Has anybody tried squeezing 275/40R18's on the rear?
I know they'll fit the 9" rims but would they foul the body?

TIA

 

ive been thinking the same, they will fit in the arch no problem

 

This chart should help just plug in sizes and it gives you the O.D. and the tire width
Tire Size Calculator - Tire Size Chart
Hope this helps

 

Well I can confirm they fit fine, no rubbing or untoward effects, so far

They look right for the car and it feels to have far better grip, although its hard to tell if this is due to new rubber or the wider contact patch.