How does adding weight to the back of a pickup increase the friction between the tires and the icy road?

Question

Quizplus · Accepted Answer

Adding weight to the back of a pickup increases the normal force (R) between the tires and the road, which in turn increases the frictional force because friction is proportional to the normal force. The symbols μ and friction coefficients remain unchanged; it's the increase in normal force that enhances friction.

How Does Adding Weight to the Back of a Pickup