I've done this numerous times on musclecars. Take the width up one spec and the sidewall down one.
You're looking at 9 1/4" width on what you have and jumping to a 10" width on the 255's. It theoretically keeps the overall diameter of the tire the same. (sorry didn't stop to calculate that for ya, just assumed on the sidewall %). It will go, but your backspacing is the concern. It always works for muscle cars as we wanted to run wide in back and used spacers (common until the '80's, now we just buy wheels that fit). So measure how much space you have, you're running 3/4" over. divide that in half as obviously the outside and inside will have equal amounts of extra when the tire is mounted. so 3/8".
Do you have that much space on the inside? I'm not sure on my ex, never measured, but usually you will on the rear, check the shock's that's where the rub is. Then check the inside front of your tires for the same 3/8" clearance with the steering turned to the left and right. If you have all that then you're cool.
Now. If you don't want tire rub, then you're going to want to either have stiff as heck suspension, take off plastic, roll your fenders, or take corners and bumps slow like a lowrider.
Not to be racist at all but talk to mexicans. They really roll wheels deep with no tire rub. I'm not sure if most of them get their speedo's redone, but here in Kansas it's pretty serious and they love to talk trucks on wide rims.
