Auto Service World
Feature   June 1, 2001   by Auto Service World

Countertalk For the Counterperson: The 10 Minute Ride Control Inspection and Sale

Knowledge Building:

You and your installer customers both suffer from the inability of the car driving public to tell when their ride control has become ride neglect.

It’s not really their fault entirely. After all, deterioration of the bump-cushioning ability of shocks and struts occurs over many kilometers. Like a familiar face that stays familiar over the years, it hardly seems to change. What is required to see the difference is to look at the way it once was–like an old photograph–to bring the change into sharp relief.

Doing that for ride control is part inspection, part communication.

For installers, the inspection can be performed as part of regular service.

A test drive should be part of most types of service anyway, so the 10 minutes it takes to test for evidence of severe ride control deterioration can be combined with driveability and brake inspection.

For the consumer, it’s a simple set of checks that they can use to determine their own vehicle’s general condition.

Step One

Ensure that tires are all inflated to the proper specification. Don’t assume that 32 lbs. is correct, or that you can eyeball the tires. Get that pressure gauge out and measure it. Proper pressures are usually listed on the door jamb and/or in the owner’s manual.

The reason for ensuring tires are set properly is that they can mask or accentuate ride control problems, and can do the same for suspension and handling.

Step Two

Checking ride height can reveal problems with springs and other components that can be confirmed by a proper test drive.

Step Three

A proper test drive procedure should be routine for virtually any vehicle in for service. It can also be useful for consumers who are given a bit of information on what to look and listen for.

The key is a proper route that combines some variations in speed with turns and smooth as well as bumpy sections. A level railway crossing is a valuable addition. Installers should pick out a route and always use the same route. It provides a controlled environment.

Ride control engineers use a combination of quantitative measuring procedures as well as qualitative ride evaluation. The latter can be adapted to service situations.

On a scale of one to 10–with 10 being the best, most desirable performance–several ride parameters are taken into account. Balance, Handling, and Stability are rated for general performance, with the specific performance of ride control evaluated for Topping, Bottoming, Wheel Hop, Float, Shake, Noise, and Harshness.

The key for the person inspecting the vehicle is to identify the specific ride problem with the road surface. A clunking sound on a smooth road is one thing; when it occurs on the bumpy section of the route, it can mean quite another.


While car owners can perform a controlled test, their feedback can be questionable. They have, after all, become used to the way their car rides. This is where the need for communication comes in.

A simple, easily understood concept is that of the “Safety Triangle,” a concept promoted by Tenneco Automotive. While this specific concept has been advanced by a single manufacturer of ride control, it remains a valid viewpoint. The Safety Triangle concept considers the interrelationship of Brakes, Tires and Ride Control.

These three components work together to provide the driver with control and safety, particularly in poor driving conditions. In extreme cases, a severe deterioration in one can mask problems in another.

If the brakes perform poorly, the chance of breaking the tires loose is less than if they performed strongly. If the tires are poor, they’ll skid more and transmit less force to the vehicle, meaning dive and roll will be lessened. Also, just because there is little dive or roll, does not mean that the ride control is okay.

This is why any inspection of one of these areas should be accompanied by an inspection of all three.

One factor which many, probably most, drivers do not consider is the effect that ride control has on road adhesion. Most people think they just make the car ride nicely over the bumps. The fact is that degraded ride control can prevent the wheels from staying in contact with the road. No matter how good a tire is, it can’t find much grip in mid-air (or effectively in the air when it is unloaded).

For example, worn shocks or struts can cause excessive weight transfer, which reduces the ability of the tires to grip the road. And “tire hop,” a condition prevalent on poorly maintained road surfaces or experienced when a vehicle hits a pothole, compromises safety because the driver may lose some control over the vehicle.

Tenneco sponsored some independent studies by USAC a number of years ago that showed a degradation of stopping performance when one shock or strut was degraded to 50% of its capability. The German testing agency TUV came to the same conclusion regarding cars with stability control and ABS.

In the tests, a new VW Beetle fitted with 50% worn shocks was shown to have a braking distance up to 6 meters longer than the same vehicle fitted with 100% efficient shocks despite its ESP and ABS systems.

This is because when the ESP system tries to stabilize the vehicle, its braking distance increases, destroying the benefits of the ESP system.

A second test measured the performance of the vehicle by the highest entrance speed which could be maintained without hitting the cones. These tests found that a maximum speed of 62km/h could be achieved by the vehicle fitted with worn shock absorbers before losing control and hitting the cones. When the test was repeated with new shock absorbers, the Beetle achieved an improvement in driving speed of 3.3% or 64km/h.

In addition, it was found that worn shocks severely affect the efficiency of both the vehicle’s ESP and ABS braking systems. The tests showed that during evasive manoeuvres or emergency braking, the wheels lost contact with the road, reducing braking efficiency and driver control.

The message here is the same as before: technology can’t help a driver stay in control if the tires aren’t firmly planted on the road surface.

Informing customers of this is a strong step toward improving their understanding of the need for proper ride control.

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