The increase in engine performance with each new model launch means that suspension systems are becoming more and more critical.
The chassis and especially the springs and shock absorbers provide the link between the wheels and the body and ensure optimum contact with the road.
One of the most popular upgrades to a bakkie or overlander these days is a set of fancy shocks. Whether you want to improve your vehicle for towing, carrying load or being a more capable off-road performer a set of upgraded shocks can be tailored to those needs. The companies selling these components like to use a variety of terminology, but what does it all mean?
Bump steer is when your wheels steer themselves without input from the steering wheel. It is when the front or rear wheels begin to toe-in or toe-out during vertical suspension movements caused by undulations.
The spring rate is the amount of force needed to deflect a spring a given amount and is usually measured in pounds per inch of deflection. This rating is determined by the diameter of the spring and the length or number of coils. The spring rate is a compromise between having a soft enough spring to allow the suspension to handle the undulations while being stiff enough to keep the car from bottoming out when hitting a bump. The spring rate will need to be tailored on the amount of weight that you are planning to carry on the vehicle.
The job of the anti roll bar is to resist the vehicle’s tendency to lean during cornering. Anti roll bars are useful in suspension tuning as you can make adjustments to front and rear anti-roll bars independently without affecting other settings. A stiffer anti roll bar will reduce body roll while a softer setting will increase body roll.
The shock absorber slows down and controls the oscillations of the spring as it absorbs imperfections in the road surface. Basically, the shock dampens the movement of the springs. It does this by converting kinetic energy into thermal energy through fluid friction. This involves the flow of oil being slowed down by valve passages inside the damper.
Dampers work in both directions, the compression stroke, which is called bump, and the extension stroke, which is called rebound.
During bump, the dampers and springs absorb the upward movement from cornering or road irregularities. If there is not enough damping then the cycle begins again until the car returns to the original ride height, with a bouncing motion. It is important to have enough bump stiffness to be able to deal with uneven surfaces. However, if there is too much damping, it is like running no suspension and any upward motion will be transmitted directly to the chassis.
During rebound the dampers extend back to their original position using the stored energy from the springs. Generally the rebound stiffness needs to be set higher than the bump setting to cope with the stored energy being released. If the damping on the rebound is not effective, the wheel will quickly return through the static level and start to bump again, with the bouncing effect unsettling the suspension with little control. If there is too much rebound stiffness the wheel could hold longer in the wheel arch than needed, losing contact with the road as the forced required to push the wheel back down are not quick enough to respond to the changing surface levels.
Certain dampers, especially those at the higher end of the market allow for adjustability of the rebound and compression (bump) and you can fine tune your setting in that way. Most high quality items specifically developed for each models and will have a good base setting right out of the box.
Text: Reuben van Niekerk