As more utes become used for work and play, load carrying and weight distribution are becoming a concern. Here’s what you need to know.

Hi Practical Motoring,

Can you assist with some information or clarification, please? I read on a forum a discussion around the chassis failures of some dual-cab utes and the overloading of those utes.

The comment I would like clarification of is this… the writer claimed that a dual-cab ute fitted with five seatbelts, was required to ‘reserve’ about 400kg (5 times 80kg passengers) of the payload to be ‘contained’ within the passenger cabin. So, for example, if a dual-cab ute had a payload of 1000kg then only 600kg (1000kg payload less the 400kg for passengers) would be available for barwork, fuel, tow ball load, tray load etc. Is this correct? Or can the 1000kg payload be distributed ‘anywhere’ across the chassis? Thanks.

Your friend on the forum is mostly wrong. As ever though, it’s not a straightforward answer.  

Any vehicle, including a ute, has a GVM or Gross Vehicle Mass. This is the maximum it is allowed to weigh, and let’s say that’s 3000kg. The unladen weight might be 2000kg, so then we can carry 1000kg which we term the payload.  

The first trap is relying on the payload figure of 1000kg. The problem here is that while the GVM is fixed at 3000kg, the unladen (kerb, or tare weight) varies a bit depending on engine, trim level and so on. And “unladen” is open to interpretation; kerb and tare are not the same, and there are even variations within the same term – whether that weight includes a 75kg driver, amount of fuel and so on.   

Modifications and accessories will not be counted either. The unladen weight stated by the manufacturer probably wouldn’t include a towbar for example, and it definitely wouldn’t include bullbar, winch, canopy and all the other gear we add to touring 4WDs, all of which comes out of the payload.  

Calculating how much you can carry (payload)

So if you want to know how much you can carry then the only true way is to unload your car, take it to the local weighbridge and weigh it, then subtract that weight from the GVM to find the payload. The answer is usually depressingly small. In the case of some wagons (big ones with small payloads like the Nissan GU Patrol and Toyota LC200 Landcruiser), some larger-boned owners who like to take a lot of gear have realised they cannot legally get in the car once it’s loaded for a trip. 

Correct weight distribution

Now onto the subject of weight distribution – vehicle owners do not have complete freedom to place a load where they please, and there are two very specific limits which explain why. These are the front and rear axle loads. In the case of our fictional vehicle with a GVM of 3000kg, the front and rear axle loads might be 1600 and 1800kg, totalling 3400kg. When you load a vehicle you need to respect both of these limits, and that instantly places restrictions on where the weight can be placed. A problem for load-carrying vehicles is where the sum of the axle loads does not exceed the GVM, which means the vehicle can only be loaded with very precise placement of the weights across axles.  

However, there is no instruction from any manufacturer that we are aware of which says a vehicle must split its weight specifically in parts across the cab and the tray. The axle loads and GVM are the important limits. Fleet managers might place specific restrictions though, ensuring that at any time the vehicle should have sufficient spare payload for 5 passengers, but that’d be a local, company-specific rule.

How the chassis can become overstressed due to payload

But there’s more. If you add load in front of the front axle, or behind the rear axle then you are increasing load on that axle by more than the weight added. For example, a bar and winch weighing 90kg will add more than 90kg to the front axle. Similarly, a 250kg ball weight 1.5m behind the rear axle will place more than 250kg of weight on the rear axle – exactly how much is dependent on the wheelbase of the vehicle, but with a 3m wheelbase it’d be 125kg to total 375kg – and the front axle load will be reduced in turn by 125kg. And then we get stress on the chassis which is balancing these forces.   

The other area of particular concern with utes is the tray loading. The manufacturer will have provided specific points where the load is to be borne, both by the payload on the back and the suspension components. Placing load anywhere else is asking for yet another case of cracked ute chassis, and that includes adding different load bearing points as well as changing how the suspension transmits loads to the chassis – an issue often seen with additional springs. The problem is that the modern ute is often overloaded, so owners add very stiff suspension, and the vehicle is so powerful and capable it still works…up until the time it breaks after having been driven over corrugations while overloaded, with the load in the wrong place, and sometimes with a heavy towball mass well behind the rear axle.  

So the summary is: keep the vehicle below GVM and axle loads and only use manufacturer-supplied load bearing points.

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