Plunger suspension on a 1953 BMW R51/3

A swingarm, or "swinging arm" (UK), originally known as a swing fork or pivoted fork, is a single or double sided mechanical device which attaches the rear wheel of a motorcycle to its body, allowing it to pivot vertically. The main component of the rear suspension of most modern motorbikes and ATVs, it holds the rear axle firmly, while pivoting to absorb bumps and suspension loads induced by the rider, acceleration, and braking.

Originally motorcycles had no rear suspension, as their frames were little more than stronger versions of the classic diamond frame of a bicycle. Many types of suspension were tried, including Indian's leaf spring suspended swingarm, and Matchless's cantilevered coiled-spring swingarm. Immediately before and after World War II, the plunger suspension, in which the axle moved up and down two vertical posts, became commonplace. In the latter, the movement in each direction was against coiled springs.

Some manufacturers, such as Greeves, used swingarm designs for the front forks, which were more robust than telescopic forks. In particular, sidecar motocross outfits frequently use swing arm front forks. The swingarm has also been used for the front suspension of scooters. In this case it aids in simplifying maintenance. In motorcycles with shaft drive, such as the Yamaha XJ650 Maxim, the shaft housing forms the left side swingarm.

Yamaha XJ650 Maxim has a driveshaft forming the left swingarm