Here in Australia, the advice given by the National Heavy Vehicle Regulator is that workshops should use dynamic weight when assessing a brake system’s efficiency. However, both the dynamic and the static weight, as well as deceleration, should be accurately recorded and shown on all reports.
In this article, we will look at some of the differences between static and dynamic weight when it comes to roller brake testing.
What Is Static Weight and Static Deceleration?
Before we look at dynamic weight, first it is important to understand static weight. Static weight is the measurement taken as soon as the vehicle is put on the brake tester. Essentially it is dead weight. Static deceleration would be the deceleration measurement taken using the vehicle’s static weight.
What Is Dynamic Weight And Dynamic Deceleration?
When talking about dynamic weight, what is being referred to is the weight that is measured when the brake test has finished because of any of the wheels slipping by approximately 30%.
Dynamic deceleration is the deceleration experienced by the axle or the vehicle when using dynamic weight.
Measuring Deceleration
When measuring deceleration, it is usually displayed as kilonewtons per ton (kN/T). The other types of metrics often used are the percentage of gravity (%g) or metres per second squared (M/S/S).
Measuring Axle Weight
When measuring the axle, you also have two different options: static weight and dynamic weight.
When testing brakes using roller brake testers, the wheels are often lifted out of the rollers and moved backwards, which causes some weight change on the axle, especially when it comes to vehicles with traditional suspension systems.
In some cases, there can be axle weight differences between static and dynamic weight of as much as 40%!
Testing Light Vehicles
Testing very light vehicles or trailers present a unique problem as they are often too light to perform accurate tests as they are likely to slip too early. This is why dynamic weight is not the only factor taken into consideration and why static weight is also used.
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