A 4th Dimension Roller Coaster is a type of steel roller coaster whereby riders are rotated independently of the orientation of the track, generally about a horizontal axis that is perpendicular to the track. The cars do not necessarily need to be fixed to an angle.
John F. Mares, a corporate attorney, invented the 4th Dimension roller coaster concept in 1995 and holds six US patents related to the technology of their spinning seat systems: US Patent #'s 5,791,254, 6,098,549, 6,227,121, 6,386,115, 6,477,961 & 6,606,953. The first 4th Dimension roller coaster to be built, X2, which opened at Six Flags Magic Mountain, United States in 2002, was designed and patented by Alan Schilke. In 2007, Intamin launched a variation of the 4th Dimension roller coaster under the name ZacSpin.On 7 July 2014, a teenager was killed after his harness sprung open during his ride on Inferno, a ZacSpin coaster at Terra Mítica in Benidorm, Spain. All other ZacSpins across the world ceased operations after the incident but have since reopened.
Arrow Dynamics was the first company to produce a 4th dimension roller coaster, lending its name to the ride style. The trains feature seats capable of rotating forward or backward, 360 degrees in a controlled spin. This is achieved by having four rails on the track; two acting as per normal, and two to control the spin of the seats. The two rails that control the spin of the seats, known as "X Rails", vary in height relative to the track, and spin the train using a rack and pinion gear mechanism.
The first installation, X², was a prototype and cost Arrow Dynamics and Six Flags itself a lot of money due to technical difficulties and design flaws. In 2002, the park sued Arrow Dynamics, which went into bankruptcy. Since then Arrow was bought out by S&S Worldwide and became the company's steel coaster division, S&S Arrow. In 2006, a second installation opened at Fuji-Q Highland in Fujiyoshida, Yamanashi Japan under the name Eejanaika. A third installation opened in 2012 at China Dinosaurs Park in China under the name Dinoconda.
In late 2012, S&S Worldwide unveiled a new concept which features a similar ride experience without the additional rail. A system of magnets would control the individual seat inversions. The first installation of a 4D Free Spin was Batman: The Ride at Six Flags Fiesta Texas in 2015.
The Intamin ZacSpin was developed in response to the Arrow Dynamics 4th dimension roller coaster. Some of the main differences between the Intamin and Arrow Dynamics/S&S Worldwide versions are the uncontrolled rotation of the seats, which produces a different ride each time, and single cars. Another notable difference is the absence of any lateral movements, causing some enthusiasts to not consider the rides 4th dimension roller coasters due to the fact that all movement is restricted to a 2 dimensional plane.
Kirnu at Linnanmäki in Helsinki, Finland, opened for the 2007 season and was the first of its kind. Later that year Inferno opened at Terra Mitica in Spain with an identical compact layout. In 2009, Insane opened at Gröna Lund with a different track layout. In 2011, the first ZacSpin in the United States opened at Six Flags Magic Mountain as Green Lantern: First Flight, and is themed to the DC Comics superhero of the same name. It features the same layout as Insane.
There is considerable debate within the roller coaster community as to whether or not the spinning of these coasters qualifies as an inversion for the purpose of records. Guinness World Records gave Eejanaika the record with 14 inversions. However, other more coaster-specific record bodies such as the Roller Coaster Database do not recognize this claim and instead count only track inversions, which gives the record of 14 to The Smiler.