what are the largest diameter and width wheels you can put on a third gen 7 without modifications?

 

Its a unique size...... 18xSearch

18x10 front and 18x10.5 rear. Offset and tire size play a part as well.

 

What do you consider "without modification"? If you mean just body then what Goodfella posted is exactly right. If you mean full stock body and suspension you are looking at about 18x9F and 18x10R

 

Just be careful of the offset with a lowered car on 18's. My old CYM had Racing Beat springs and Tokico's on 18x9's with 245/40 series tires and they rubbed the fender. Had to roll them, and even put in a spring block for while to keep it from rubbing. Offset plays a big part.

Jose