I borrowed Fan2488's wheels

275 will begin to bulge on an 8 inch rim. With a 35 or smaller ratio, it could have traction/tire wear issues. I wouldn't go much higher than a 245 or 255 on an 8 inch rim. That will still bulge out some. As you can see in the pictures scoop posted, a 225 tire fits the 8" rim pretty well.

If it was a 16 or a 15 inch wheel, a 275 tire would have more side wall allowing for more bulge without affecting the contact patch negatively.

 

Thanks for the info

What about a 9" wheel? since im planning to run the Cobra R's which are 9 inches wide. Is there any problem using 275/40s on those?

 

A 275 tread width is 10.8" (give or take based on the tire manufacturer) so you'll be much better on a 9" wheel than an 8".

I believe that 275/40 was stock on the cobra. Should be good to go. Always consult the tire manufacturer (not the retailer) to be sure though.

 

275/40 will go on a 9 with no problem. I have 295/35 on a 10 and it fits perfect so i think 275/40 on a 10 would not be wide enough.

 

Yeah, a 275 on a 10" rim would run the risk of breaking the bead if you leaned on it too hard.