A vehicle’s suspension and steering systems are critical in making sure that the car handles well and grips the road in all situations. Any worn or broken component will affect the way the car performs and can be extremely dangerous. For this reason all steering and suspension components need to be test regularly, so that any wear can be detected and rectified early.
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These systems have probably changed and developed over the years more than any other system found on the car today. The earliest cars were fitted with solid axles that transversed the car both at the front and rear, with the front wheels fitted to hubs that were connected with a pivot pin (kingpin). The hubs were then connected together with another rod that was connected to a tiller, similar to that found connected to a rudder on a rowboat. Moving the tiller left or right then steered the car. This was then all mounted to the car via a single leaf spring running across the car and mounted to each axle. Tyres were made of solid rubber and fitted to wooden spoke wheels. At speeds of 6-10kph this almost worked with only some effectiveness, so new systems were very quickly developed.
Now days all front suspension and most rear suspension is what is known as independent, meaning that each wheel can move up or down without effecting any of the other wheels. It is only when a solid beam or differential housing is used that the rear system will see movement on one wheel having an effect on the opposite side of the same axle. Many designs have followed, most of which are still used in some format to this day. Many of these types of suspension setups, are very much suited to certain applications rather than general purpose. Others have been designed more with cost and ease of production in mind, but they all contain the same basic components in some form or other. All systems have suspension arms, springs, shock absorbers, pivots & pivot mounts, steering rack or box and steering arms & joints.
Springs are generally manufactured out of very hard but flexible steel and may still be constructed by layering a number of curved narrow steel plates that are mounted to the chassis with pivots at each end and affixed the axle assembly in the middle, although this is usually only seen on commercial vehicles these days. Some of the components in suspension systems are technically misnamed, as the spring itself absorbs the shock produced as the wheels hit irregularities in the road surface, and the “shock absorbers” are actually dampeners to prevent the vehicle bouncing up and down like someone on a trampoline, every time a bump is encountered. The most common springs used though are constructed with steel rod that is wound into coils as we see in many other uses in everyday life. The wound springs found in suspensions on cars are a compression spring, meaning that in their relaxed state there are gaps between the coils that close up as weight or force is applied to the ends of the spring.
Coil springs work due to the twisting effect that the force applies to the steel rod. Some vehicles over the years have used a variance of this twisting style by using a straight bar that is mounted to the body so that the end of the spring cannot twist. The other end is then mounted to a suspension arm in a similar manner, so that as the arm moves up and down over bumps and holes in the road the bar twists to give the spring effect. This is called a torsion bar spring, requires less space within the wheel arch area, and is often used to allow lower body lines. A few vehicles have been manufactured over the years that haven’t used steel springs, and the most common alternative has been the use of compressed air within a rubber bag, similar to a heavy duty balloon. As the vehicle goes over bumps the weight compresses the air further, thus absorbing the shock.
Shock absorbers are usually a cylinder containing some oil that a shaft & piston slide in. As the piston slides up and down, it displaces the oil which is forced through restricted orifices and valves. This then slows the speed that the spring moves at thus reducing the bouncing. Most shockers today also have an area of compressed gas that assists in gentler reduction of movement from the spring. A shock absorber in good condition should only allow the car to bounce 1.5 times before settling at its normal ride height.
Ride height is the height that the vehicle sits above the road surface and by law in South Australia, no point of the “sprung” part of the car may be less than 100mm from the ground, measured on a flat surface, but each make and model does have a specified ride height that is used to meet their own requirements. This is usually measured as a distance from the centre of the wheel, to the lowest point of the wheel arch vertically above the centre of the wheel. This height should be maintained to keep the car handling within the parameters, that the manufacturer has spent much time and money developing. Many people tend to lower their vehicles, particularly to give it both a sportier look, & handling, but this will then require the vehicle to have the wheels realigned to slightly different specifications. It will also be likely to adversely affect tyre life. Generally a road car should only be lowered 25-35mm at the most, but even this will be outside the limits allowed by law.
There are many styles of mounting the body to the suspension system, but all independent suspension setups have one or more arms that pivot on their mountings at the body through bushes that have rubber or similar material to absorb some of the huge jarring stresses applied to them. The outer ends of these arms are then connected to the stub axle, that holds the hub, brakes, and wheels. Where the wheel is fixed as in most rear wheels, the stub axle is supported by more bushes similar to the inner ends of the arms, but when the wheel needs to pivot laterally to steer the car, a ball joint (similar to a hip or shoulder joint in our body) is used to allow movement in numerous planes.
As all of the components mentioned are constantly moving and subjected to extreme loads as they try to support and contain the weight and momentum of the car, they all will wear over time, and as this wear gets worse the car will not only feel “looser” on the road, its predictability and road holding ability will also deteriorate to unsafe levels. Many of these parts are very complicated and dangerous to replace or repair without the knowledge and special tools & equipment required, meaning that this work should only be carried out by qualified and experienced technicians. Any suspension work will also require the vehicle to be wheel aligned to ensure that the car drives and handles like it should and the tyres are protected from premature wear. Viva Auto Repairs can take care of all your suspension testing and repairs in one location, and will do a comprehensive check and report every time we service your car.