A swingarm is the main component of the rear suspension of most motorcycles and ATVs. It is used to hold the rear axle firmly while pivoting vertically to allow the suspension to absorb bumps in the road.
Swingarms have come in several forms over the years:
Twin-shock - the original version consisting of a pair of parallel pipes holding the rear axle at one end and pivoting at the other. A pair of shock absorbers are mounted just before the rear axle and attached to the frame below the seat rail.
Monoshock - came about in the mid-eighties and utilized a single shock mounted behind or under the engine and linked to the swingarm with additional pivots. This arrangement allowed for greater suspension travel and eliminates the need to synchronize shock absorbers.
Single-sided swingarms allow the rear wheel to be mounted like those of an automobile. This makes wheel maintenance simpler since removal involves the loosening of a single nut, sliding the wheel forward to slacken and uncouple the drivechain, and then pulling out the axle shaft. With their S-shaped contour, these swingarms need to be much stiffer than the double-sided versions to accommodate the new torsional forces incurred by holding onto the wheel by just one side. Having a single mounting point also guarantees proper wheel alignment.
Ducati has created several models featuring these swingarms but have chosen to return to double-sided versions for their most recent models. BMW has long been an advocate and even incorporates shaft-drives within them to eliminate chain maintenance.
The quest for additional performance through weight reduction has seen the departure of the center stand that can be used to raise the rear wheel off the ground. Lacking this built-in facility, quick rear wheel removal becomes moot without a wheel stand.