The Coaster Train
The modern Roller Coaster train is designed around wheel assemblies that do not differ much from ride to ride, or from manufacturer to manufacturer.
In the olden days, roller coasters used to slide on sheets of ice. Things have progressed a bit since then.
The early roller coaster trains featured running wheels and side-friction wheels. These side-friction roller coasters allowed corners to be taken. Whilst these coasters featured dips and climbs, they were never very steep, as the train was not fixed down to the track.
It was John Allen who invented the up-stop wheel, which was (and still is) the key to making roller coasters safe. The up-stop wheel meant that the train could not leave the track, and paved the way for steeper hills and, of course, inversions.
This diagram illustrates the modern wheel assembly
Article: http://www.coasterforce.com/coasters/te ... ter-trains