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.

The earliest gravity railways in the United States were used primarily to transport coal down mountains, often to the nearest river or canal.^[1] The Mauch Chunk Railway (MCR) in eastern Pennsylvania was constructed in 1827 and was the second of its kind in the US.^[1] Before long, tourists attracted to the novelty of this technology were offered rides.^[1] Passengers enjoyed panoramic views along the descent, which started at a leisurely 5 mph (8.0 km/h) and reached speeds up to 65 mph (105 km/h).^[1] The MCR and similar attractions became widely known as scenic railways.^[2] The commercial success of these amusement rides inspired future advancements in what would eventually evolve into the modern-day roller coaster.^[1][3]

One passenger inspired by the MCR was inventor and businessman LaMarcus Adna Thompson,^[3] founder of the Eagle Knitting Company, a hosiery manufacturer.^[4] Building upon earlier ride patents for concepts never constructed, he developed his own patent called the Switchback Railway.^[3][5] The first installation opened as the Gravity Pleasure Switchback Railway at Coney Island in 1884.^[6]

In 1894, Edward Joy Morris took the concept one step further with the invention of side-friction wheels that were installed vertically on the sides of each train car, which were then seated in a trough configuration.^[6] Patented as the Figure Eight Toboggan Slide, the side-friction wheels made contact with the side rails, making derailment less likely.^[6]

Side-friction roller coasters could achieve greater speeds than the switchback design, especially around curves, which led to thrill-inducing lateral g-forces.^[6] The security of the updated design enabled roller coasters to operate without a brakeman, which were previously required to ride along and slow the train at various points along the track layout.^[6] Instead, ride operators working in the loading station only needed to rely on a hand-operated friction brake to stop the train when it returned.^[6]

Morris formed the Morris Chute Company, which manufactured carousels and roller coasters.^[6] More than 250 Figure Eight coasters, also called toboggans, were installed around the world.^[6] One of the well-known installations, Leap-The-Dips, opened in 1902 at Lakemont Park in Altoona, Pennsylvania.^[7][8] It is one of the last remaining side-friction coasters still in operation.^[8] In 1903, Morris sold the company, which reemerged in 1904 as the Philadelphia Toboggan Company.^[6] The invention of underfriction wheels, also called up-stop wheels, resulted in the demise of the side-friction configuration.^[2] Introduced in 1912 by John A. Miller, the newer design added a third set of wheels running beneath the track, further enhancing security from derailment, which paved the way for faster speeds, steeper drops, and new elements in track design such as the airtime hill.^[2][9]

• Leap the Dips at Lakemont Park in Altoona, Pennsylvania. Opened in 1902, Leap the Dips is the oldest roller coaster in the world and the last remaining side-friction roller coaster in North America. It was out of service from 1985 to 1999.^[10]
• Slope Shooter at the Higashiyama Zoo and Botanical Gardens, built in 1961. It has a long, winding layout, and has troughs made of steel and concrete.