Twinshock refers to motorcycles that have two shock absorbers. Generally, this term is used to denote a particular era of motorcycles, and is most frequently used when describing off-road motorcycles.
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 the 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. Motorcycles with only one shock absorber are called monoshock motorcycles. The performance of monoshock motorcycles was vastly superior to twin shock motorcycles. Accordingly, this design distinction is readily used to categorize motorcycles. Since monoshock motorcycles have been the norm since the 1980s, 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.
It is important on twin-shock motorcycles that both shocks be the same, and that if they are adjustable, that the adjustments on both sides be the same. Otherwise, there can be a torque to the swingarm which may cause dangerous handling and braking characteristics.