Tried to search for it, came up empty. On another forum someone was talking about 255 being the widest you can squeeze on a stock 18x8, is there any truth to this? What is the widest possible rubber to get on there?

 

You could squeeze wider than 255's on a 8" wide wheel but 255 is the widest section width recommended.

 

So I guess the question I really should be asking is, what can I get away with, ignoring manufacturer or retailer recommendations, and at what point it could actually be dangerous or hamper performance?

 

Anything larger than a 255 width will start to bulge the sidewall. You will get a loss in handling performance. I have seen a lot of people mount 275 tires on an 8" wheel. Technically, it can be done... it's just not recommended... Plus IMHO it looks terrible.

 

you will have to also take into consideration the sidewall height

after extensive research on this on my 18x8 rims i went with 255/45/18s

they were the closest rolling diameter to stock

here is a handy calculator

http://www.1010tires.com/tiresizecalculator.asp

 

probably not a good idea; the manufacturers engineers usually know what is acceptable for performance and/or safety, if they could recommend a wider range of wheel widths, they would do it because that would allow them to sell more tires . . . I would go with the real engineers recommendations over the "Internet forum engineers" every time

 

Now that's funny