Inspecting & Evaluating Ride Control
Evaluating ride control condition, shocks and struts, requires road testing the vehicle and inspecting the ride control components.
The “Bounce & Jounce” method is more like ancient history than a valid test.
In days of old when cars were big & heavy, the suspension took a real beating so complete shock failures were common. It was easy to identify failed units by pushing down on a fender heavily a few times, then letting go and watching how many up & down body movements it took before coming to a rest. It seemed everyone had their own opinion about how many movements were acceptable and technicians would argue about who was right.
Right or wrong, this practice led to a common habit of waiting until shocks were completely failed before replacing them. A completely failed shock or strut is usually because most of the fluid has leaked out or the fluid valves are stuck open. Diagnosing complete failures is fairly easy to spot if fluid is dripping from the bottom, the tires are cupping or the body has excessive movement. So the subject of diagnosing shocks and struts is more about determining to what degree wear exists rather than just finding complete failures.
Here’s the bad news: Accurately measuring a shock or strut’s damping force can only be accomplished off of the vehicle utilizing specialized equipment. This is both cost prohibitive and impractical for most people. When the shock or strut is mounted on the vehicle, any measurement is affected by all of the other attaching parts such as; bushings, coil springs and ball joints. A variety of test equipment is available for on-vehicle testing, but none can claim to be 100% accurate and there aren’t any OEM specifications for this type of measurement.
The good news is that there is a variety of ways to evaluate a vehicle’s Ride Control instead. Ride Control is basically a vehicle’s ability to stop, turn, keep the tires on the road and the driver in control. (Although in the motorist’s opinion, ride control is more often perceived as ride comfort.) The shocks and struts performance affects every one of these abilities. Rating those abilities is meaningful to the motorist and can be accomplished without expensive equipment.
A practical method is to rely on a technician’s ability and experience to rate the vehicle’s current ride control conditions to the vehicle’s originally-designed capabilities. No on-the-vehicle method is absolute, but a good evaluation process based on accepted methods will provide the motorist with more reliable information to base maintenance decisions on.
Back to Bounce & Jounce? Unfortunately, that exercise isn’t very effective on today’s lighter vehicles and strut suspensions. It can reveal noises and offer some indications of wear, but it won’t provide enough information to rate component conditions. Evaluating ride control condition, shocks and struts, requires road testing the vehicle and inspecting the ride control components for visual evidence and eliminating other possible causes for conditions.
To help create consistent and more accurate evaluations we recommend:
- Ride control component & systems technical training
- An understanding of ride control drivability conditions
- A conditions rating guide
- Experience driving vehicles with new shocks and struts
To accomplish that, here’s some helpful information:
Conditions Rating Scale
Use this simple guide to compare current conditions to like-new condition or the improvement that new shocks/struts would provide.
Using this scale requires consistent vehicle road testing and some practice. Some exercises can be done in a parking lot while others will need some in-town driving speeds.
Consistent language and definitions for each condition is important to be able to communicate from technician; to service advisor; to motorist.
When you apply the brakes, the tires begin stopping but the vehicle body inertia tries to keep going forward. The result thrusts the front end downward and the back end upward. This imbalance puts stress on the front brakes and reduces the rear brake’s efficiency. The effect then makes controlling and steering the vehicle more difficult.
During cornering the vehicle body weight tries to lift & roll toward the outside of the turn. Controlling the weight shift or slowing the vehicle speed are the only ways to reduce the effect.
Small bumps and tire movements are transmitted throughout the vehicle. The ride can feel rough, harsh and noisy. This abrupt action affects both driver comfort and tire performance. The result is traction loss and usually along with that, less vehicle satisfaction.
During initial acceleration, like when leaving a stop, the front end rises and the back end lowers. Front end rise is controlled by the rebound damping in the shock. On a front wheel drive vehicle this results in traction loss and reduces steering control.
This can occur during braking, accelerating or cornering. When the tires can’t grip the road, for any reason at all, the result is loss of control: When the tires are bouncing or the vehicle body inertia is lifting or pushing the tires; when the tire tread is worn; when the tires are improperly inflated; or when the shocks and struts aren’t controlling tire and body movements.
Reacting to a bump is normal. But when the tire is allowed to over-react and move upward too aggressively, the travel must be stopped by a cushion or bumper stop. This is an indication that either the vehicle is being operated beyond its normal ability, such as being over-loaded or being driven too harshly. Or it could mean that the shocks are worn and can no longer resist wheel movement adequately.
Excessive left to right or sideways movements from; wind gusts, road conditions and steering movements. The shock or strut on one side is controlling a compression (or downward) movement while the opposite side is controlling a rebound (upward) movement. Steering corrections are required and can become difficult as the condition worsens.
When the tire is allowed to move up & down excessively, a rhythmic movement develops and an evenly-spaced wear pattern begins. Unlike tire balance conditions, the wear pattern frequency is greater from shorter tire movements that are not being dampened by worn shocks or struts. As the condition worsens, tire noise occurs along with traction loss and of course… tire damage.