VTEQ Braketesters

3) VTEQ Suspension tester

The second platform that the vehicle will drive onto with both wheels is the suspension tester (B).

The suspension tester will evaluate the whole suspension system of the vehicle.
The platforms of the suspension tester have very sensitive high speed recording weight cells. The vehicle's static weight is taken when you drive onto the platform.
The platforms will be oscillating throughout a frequency range while all the time the weight on the platform is measured.

VTEQ Suspension tester

The vehicle drives without hesitation onto the suspension tester, so that a sideslip test is performed. The suspension tester will start and tester will prompt the operator on the large flat LCD screen when to drive out onto the brake tester for each axle individually.

Theoretically will the weight on the platform be the same during an upward and downward motion. This would result in a 100% efficient shock absorber.

Screen visible just after the test. The operator can opt to re-do the test by pressing the remote control button F3.

The Eusama suspension test print on the previous page indicates on the left good suspension (85% efficient). On the right a problem at 15Hz (suspension bush lower arm), where the efficiency falls to 68%.

Description

The oscillating platform will 'throw' the wheel with a worn shock absorber up into the air, as it is far easier to move the wheel up than to move the wheel and the vehicle's body. The wheel will loose contact with the platform at worst, reducing the weight on the platform to zero kg's.
With a wheel weight of zero kg's there is no ability for the wheel to, for example transfer brake force onto the road.

The suspension needs to be checked throughout a certain frequency range as the bumps in the road are not equally spaced, nor is the speed of the vehicle constant….

There are testers on the market that will test only at one frequency, which is similar to pushing the vehicle down and watch or even measure the rebound. This test is totally pointless as a shock absorber can function perfectly at one frequency and let's go at a higher or lower bounce rate. Even in some cases have individual brand new shock absorbers been found to be faulty with these testers!

The bounce rate of a vehicle is also affected by worn bushes or ball joints. Every part in a vehicle has its own vertical inertia. When the frequency of the tester matches the frequency of a loose suspension part, the wheel will be 'thrown' of the platform at that frequency, reducing the weight on the platform. At any other frequency will the weight be relatively stable on the platform.

The results of a test with worn shocks look like this on the screen:

A good suspension system will show the coloured graph panel without a dip.

Where the graph dips (at around 11 to 12 oscillations per second), is the pressure (weight) on the platform the least. At higher frequency and at low frequency is the suspension performing perfectly.
The efficiency percentage of the suspension is taken at the frequency where the suspension performs at its worst, as that is the danger zone where a vehicle on the road will loose traction 'un-announced to the driver'.

The limits of what is acceptable, marginal or unsafe can be set by the operator or by a factory trained service person.

Efficiency bar graph changes colour at variable levels.

In this example are the marginal limits set at 40% efficiency and the fail limit at 20%. In most cases are these limits set at around 60% and 40%.

Continued