def not +18 i got 18x10 +18 on my car, the biggest i think ill fit under it is a 265, as the lip of the rim hangs out past the guard.
id say +22 or bigger, even +22 it would be close, on a 32R it would def need some guard work, you can fit 285s on a 10inch wheel no worries dont no about a 9inch but.