Alright so I got a flat tire yesterday (popped - looks like something stabbed my tire).
Luckily I came out to the car and started to back up, but heard rubber which was strange and looked to find my tire as flat as can be.

So I'm running 255/35/18 right now with the stock wheels being the 18x8.5 in the rear. I"m going to get two new rears, but I need some advice.

I've done the research that shows I should be able to run 235/40/18 just fine with a slight increase in sidewall and maybe a bit of a stretch. I know DW is running or used to run 235/40/18 on 18x8 (stalker status?). Anyways the guys at America's Tire said it would stretch and be lower sidewall, but not sure that is true. I'm not concerned about curb rash because I'm careful enough to not grind my wheels on the curbs so is there any other issues with running this tire size on the stock 18x8.5?

Main reason is price and getting more of a square setup in the future when I replace the fronts. I'm not even sure this makes sense considering I'm still running the 18x8 front and 18x8.5 rear.

Thanks.