A side friction roller coaster is an early roller coaster design invented by Edward Joy Morris. The design introduced side-friction wheels to help prevent trains from derailing during curved portions of the track. In addition to weight-bearing wheels traditionally located on the underside of each train car, friction wheels were added to both sides, which roll perpendicular along the inner edge of the track.
The first side-friction coasters appeared in the late 19th century and were mild in comparison to modern-day roller coasters. They declined in popularity several decades later as newer coasters began incorporating a third set of underfriction wheels, which further improved safety and allowed for more thrilling track designs.