had to go with 245-45-17 to match my 315-35-17. Look on nitto's site at their tire sizes, it shows the different sizes and their overall diameter. It will help steer you in the right direction.
 
jdetten said:
so would 245 45 17 fit on a 17x9.5 wheel

They fit but they look like a$$ IMO. 245 45 17, 275 40 17 and 315 35 17 are all the same hight. I had 245's on 9.5's but didn't like how it looked so I went with 275's. I liked the look but they would rub the swaybar and I didn't like the way the car drove (at least for me). One of my 17X9.5's was faulty so I got them to replace it with a 17X8 and they sold me another at cost ($200). So I went with the stock 245's up front. The car looks and drives great.
Scott
P.S. Sent you a PM