Ratings depend on the park.. IN SOME cases it has to do with the tightenss of the turns in the park.. For example Grand Canyon south rim I have driven through it with a car.. I'm kind of glad I was in a car and not my 38foot motor home cause I'd never have made the curves.
IN a COE park I spend some time at on occasion my 38' Rig will fit a 28 foot site, well SOME 28 foot sites. (I drive a class A). but the site length is 28 feet. if I park on one of the shorter sites I need a ladder to take down the ladder I need to take my Bicycle off the rack (Short and long ladders)
Good site for working under the rear overhang area on the MH though. Pull up a chair and have a seat and do the repair.
Other sites.. Well if there is a tree in the way I need 38 feet.
And if I want to park the car in front of the motor home 45 or more.