Ever wonder why trains have steel wheels instead of rubber tires?
It’s to reduce rolling friction. When your car is driving on the freeway, something like 25 percent of the engine’s power is being used to push the tires down the road. Tires bend and deform a lot as they roll, which uses a lot of energy.
The amount of energy used by the tires is proportional to the weight that is on them. Since a car is relatively light, this amount of energy is acceptable (you can buy low rolling-resistance tires for your car if you want to save a little gas).
Since a train weighs thousands of times more than a car, the rolling resistance is a huge factor in determining how much force it takes to pull the train. The steel wheels on the train ride on a tiny contact patch — the contact area between each wheel and the track is about the size of a dime.
The downside of using steel wheels is that they don’t have much traction — which is why trains literally spray sand on the tracks just in front of the steel wheels.