I just went up and measured one of mine on a 72" curve. Maximum is about 1 inch out for the outside edge of the oter rail, at three places: very near the front where the front ladder is at its lowest/fartherest out, the outer edge of the front of the cylinders, and at the rear there is some mechanism, pipe or something, that juts down from below the side of the cab. All three look like they jut justabout one inch past the outer rail: so,for example, if you are using Fastrack, none of them would jut out past the edge of the plastic roadbed, but they would come with 1/8 inch or so . . .