There are at least two fellas I know that are also running "275/40s" on all four corners that haven't encountered any issues whatsoever. That's probably about as far as you'd want to go on an 8-inch rim, however.I've got 275/40's all the way around on mine with no issues
I'm getting rear tires soon and think I'll go with the 255'sI should also add that the 255/45s are a little taller than the stock 245/45s. This calculator is helpful: https://www.1010tires.com/Tools/Tire-Size-Calculator. This is why some have gone 255/45s all around (and allows for full rotations).
How do you explain that some have stated they have over 40k miles on the the car with 275/40s in the rear, or in some cases all around? If a tire lasts that long then it must wearing just fine. I understand what your saying thought. All shops I talked to said it would work but that would be the limit. They said the side wall would budge and you may not like the look, I already know I LOVE the look. Heck, if they made a 265/40 20" wheel I'd go with that to be safe. 255 is not much different than 245.You can squeeze a 275 tire on an 8 inch rim but it will not perform or wear properly. A rim that is too narrow will pinch the tire in and cause it to balloon more in cross-section. Look at the the attached diagram for tire fit issues.
I think there was some confusion, some say the chrome clads are 9" wheels other say 8". May I ask how long you've had the 275 on the back and did you notice any change in side to side movement or handling? And yeah that extra grip must be nice! I wish they made a 265.... I may go 255 all around to be "safe" but I really want to keep my rims and get the 275s.I had 275/40/20 mounted on the back on my stock chrome clads no problem. My car is also lowered 1.7". Firestone store did it no questions asked. Looks and rides fine. Firestone gave me a 40k tread life warranty on them. Straight line traction is significantly better than the 245s!