[JVN]

A few other notes:
If you have multiple motors driving the same wheel... the load will be divided evenly among those motors.

If you have multiple wheels, the weight of the robot is spread over those wheels. The weight resting on each wheel will obviously determine the friction force between that wheel and the ground.

Multiple wheels connected to the same motor/gearbox will contribute their loads together.

Non driven wheels, contribute no load, but represent traction which isn't being used to help accelerate the robot, or push obstacles.

-John