of a shaft drive machine would induce the opposite, causing the seat (and rider) to rise upwards, a phenomenon known as "shaft-jacking". This anti-intuitive sensation can be disconcerting to riders, which parallelogram suspensions seek to neutralize. BMW introduced its Paralever system on its 1988 R80GS and R100GS motorcycles, which adds a second link between the rear drive and transmission to allow the driveshaft to pivot along the same axis as the sprung rear frame. Moto Guzzi patented its Compact Reactive Drive Shaft system (Ca.R.C.), where the driveshaft is free to float into its structure, providing much softer feedback from transmission. An upper arm serves as a guide to close the geometry of the suspension. Extended swingarms - are often used by drag racing motorcycles (called dragbikes) to keep their center of gravity as forward as possible, which reduces the tendency to wheelie at the start. Single-sided swingarm - a suspension lying along only one side of the rear wheel, allowing it to be mounted to a hub like a car wheel. Also found on scooters, where a robust chain case doubles as the swingarm linking the engine and rear wheel, single-sided swingarms need to be much stiffer and more heavily built than double-sided, to accommodate the extra torsional forces. Having a single mounting point guarantees proper wheel alignment. Single-sided swingarms date from at least the late 1940s. In 1948, the Imme R100 produced by Norbert Riedel of Germany had both a single-sided front wheel suspension as well as a single-sided rear swingarm that doubled as the exhaust pipe. In 1950 Moto Guzzi introduced the Galletto, a large-wheel step-through scooter. In 1980, BMW introduced its first single-sided swingarm on the R80G/S, the "Mono-lever", which was superseded by the "Para-lever" used currently. Honda currently features this style of swingarm on the Honda VFR. Ducati has created several models featuring single swingarms, most notably the Massimo Tamburini-designed 916 series. While Ducati abandoned this style for the 999, the company returned to it for the 1098 superbike in 2007, and it survives in the current Ducati 1199. The Triumph Sprint ST and Speed Triple also feature single-sided swingarms. Images Squat and Shaft-jacking "Squat" occurs because the top of the final drive chain run pulls the swingarm upwards; "Shaft-jacking" occurs because the shaft drive bevel gear tries to "climb up" the large bevel gear in the wheel hub, thereby pushing the swingarm downwards and away