Go to any power wheelchair manufacturer’s website and you will see information about suspension. Spend some time reading clinical papers or attending seminars and you will inevitably hear about suspension, whether the information is fact-based or simply relayed in fanciful buzz words. But what is suspension? Why does it matter? Suspension is an important aspect of a power wheelchair and plays a factor in selecting the appropriate power base for a client.
Vehicle suspension is the mechanical system of springs, shock absorbers, and linkages that connect the wheels to the chassis. The suspension in a power wheelchair is made up of multiple parts, most visibly the caster arms and springs. Suspension is important to user comfort, user safety, drivability, obstacle climbing, and durability of the power chair.
Experiencing high amounts of vibration in a power wheelchair has been linked to user fatigue and discomfort. Power chair manufacturers employ different types of suspension systems to reduce this exposure, mostly by utilizing a spring setup with linkages. Stiff springs provide stability, but ride quality can suffer because of their rigidity. Soft springs are more comfortable but can lead to instability and poor drivability. The geometry of the linkages is critical to prevent either extreme of instability or discomfort in order to reach a suitable ride quality, although it’s still not the most optimal solution.
So why isn’t a suspension of just springs optimal? The reason lies in the nature of a spring. Springs only store energy until it is released later. Consider a bow and arrow: when you pull back the string, energy is stored. And then when you release the string, it snaps back into place and vibrates. This return-to-position and uncontrolled oscillation are the inherent characteristics of a spring. Left unabated, a spring-only suspension will just keep bouncing!
How can the motion of the spring and suspension be controlled? The answer is the Shock Absorber – a hydraulic piston that damps the speed of oscillation. The shock does this by converting motion (kinetic energy) into heat, which dissipates. When a shock is used with a spring, the spring still absorbs the impact force, but the shock slows down its release, controlling the ride. So instead of a bumpy, swaying carriage ride, you get a smooth automotive feel.
Quantum recently partnered with an automotive shock manufacturer to develop a true shock absorber for use on power chairs, small enough to fit properly and designed for the weight and drive characteristics. The ride control provided by this shock allows for soft, comfortable springs without compromising stability or drivability. The shock is packaged neatly in a coil-over arrangement: the spring (or coil) is mounted over the shock absorber.
For maximum user comfort and safety, Quantum is proud to offer the Smooth Ride Suspension (SRS) – a coil-over suspension that comes standard on our Group 3 power chairs: the Edge 3 and 4Front®. You get an automotive-grade, oil-damped shock absorber and comfortable springs on your complex rehab power chair – no need to try to fund a Group 4 chair to receive best-in-class suspension. Quantum SRS – enjoy the ride!