replacing the entire bar. MacPherson struts The MacPherson strut is a common form of strut suspension. This was not the first attempt at strut suspension, but in MacPherson's original patent, the anti-roll bar forms an integral and essential part of the suspension, in addition to its usual function in controlling body roll. A strut suspension like MacPherson's requires a hinged lower member between the chassis and wheel hub to control the wheel position both inwards and outwards (controlling the track), and also forwards and backwards. This may be provided by a wishbone with a number of joints, or by using an additional radius rod. MacPherson's design replaced the wishbone with a simpler and cheaper track control arm, with a single inboard joint, to control the track. Forward and backward position was controlled through the anti-roll bar. Overall this required a simpler and cheaper set of suspension members than with wishbones, also allowing a reduction in unsprung weight. As the anti-roll bar is required to control wheel position, the bars of a MacPherson strut suspension may be connected through ball joints. However many later "MacPherson strut" suspensions have reverted to using wishbones rather than the simplified track control arm of the original design. Semi active anti-roll bars Various methods of decoupling the anti-roll bar have been proposed. The first production car to use an active anti-roll bar was the 1988 Mitsubishi Mirage Cyborg. The "Dual Mode Suspension" equipped with the 16-v turbo model has front active anti-roll bar that has a hydraulic actuator built in the anti-roll bar link. The actuator can be operated with a switch on the dash board, changing the effectiveness of the anti-roll bar between the sport mode and touring mode. The Jeep Wrangler (JK, JL) and Jeep Gladiator (JT) also have a switchable decoupler on Rubicon models, to increase wheel articulation for off-roading. Active systems The first car to use an active anti-roll bar in 1994 was the Citroën Xantia Activa, a medium-sized sedan sold in Europe. The SC.CAR (Systeme Citroën de Contrôle Actif du Roulis) system featured an anti-roll bar that could be stiffened under the command of the suspension ECU during hard cornering. The car rolled a maximum of 2 degrees. In 2001 the BMW 7 Series (E65) introduced Active Roll Stabilization (ARS) "active" anti-roll bars that can be proportionally controlled automatically by a suspension-control computer, reducing body lean in turns while improving rough-road