Once you get into those larger vehicles, vehicle weight doesn't matter so much (for regulations and for road wear). What matters is axle weight, which stays fairly consistent as you increase overall vehicle weight. eg for delivering bulk construction materials, dump trucks have either one, two, or three load axles (along with the steering axle, which is calculated separately), and the load it can carry scales pretty closely with that (gross around 10t per axle (22k lbs), net around 7t per load axle). Anything over the standard limit pays significant fees for a permit (at least where I am)