HEAVY WITH SUSPENSE
UPGRADING a 4x4’s Gross Vehicle Mass (GVM) rating is slowly becoming more popular with off-road tourers (it is a common practice in the mining industry) and has come about, in part, due to the fact new 4x4s are, in standard form, quite a bit heftier than they were 15 to 20 years ago. The result is a reduction in load-carrying capacity; once you throw in a family of four, plus all their gear, a spare wheel/tyre, recovery equipment, and then take into account fitted accessories such as bullbars, cargo drawer systems, roof racks and spare-wheel carriers, you can easily exceed a vehicle’s GVM. A heavierthan-designed vehicle puts more stress on essential components such as suspension, tyres, brakes and the chassis, rendering the vehicle illegal and unsafe. Compliance testing for GVM is one of the most timeconsuming, with so many components affected by the additional weight.
Automotive Safety Engineering’s Grad Zivkovic explained: “GVM is a major upgrade. The vehicle needs to be reclassified and another compliance plate issued. There are serious consequences (if GVM is exceeded on a standard vehicle) if it is, for example, upgraded too much and the brakes are not designed to dissipate the increased
heat they generate during braking as a result of trying to pull up the extra weight.
“Another design rule we use for testing GVM is the stability control test for when you’re changing lanes at different speeds – 60, 80 and 100km/h – where the heavier load would also affect suspension (springs and shocks) during a preventative manoeuvre.”
So the GVM upgrade and the compliance testing needs to look at all of the separate components – brakes, suspension, chassis – to ensure that the vehicle is just as safe and performs just as effectively as before the GVM upgrade. It also needs to perform as it was designed to in all conditions, including if the driver needs to swerve suddenly, which means testing needs to be done in a controlled location.
“This type of testing has to be done away from the general public,” Grad affirmed. “If you have very soft suspension, for example, with the higher centre of gravity and increased weight, the shock absorber may not be able to dampen in the time the vehicle moves or rocks sideways, and the vehicle can overturn. We usually use full helmets, race harness and things like that.”
Due to the complexity and the fact that the vehicle’s overall performance is affected, a GVM upgrade process always involves retesting to meet the relevant ADRS for the particular vehicle tested.
The retest also provides a summary of evidence in relation to the upgrade, according to Steve Sampson of ARB. Steve sent me a copy of what ADRS are accounted for during this process (and it is vehiclemodel dependent; as an example, a 200 Series GX is classified differently to the GXL, so required ADRS differ between models) and I counted more than 30.
It’s a serious business, but it provides assurance for those who pay for a GVM upgrade via an aftermarket manufacturer dedicated to the best and safest product.