Monoshock

Twin shock absorbers

During the late 1970s and 1980s, motorcycle rear suspension design and performance underwent tremendous advances. The primary goal and result of these advances were increased rear wheel travel, as measured in how far the rear wheel could move up and down. Before this period of intense focus on rear suspension performance, most off-road motorcycles had rear wheel travel of about 3.5–4 inch (9–10 cm). At the end of this period, most of these motorcycles had rear wheel travel of approximately 12 inch (30 cm). At the beginning of this period, various rear suspension designs were used to reach this degree of performance. However, by the end of this period, a design consisting of using only one shock absorber (instead of two) was universally accepted and used. The performance of single shock absorber suspensions was vastly superior to twin shock motorcycles. Accordingly, this design distinction is readily used to categorize motorcycles. With the exception of Bentley and Draper system (New Imperial and Brough Superior machines) and the HRD (later Vincent) system both developed and patented in the 1920s it is only since the 1980s that monoshock motorcycles have been the norm, the term "twinshock" is now used to categorize vintage motorcycles. This distinction is important in that it provides classes used for vintage motorcycle competition. For example, vintage motocross races are held for older motocross motorcycles. To prevent the better-performing monoshock motorcycles from dominating the competition, there are separate competition classes for monoshock and twinshock motorcycles, which prevents them from competing directly against each other.