Why do transport trucks sometimes have many spare tires hanging from their undercarriage, almost as many tires as those being used? Surely they don’t expect almost all tired being used to break down at once?

Question

Why do transport trucks sometimes have many spare tires hanging from their undercarriage, almost as many tires as those being used? Surely they don’t expect almost all tired being used to break down at once?

In: Engineering

Answer 1

Every tire a vehicle has on the road decreases its fuel efficiency and increases vehicle wear. Trucks can have an extra axle which is only lowered to the ground when the cargo is load is enough to exceed the rating of the other axles already on the ground. This axle is always raised unless needed.