Swingarm - Swingarm Types

Swingarm Types

Swingarms have come in several forms:

Swinging fork - 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.

Cantilever - An extension of the swinging fork where a triangulated frame transfers swing arm movement to compress shock absorber/s generally mounted in front of the swingarm. The HRD-Vincent Motorcycle is a famous early form of this type of swingarm, though Matchless used it earlier and Yamaha subsequently. The Harley-Davidson Softail is another form of this swingarm though working in reverse with the shock absorbers being extended rather than compressed.

Parallelogram Suspension was first introduced commercially in 1985 on the Magni "Le Mans". Magni called the system Parallelogrammo. This new suspension system eliminated the torque reactions normally associated with shaft drive motorcycles and enabled the bike to perform similarly to a chain-drive unit. Similar systems have been developed by other manufacturers.

Paralever is BMW's version of the system. It allows the driveshaft to pivot along the same axis as the sprung rear frame due to the addition of second link between the rear drive and transmission. Paralever was originally introduced in 1988 R80GS and R100GS motorcycles and provides a reduction in the phenomenon known as "shaft jacking" where the rear of the motorcycle would lift skyward under certain riding conditions.

Moto Guzzi has introduced a variant of the system it named the Compact Reactive Drive Shaft system (patented and named Ca.R.C.). The main difference is that the driveshaft is free to float into its structure providing much softer feedback from transmission. Additionally, the upper arm of the Ca.R.C. is not part of the structure but just a guide to close the geometry of the suspension (it means that, differently from BMW version, the suspension will work also with a broken upper arm).

Drag racing motorcycles will often use longer swingarms to keep their center of gravity, i.e. the engine, as forward as possible to reduce the tendency to wheelie at the start.

A single-sided swingarm is a type of swingarm which lies along only one side of the rear wheel, allowing the rear wheel to be mounted like a car wheel (unlike the conventional motorcycle double-sided swingarm). Single-sided swingarm are traditionally found on small motorcycles and scooters, where a robust chain case doubles as the swingarm linking the engine and rear wheel. Single-sided swingarms need to be much stiffer than the double-sided versions to accommodate the extra torsional forces, and as a result they are usually heavier than double-sided arms. 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 a the exhaust pipe. Later in 1950, Moto Guzzi introduced the Galetto, 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 these swingarms, most notably the Massimo Tamburini-designed 916 series. While they abandoned this style for the 999, they returned to it for the 1098 superbike in 2007, and it survives in the current 1198. The Triumph Sprint ST also features single-sided swingarm.

The advantages of single-sided swingarms are (i) that it simplifies rear-wheel removal, which now involves merely undoing perhaps a single nut and then pulling the wheel off the axle shaft. Also, (ii) (on a non-shaft drive bike) a single-sided swingarm can enable the rear chain sprocket to be separate from the wheel itself. This feature allows a full-enclosed oil-bath final-drive chain, but whereas scooters have always used this advantage, large motorcycles rarely do, even though their chains would benefit from such protection. A further advantage (iii) is that a single-sided swingarm gives a fashionable "clean" appearance to the bike's rear.