Press Releases

The Hidden Danger of Worn Out Shock Absorbers

March 1, 2000

What is a shock absorber?
Shock absorbers might not be the most exciting part of a car, but along with tyres and brakes they are important elements of the safety of a vehicle. They are hidden beneath a car's wheel arches, so unlike tyres are not easy to check regularly for visible signs of damage and wear.

The role of the shock absorber is to keep the car's tyres in permanent contact with the road, helping to provide optimum grip, when cornering and braking. Shock absorbers are part of the suspension, so if the shocks are worn, the vehicle's ride and comfort is compromised.

The mechanics of a shock absorber all follow the same principle of controlling wheel movement by forcing oil through small holes, with the size or valving of these holes Ôtuned' to suit the chosen characteristics of each vehicle type Ð large or small, family saloon, load carrying estate, MPV, 4x4 or high performance sports car.

The dangers of worn shock absorbers
Most people are not even aware of the potential dangers of worn shock absorbers, or that the safety of their vehicle, its occupants and other road users is seriously compromised even if all other safety features are working correctly. An example of the extent of the problem is illustrated by two recent surveys. In Britain, it was found that over 6 million of the 25 million cars on the road had at least one worn shock absorber, while in Belgium, research showed that 20-25% of motorists are driving cars with worn shocks.

Monroe, the world's leading brand of shock absorbers, has identified the Ôtop ten' dangers associated with worn shock absorbers:

  • Reduced braking efficiency resulting in longer stopping distances
  • Reduced efficiency of Anti-Lock Braking Systems (ABS) and Electronic Stability Control (ESP)
  • Increased risk of skidding in the wet
  • Aquaplaning occurs at lower speeds
  • Less control when cornering or caught in a cross wind
  • Increased driver tiredness and reduced speed or response
  • Increased wear of tyres and other suspension components
  • Uneven/oscillating headlight level causing dazzle to on-coming drivers
  • Increased passenger discomfort
  • Increased risk of Ôsnaking' when towing

To highlight the danger of driving with worn shock absorbers, Tenneco Automotive - Monroe's parent company Ð has recently conducted a number of comparative tests between vehicles fitted with 50% worn shocks and 100% effective, Monroe Sensa-Trac with Safe-Tech shock absorbers. Having teamed up with TÜV, one of Europe's leading road safety institutes, the first tests showed that a multi-purpose vehicle (MPV) such as a Renault Espace with worn shocks can have a braking distance that's up to 4 metres longer than the same vehicle fitted with new shocks.

The second test featuring a new Volkswagen Beetle found that despite being fitted with the latest car safety systems such as Anti-Lock Braking (ABS) and Electronic Stability Control (EBS), with worn shocks the vehicle can have a braking distance of up to 6 metres longer than when fitted with new shocks. The final set of tests set out to demonstrate what effect ice and snow would have on a car's anti-lock braking and anti-skid systems, when combined with worn shocks. In the braking test, the results showed that a vehicle such as a Mercedes-Benz C250 Estate fitted with ABS but also with 50% worn shocks, had an emergency braking distance of 1.8 metres longer than the same vehicle fitted with 100% efficient shocks.

The same test conducted on a Peugeot 206 with ABS and 50% worn shocks, took an extra 1.2 metres to stop. The braking test results thereby prove that a car's ABS system does not function properly with worn out shocks. Finally, when comparing a car's acceleration on ice and snow, the tests found that a car such as the Mercedes-Benz C250 fitted with an ASR anti-skid system and 100% efficient shocks accelerated to a speed of 35.6 km/h (22.1 mph) in seven seconds, whereas the same car fitted with 50% worn shocks could only achieve 34.2 km/h (21.2 mph), a 16% improvement for the first vehicle. Furthermore, the time period of lost traction was 37% shorter with 100% efficient shocks compared to 50% worn components.

This test confirms the importance to check that a car's shocks are in good condition, even when fitted with ASR.

The importance of checking your shocks
The performance of a shock absorber deteriorates gradually and imperceptibly over time, during which the driver unwittingly adapts his or her driving to compensate for the wear and worsening condition and handling. As with most parts of a car that are in constant use, shock absorbers are inevitably subject to wear and tear.

Shock absorbers that are showing signs of wear can be recognised by a more accentuated load shift when cornering, poorer handling on uneven road surfaces and generally 'sloppy' suspension. A simple way of testing whether your car's shocks are worn is to carry out the 'bounce test'. If a vehicle oscillates more than once after downward pressure is applied to the bonnet of the car, this could well signify that the car's shocks are worn. Additionally, visual checks for oil leakage and uneven tyre wear can be carried out. Tenneco Automotive recommends that shock absorbers should be checked annually or every 20,000 kms (12,000 miles) by a qualified mechanic. This allows sufficient time to take action to ensure the safety of the driver, their passengers and other motorists is maintained. If the car's shocks do need replacing, it is extremely important that they are replaced in pairs - just like brake pads so that there is an even balance on both sides of the car.

The Monroe product range
Supplying over 98.8% of the cars on Europe's roads today, there are Monroe shock absorbers for virtually every make and model of car. The new Monroe Sensa-Trac with Safe-Tech System shock absorber is available for over 90% of Europe's cars. Designed to provide maximum 'tyre to road' contact in all driving situations, this 'intelligent' shock absorber offers the benefits of electronically controlled suspension without the high cost and complex electronics. Monroe products also include a standard line consisting of Radial-Matic and Gas-Matic shocks and products available for special driving situations such as caravan and trailer towing (Ride-Leveler and Level-Light), and for off road use (Gas Magnum 4x4). The brand also includes the Van Magnum product line for most light commercial vehicles (LCV), and Magnum for the heavy (HGV) goods vehicles and trailers.

Background information
Tenneco Automotive's mission is to continually examine and improve its range of ride control systems ensuring the very best products are manufactured for car companies and the aftermarket it serves. The company supplies one in every four shock absorbers globally, around 24 million components a year for customers in Europe, the Middle East and Africa. Car companies include Audi, Daewoo, DaimlerChrysler, Ford, General Motors, Isuzu, Mitsubishi, Nissan, Renault, SEAT, Skoda, Toyota, Volkswagen and Volvo. Tenneco Automotive is a $3.3 billion company, with 81 manufacturing facilities and 24,000 employees worldwide, and has its European headquarters in Brussels.