Bound and determined

Tried to pull the HL in the toy hauler & it was like 4 inches to wide. So got the idea to put car tires on the stock rims cause the outlaws stick out past the rims a few inches. I’m Thinkin this will be all I need to get it in. Now I do t know much about car tire size that’s for sure but what I would like it the tire to not be wider than the rim when aired up. What tire size would I need to accomplish that?