pls ansurgently , tractors have large tyres , bulldozers have caterpillartracks and heavy buses / trucks have eight rear wheels . give one reason common to all these ?

neede today urgently

All these trucks have large wheels because if they have small wheels they apply a greater pressure on the earth.When going on a Kuccha road , This can affect them in rainy season as their tyres will do deep inside the puddle formed by the rains . So all heavy trucks have large wheels so that they apply a lesser pressure on the earth.