Car suspension system

When you think of the performance of a car, you generally think in terms of power, torque and acceleration figures. But all these figures would be useless, and uncontrollable, if not for an ‘out of sight and out of mind’, but crucial component — the suspension.

The job of the suspension is to maximise contact between the tyres and the road, to provide steering stability and keep the passengers comfortable.

There are three fundamental components of any suspension: springs, shock absorbers (or dampers) and anti-roll bars.

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SPRINGS

We’ve all experienced the way a spring works; it is elastic, and coiled up within it is a certain amount of energy that makes it extend and compress. The springs in a car’s suspension work on the same principle. When your car is on the road, it’s weight compresses the springs. So when the wheel encounters a dip in the road surface, the spring will extend and keep the wheel pressed down to the ground. Or if it hits a bump the spring will compress and again keep the wheel in contact with the road. There are three types of springs, coil springs, leaf springs and torsion bars.

Coil springs are the most common type and you will see them on most cars. Leaf springs are what you would find in older cars, and on trucks and heavy-duty vehicles today. The torsion bar is basically a length of metal rod anchored at one end to the car body, and at the other end to the suspension lower link. As the wheel passes over a bump the bar twists. It returns to its original position when the bump is passed and restores the car to its normal drive height.

While springs are essential for a car’s suspension system, they alone can’t provide a smooth ride. Why? Because while springs are good at absorbing energy, they are not so good at dissipating it. Therefore, you need dampers or shock absorbers to dissipate that energy. If you had springs without dampers, when you hit a bump, your car would continue to bounce until the energy dissipated.

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SHOCK ABSORBERS

So, how does a shock absorber work? A shock absorber is basically a fluid- or gas-filled reservoir within a tube that acts as a cushion between the road and car. It is usually placed between the frame of the car and the wheels. The upper mount of the shock absorber connects to the frame, while the lower mount connects to the axle, near the wheel. On the inside, the shock absorber’s upper mount is connected to a piston rod, which in turn is connected to a piston that sits in a tube filled with hydraulic fluid. When the car wheel encounters a bump on the road, causing the spring to coil and uncoil, the energy of the spring is transferred to the shock absorber through the upper mount, down through the piston rod and into the piston. As the piston moves, the oil is forced through tiny holes and valves into another chamber as it’s compressed. This flow resistance can be altered by changing the size of the hole, which is called damping rate. The wider the aperture, the lower the resistance or damping rate, which means a softer ride.

There are different types of shock absorbers like twin-tube, mono-tube, gas-filled and exterior reservoir but they work around the same principle.

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ANTI-ROLL BAR

Now let’s look at the third element of the suspension, the anti-roll bar. Its purpose is to keep the car’s body from rolling in corners. An anti-roll bar is a metal rod that spans the entire width of the axle and effectively connects the left and right sides of the suspension together. When the suspension at one wheel moves up and down, the anti-roll bar transfers movement to the other wheel. This creates a more level ride and reduces the car’s propensity to roll whilst cornering. Almost all cars today are fitted with anti-roll bars as standard equipment.

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SUSPENSION TYPES

Now let’s take a look at the actual suspension types. Car manufacturers in their infinite wisdom have given us a baffling number of different types suspension systems. Let’s take a look at some of the more common types. All suspension systems fall in two categories, non-independent and independent suspensions.

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NON-INDEPENDENT SUSPENSION

In a non-independent suspension, a rigid axle binds the left and right wheels. It is basically a solid bar kept in place by leaf springs and shock absorbers. You can find them on trucks and some SUVs but these haven’t been used in mainstream cars for years.

There are many different types of leaf-springs doing duty in different vehicles.
There are many different types of leaf-springs doing duty in different vehicles.

INDEPENDENT SUSPENSION

In an independent system, as the name says, the left and right wheels are allowed to move independently.

MacPherson strut: One of the most common types is the MacPherson strut. It’s a rather compact and lightweight suspension system that combines the shock absorber and coil spring into a single unit. The design means that they take up less space horizontally and as a result, it leaves generous room for packaging of the engine compartment and passenger cabin. MacPherson struts are also lighter, an advantage that reduces the overall weight of the vehicle. Another major advantage of this system is its ease of manufacturing, as well as the low cost of manufacturing compared to other stand-alone suspension systems. But it’s not perfect. Being a long, vertical assembly, it do not work well with sportscars that are normally lower. The MacPherson struts also have problems working with wider wheels and requires extra steering effort. Wide variations of vertical movement of the suspension, the kind you experience on very uneven roads, make it difficult for the tyres to maintain a 100 percent contact patch because the struts have a limited range of movement.

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Double-wishbone suspension: Another type of front independent suspension is the double-wishbone suspension. It typically uses two wishbone-shaped arms to locate or hold the wheel in place. Each wishbone has two mounting positions to the frame and one at the wheel, bears a shock absorber and a coil spring to absorb vibrations. Double-wishbone suspensions allow for more control over the camber angle of the wheel. The system is much more rigid and stable than other suspension systems, and handling performance is increased. The drawback of the double-wishbone suspension system is cost, as it is a more complicated design to produce. There are many parts to the system, and thus every time any of these malfunction of fail, your whole system fails. Repair, modification and maintenance costs and complexities for double wishbone suspension systems are normally higher due to these reasons.

Double-wishbone suspension is generally found in higher end cars.
Double-wishbone suspension is generally found in higher end cars.

Multi-link suspension: A third type of suspension worth mentioning is the multi-link suspension. This is the latest incarnation of the double-wishbone system. It uses three or more lateral arms, and one or more longitudinal arms, which can be angled in any direction allowing for better compromise between ride and handling. These are more likely to be used on performance cars.

SUSPENSION ALERTS

Now that you know how a suspension works, here are the signs that your car’s suspension needs your attention. If you start feeling every bump on the road or every bump on the road makes your car bounce, get your car’s suspension checked out.

You could do the ‘bounce test’, to check the health of your suspension. Press down on the front of your vehicle with all your weigh, ‘bounce’ it a few times, and then release it. If it bounces up and down more than three times, it’s time to head to the garage. Do the same for the rear suspension.

If you feel the vehicle pull to one side when you’re turning, it may mean that your shocks are failing. Here are some other signs to look out for – nose-dive during braking, rolling to the side when cornering, or squatting down during acceleration. Yes, these occur during spirited driving, but shouldn’t happen in normal driving.

This multi-link suspension is from an Audi.
This multi-link suspension is from an Audi.

Finally, take a look at your tyres. If the treads have worn out unevenly, this is a sign that your suspension isn’t holding the car evenly and is putting uneven pressure on the tyres. Time to get them checked.

Remember, the suspension system is attached to the wheels that put down the power through the car’s tyres. All the technology and engineering in the suspension system will go to waste if you use bad tyres. It is the four fist-sized patches of your tyres that translate engineering into emotion.

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