When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
then why do i have 275/40/17 M/T on the car right now
The 255/50/17 is the largest tire recommended for a 17 x 8 rim. You could probably fit a 305 if you wanted to but it is not recommended. You are putting alot of stress on the side wall of the tire because it has to compress to fit the smaller rim.
I have run tires over the recommended width on rims with drag radials without any problems as I am sure thousands of others have as well. But on a street driving where you have to turn alot, that extra force on the sidewall could cause you to break the bead or something. I also like to tear around on/off ramps and autocross every once in a while. For my own personal peace of mind, I like to stick within therecommended parameters.