Final answer:
Tire chains should be placed on the drive tires to improve traction for effective downhill braking. This placement increases the grip and assists in maintaining control of the vehicle on slippery surfaces.
Step-by-step explanation:
Tire chains placed on the drive tires improve traction for downhill braking. The drive tires are responsible for propelling the vehicle forward, and when going downhill, they play a crucial role in maintaining control through braking. By attaching chains to the drive tires, you are effectively increasing the grip these tires have on surfaces that might be slippery due to ice, snow, or mud. This enhanced grip provided by the chains allows for more effective braking, which is especially important in heavy vehicles that have a lot of momentum going downhill.