Why the forklift truck is rear wheel drive and why the forklift tires at the back is smaller than the front tire?

Because when you lift loads the load on the front tire so payment must be in the front tire and be larger in size

While travellinng with heavy load, most of the load will be acting on front wheels, and also easier to handle the equipment with rear wheel steering.

The forklift truck is not a rear wheel drive .

The rear tires is smaller than the front to give the driver ability to Movement and maneuver