Braking has the opposite effect to acceleration, increasing the reaction force at the front and reducing that at the back. We may generate braking force at both wheels. This leads to replace by in eqns 13 and 14.
Figure 7 (lower panel) illustrates how the weight is transfered at the braking force is increased. This time the braking force is limited either by the front wheels losing traction, or by the rear wheels lifting off the ground. If the front and rear wheels contributed to the braking force equally, we would be limited by the point at which the rear wheels lost traction. We need to limit the braking force at the rear wheels so that it is less than that applied at the front.