Question

Why do trucks have 8 rather than 4 tyres

Answer 1

Pressure is inversly proportional to area, so the force acting on a smaller area exerts a larger pressure as compared to the pressure it exerts on a larger area
If the truck would have only four wheels, more pressure would be exerted on the wheels which may burst. More no. of wheels reduces the pressure on one wheel. The weight of the truck will be properly distributed on the wheels and the truck would move easily.