MAW Solutions Ltd Hanworth TW4 5PY Phone: 01273 493343
FOURNALES SUSPENSION SA, based in the south of France near Toulouse, has been designing and manufacturing their oleopneumatic shock absorbers since 1978.
Company founder Jean-Pierre Fournales was initially a design engineer within the french aerospace industry, while in his spare time raced in international motocross events. Appointed technical adviser to Bultaco in the mid-1970s , he designed the first oleopneumatic shock-absorbing suspension, which was fitted to the winning and 2nd-placed bikes in the 1978 world trials championship.
With the aim of designing and making innovative, high performance and high quality shock absorbers, the business has expanded steadily since then. Fournales now manufacture a range of shocks for around 700 motorcycles and more than 50 scooters. In addition, they also make shocks for wide ranges of 4x4’s, quad bikes, light aircraft, mountain bikes, trucks, race cars, and specialised applications such as cable cars.
The range of motorcycle shocks includes four styles of twinshocks as well as monoshocks. Pictured is a Fournales classic twinshock on a Harley FXE.
How Do They Work?
All vehicle suspension units comprise two basic elements: something elastic which allows displacement of the weight it supports but tries to restore equilibrium (a leaf spring, torsion bar, or most commonly a coil spring) and a damper which controls and limits the movements of the spring. Although the two elements are straightforward, the way in which they are combined and controlled has given rise to many different shock absorbers over the years.
Fournales suspension units uniquely combine high pressure air springs with hydraulic (oil) damping - hence “oleopneumatic”. The two main benefits of the design compared with a standard coil-spring shock are illustrated left. At point A the suspension is in a steady state, with rider weight supported by spring. With a small increase in force, the Fournales unit allows a little more travel than the spring, giving a controlled and comfortable ride. As the bumps increase, the air spring firms up at a rising rate, so that by mid-travel the air spring is becoming firmer than the coil spring, allowing better rider control to be maintained. Towards the limit of travel, at point B, the coil spring can bottom out with jarring discomfort, risking a loss of control. The air spring simply gets harder and harder in a fully predictable way, and bottoming out is virtually impossible.
Another benefit of the oleopneumatic approach is that by varying the air pressure in the shock - simply by pumping it up - the whole stiffness curve rises. This is much more effective in matching shock absorber performance to the rider and/or passenger weight of a motorcycle than adjusting the preload on a spring, which has the effect of providing stiffer support under steady conditions , but does not change the spring rate as the shock’s travel is compressed in use.
Fournales shocks are manufactured to very high standards. Top quality materials are used, and the internal seals are rated to withstand 300 bar pressure (over 4000 psi), which is at least 10 times the working air pressure inside the shock. Consequently Fournales shocks are long-lived and reliable. And, when they do eventually start to tire, they are fully rebuildable.