[Ether]

See Figure1 attached. In this Figure, the vehicle is accelerating just fast enough that the front wheels are about to lift off the floor. In other words, there is no normal force on the front wheels.

The force causing the acceleration of the vehicle is the (horizontal) friction reaction force Ma of the floor on the bottom of the rear wheels.

The weight Mg of the vehicle acts at the Center of Mass (CoM in the figure). The normal force on the rear wheels is Mg.

The torque around the CoM is zero, so Mah = Mgb => a/g = b/h.

If the acceleration is slightly increased, then a/g > b/h and the vehicle will rotate counter-clockwise and tip over backwards.