why do the load carrying heavy vehicle have large number of wheels
Answers
There are generally two reasons. The weight that each factor carries will depend on the jurisdiction involved.
ONE; when more tires/ wheels are employed, each one can have a lower weight carrying rating, and the loss of one tire takes less carrying capacity away.
TWO; the more tires/ wheels/ axles we spread the load over, the less point loading damage to the roadway surface.
That is why some states will require extra axles on what would be a ten-wheeler (one steering axle with a single tire on each side, and two carrying axles with dual tires on each side. Therefore ten total tires/ wheels.
The same truck with the same chassis and load box may have one single steering axle, two dual drive axles, and three single carrying axles, putting sixteen tires on the roadway. Super dumps even have a deploy able “trailer axle that can be lowered to run several feet behind the truck, putting eighteen tires on the road when fully loaded.