The Suspension Revolution

Royal Enfield’s swinging arm rear suspension was revealed in 1948 on the prototype 350 Bullet trials. Its success in competitions ensured it was then used on road-going 350 Bullets and 500 Twins, making them the first full production motorcycles to feature this design anywhere in the world. Within a few years, virtually all manufacturers had adopted this Royal Enfield design and most still use it today.

From the first day an engine was clipped onto a bicycle and a brave Victorian gentleman wobbled down a road faster than his legs could possibly have pedalled, manufacturers struggled to provide riders with a motorcycle that’s both comfortable and handles well. The lack of damping on girder forks and shock absorption on a rigid frame was guaranteed to rattle bones and jiggle kidneys. All a rider had to isolate him from the vagaries of the road surface were a couple of small springs mounted below his saddle.

The motorcycle press began to feature articles on advancements in suspension in the late 1930s. Most early attempts were variations of a plunger arrangement, whereby the rear wheel spindle’s up and down movement was controlled by springs contained within damper units that formed part of the rigid frame. Experiments were also carried out on a cantilever design whereby an extension of a swinging fork compressed springs in front of the fork, usually underneath the saddle

Several manufacturers went into production with these two early forms of suspension immediately prior to World War Two and continued to use them once hostilities ceased and civilian motorcycle production recommenced. Other novel post war designs included swinging arms with complex and costly torsion bars and an enlarged rear wheel hub with springs inside it. This short-lived design also became one of the first motorcycle products to have a safety warning cast into its housing!

Through 1946 and 1947, Royal Enfield invested heavily in the development of a new type of sprung frame. Its design was patently different from all the others on the market. A casting formed the main pivoting lug with two phosphor bronze bushes for bearings lubricated by grease. Two telescopic legs attached to the rear of the swinging arm had an up-and-down movement of two inches that was damped by oil. These telescopic legs, or shock absorbers, were attached to the swinging arm and rigid parts of the frame by rubber bushes for additional damping. It was simple, pleasing on the eye and effective.

Enfield’s new suspension was not revealed to the public in the usual manner, which entailed producing beautiful road-ready machines then whipping the covers off them to a fanfare of trumpets at a prestigious motorcycle show. Instead, it entered three trials Bullets, including swinging arm prototype, GNP 770, ridden by Charlie Rogers, in the Colmore Cup trial of March 1948. This sensational showing caused a wave of speculation and debate amongst spectators and press alike.

Despite not winning the Colmore Cup, swinging arm Bullets continued to be entered in competitions throughout the following months. The British ISDT selection panel was so impressed that three 350 Bullets were included in the British team for that year’s competition in Italy. This proved to be hugely successful as Rogers and Vic Brittain both secured gold medals on their Bullets and Great Britain won the International Trophy..

Just a couple of months later, when that year’s biggest motorcycle show was held at London’s Earls Court, the road-going 350 Bullet and its new sister, the 500 Twin, sported swinging arm suspension. The goal of achieving superior comfort and handling, especially off road where rear wheel adhesion on all types of terrain is critical, had been achieved. The rest is history… within a few short years every other manufacturer had followed Royal Enfield’s lead and adopted swinging arm rear suspension. Most still use it to this day, as does Royal Enfield - just look at a 2021 Bullet or Classic and you will see exactly the same principles in action; even the components appear strikingly similar to those that first graced GNP 770 in March 1948.

Royal Enfield’s swinging arm suspension - a simple system that revolutionised motorcycle design and has transformed the ride experience of millions of motorcyclists for more than 70 years.