Running wheels guide the coaster on the track. Friction wheels control lateral motion (movement to either side of the track). A final set of wheels keeps the coaster on the track even if it's inverted. Compressed air brakes stop the car as the ride ends.

A roller coaster stays on its track through a sophisticated "three-wheel" engineering system that "hugs" the rail from three different angles. 1. Road Wheels (Running Wheels): These sit on top of the track and carry the weight of the train. 2. Guide Wheels (Side-Friction Wheels): These run along the inside or outside of the rail to prevent the train from shifting side-to-side during turns. 3. Upstop Wheels (Underfriction Wheels): These are the most critical for safety; they run along the bottom of the rail, effectively "locking" the car to the track so it cannot lift off during airtime hills or while going upside down in a loop. Modern steel coasters often use tubular steel rails that allow the wheels to wrap almost entirely around the track. This, combined with centripetal force—which pushes the car into the center of a curve—and the sheer weight/inertia of the train, ensures that the coaster remains securely attached even during the most extreme maneuvers and high-G inversions.