I have the stock 18" wheels with 225/45 front and 245/45 rear. I would like to keep the stock 18" x 8" but put as wide a tire as I can on the stock 18" x 8", will 265/45 on rear and move the current rear 245/45 to the front work?
Will the stock 18" wheels hold the 265's or will they ballon out

 

i saw that you posted this on FA also, i cant remember if i answered it there. but you can fit 275 45 on the rear of your 18s if you want, but they will bulge like a bama. i think the 265s will bulge a little less (maybe not at all) and the 255's are the biggest possible fit recommended for maintaining safety and performance. i dont think the rear 245s will look good on the front because they are 45. the front should be 40 to maintain a lower profile look and to keep the VDC happy.

also note that rack advertises a set of PSports in 245-4 Front and 265-40 Rear for the stock 18's. not sure why they would do this, but when i emailed them about it, they said they could not recommend anything other than OEM. safe liability free answer. if you go the 265's please post clear and close up pics. the lack of pics is the only thing keeping me from going to 265 instead of 255. i hope you do it!!!!

 

What is the largest tire you could fit on a 18 X 7 wheel?

 

I ran 255/45/18 on my rears without any problems. There is a little tire bulge but its not bad. They will definetely hold a 265 but it will bulge out. If you do want to go 245 front/265 rear you should use 40 series profile tires, its the closest to stock overall diameters.

 

If you go to toyo.com, click on "tires", click on "sports car", click on "Proxes T1-S", then click on "get the tech specs" it will take you to a lengthy table. At the bottom it tells you which size tires fit which size rims. The bold number is the optimal rim size for the associated tire size. The upper and lower range numbers are what you might be able to get away with, but are not recommended.

If I understand things correctly, tire manufacturers do not recommend that the consumer exceed a 245/45/18 on a 8.0" rim. That doesn't mean that you cannot do it, there will just be consequences like extra roll, accelerated tread wear, etc...