What’s so important about shock absorbers?

• What causes a vehicle to skid?
• What does ESC do?
• How do shock absorbers work?
• Match replacements with the vehicle’s original fitment

Despite the increasing popularity of electric vehicles, there are many parts of your car that are common to both conventionally powered and electric vehicles, as well as their hybrid counterparts, and this will remain so for the foreseeable future. These include wheels and tyres, brakes and steering components, but also the suspension.

Along with so much of a modern vehicle, many of these areas are controlled by sophisticated onboard computers that are constantly assessing current driving conditions and liaising with components every millisecond to respond appropriately. Electronic stability control, or ESC, for example, is an electronic system that helps prevent a vehicle from skidding.

What causes a vehicle to skid?

Most serious accidents occur when the vehicle is being driven too fast for the conditions and goes beyond its traction limits, which can lead to oversteer (when the rear wants to overtake the front and the car spins around) or understeer (when the front can’t turn effectively and wants to go straight on), for example.

What does ESC do?

ESC however, can reduce skidding by up to 80%, as it senses when the vehicle is leaning or ‘rolling’ too far or when the tyres begin to lose traction with the road surface and can instantly reduce engine speed and apply the brake on an individual wheel, just enough to keep the vehicle under control.

Despite ESC becoming a common safety feature on most of the cars on the UK’s roads, its effectiveness is limited by the condition of the vehicle’s tyres and suspension.

When the ESC is calculating the necessary corrective measures to avoid a skid, it assumes the suspension and the tyres are in good condition, just like they were when the car was new. However, if it detects a traction problem and sends a signal to apply the brake on the rear left wheel, but the tyres are worn, the vehicle might not have the required grip available for that corrective measure to prevent it from going into a dangerous skid, which is why tyre monitoring and maintenance is so crucial to safe motoring.

How do shock absorbers work?

Alongside having tyres of good condition, shock absorbers are vital in keeping them firmly pushed in contact with the road. This is because, the more surface area of the tyre that is in contact with the road, the more traction it has to steer and brake. While the vehicle’s coil springs compress to reduce the impacts of bumps in the road, the shock absorber allows the spring to extend smoothly back to its level ride height, and in doing so keeps maximum contact between the tyre and road.

So, just like the worn tyres example, if the ESC sends a message to apply the brake on the rear left wheel and the shock absorbers are worn, the vehicle may still not have the required traction available to avoid skidding.

In common with most of the parts on your car, over time the performance of the shock absorbers will gradually deteriorate. This is because the hydraulic oil, which incidentally is also still used in ‘gas’ shock absorbers, passes through metal valves inside the shock absorber as it compresses and extends, gradually causing wear. Typically, the oil will pass through these valves almost 400 times every mile, so as they fatigue, they let more oil through with each movement, resulting in a reduction in fluid resistance that weakens their ability to absorb the shocks from the coil springs. This means your vehicle will not be quite as ‘firm’ or have the same handling qualities as when it was new.

Original equipment producers, supplying the vehicle manufacturers with shock absorbers, agree that after 50,000 miles they no longer operate to the standards the car maker intended and will also not provide the level of road surface traction that the ESC requires to do its safety critical job to the optimum.

It is therefore, very important that once your vehicle has covered this mileage, the condition of your shock absorbers is assessed by a professional technician.

Match replacements with the vehicle’s original fitment

Should they recommend the shock absorbers are replaced, it is essential to choose a trusted supplier and never downgrade the technology. So, if the vehicle has gas shock absorbers as standard for example, they should not be replaced with purely oil filled versions, as the vehicle should always be restored to its original performance level, or better.

Attempting to cut costs by opting for a lower quality alternative will inevitably mean fitting a product that is likely to have some of its vital components, such as the internal rebound springs, stripped out to save cost, meaning they simply cannot perform to the level expected and required for the correct function of the ESC and therefore, for the safety of you and your passengers.