Weight watchers – understanding your vehicle’s load capacity

The larger load space and superior versatility of SUVs and double-cabs make them ideally suited to many families’ lifestyles, but do they all offer the required load carrying capacity for your needs?

Image: Jetour

One of the key drivers of the move from sedans to both SUVs and LCVs as family vehicles has been their practicality – large volume load space and flexible seating in the case of SUVs, and the combination of five seats with a versatile load box in the case of double-cabs. For owners, this additional load volume comes with the assumption that the reasonable utilisation of that space will not see them exceeding their vehicle’s maximum permitted load capacity. A recent check of the usable load capacities of some SUVs and LCVs has revealed this isn’t always the case and that some of these vehicles might fall short of the expectations, and requirements, of some users.

Unfortunately, this usable load capacity is typically not specified in passenger-vehicle brochures or spec sheets, requiring owners and prospective buyers to understand some vehicle load terminology and perform a simple calculation to confirm that the load capacity meets their needs.

Understanding the terminology

A vehicle’s Tare Mass (T) is the weight of the vehicle, including all standard equipment and fluids, but excluding fuel. The figure is primarily used in certification but can also be used as a base for determining maximum trailer weights. For motorists, Kerb Mass (Tare plus a full tank of fuel) is the more practical figure. This, along with the GVM (Gross Vehicle Mass – the maximum permitted weight of the vehicle, made up of the vehicle itself, fuel, occupants and any loads/cargo) is usually specified in vehicle brochures and spec sheets.

If any non-standard accessories such as a roof rack, bull bar or canopy are fitted, these must be included as part of the load/cargo. When a vehicle is used for towing, the downward load on the tow ball (Trailer Nose Weight) also needs to be included as it is an additional load on the vehicle. The GVM figure is determined by the manufacturer and, among other factors, is used in the calculation of suspension travel, spring rates and braking performance. It is also used in vehicle homologation and thus becomes a legal, rather than just a design, limit. The concept is easy enough to understand but without access to a weighbridge, vehicle owners need additional information to calculate just how much can be loaded into their vehicle without running the risk of exceeding the GVM.

Payload is the maximum load a vehicle can carry without exceeding the GVM and can be calculated as the difference between GVM and Kerb Mass. While the term may not be commonly used for passenger vehicles, it is no less a consideration than it is for commercial vehicles, where it is sometimes defined as Gross Payload which includes the weight of a driver and passenger, or Net Payload which excludes them and is effectively the weight of goods which can be carried.

For those who tow, Gross Combination Mass (GCM) is a key factor, as the legal limitations include whether the trailer is braked or unbraked, and whether the driver holds the correct licence. Subject to any limitation provided by the vehicle manufacturer, an unbraked trailer up to a maximum GVM of 750 kg may be towed, provided that the GVM of the trailer does not exceed 50% of the Tare of the towing vehicle. This 750 kg trailer GVM limit is the same towing limit which applies to drivers holding a Code B licence – the standard licence for drivers of vehicles with a Tare not exceeding 3 500 kg. Braked trailers with a GVM not exceeding the Tare of the towing vehicle may be towed by holders of EB licences, again within the 3 500 kg vehicle Tare (and trailer GVM) limit.

Image: Suzuki

Vehicle data plates

Unfortunately, vehicle data plates generally don’t provide all of the information required to establish the permissible payload, and reference to a brochure, spec sheet or owner’s handbook is needed to determine the Kerb Mass. Data plates are primarily a convenient reference for policing purposes and list GVM, GCM, GA 1 and GA 2, with the GA figures referring to the maximum front and rear axle loads. These figures represent the maximum permissible load on each axle and provide some leeway for load distribution, but their sum when measured may not exceed the specified GVM.

Does the specified load capacity meet your needs?

It’s important for owners and prospective buyers to determine their load capacity requirements and then confirm the load- carrying capabilities of their existing vehicle or intended purchase to ensure they remain within the law. Deducting the Kerb Mass from the GVM will provide a payload figure, which is the maximum weight of the occupants, any fitted accessories, and the load to be carried.

If the heaviest payload required for your midsize, five-seater family SUV is three adults, two younger children and a boot full of holiday gear, then a payload of 375 kg would probably suffice. This would be calculated as 3 x 75 kg for the adults, another 75 kg for the children combined, and allow for a load of up to 75 kg in the boot. A check of a sample of vehicles in the category revealed that the majority could carry payloads ranging between 375 and 450 kg with an exceeding 600 kg. Worth noting is that despite their size, some models offered payloads as low as 300 kg, effectively limiting their use to smaller families and light loads. At the other extreme, if golfing weekends with four friends are the norm, the occupants, their golf clubs and even limited luggage could push the payload requirement to between 550 and 600 kg, limiting the vehicle options to a few soft-roader SUVs or one of the more rugged body-on-frame SUVs.

The payloads of most double-cab 4×4 LCVs range between 800 and 1 000 kg, which will enable them to generally meet most of the load requirements of overlanding – a full load of adults, aluminium canopy, rooftop tent, fridge/freezer, and some additional fuel, water and equipment. If loading beyond the above, it is worth checking actual loaded vehicle weight to confirm compliance.

The implications of overloading

Operating a vehicle that exceeds its GVM is a contravention of the National Road Traffic Act and can result in a fine, AARTO demerit points, and even impoundment of the vehicle. In addition, if you’re involved in an accident and it is proven that the vehicle was overloaded, your insurer might repudiate the claim. Another aspect that’s not to be overlooked is that overloading can compromise vehicle stability, handling and braking, especially at higher speeds. As an owner, or prospective owner, of an SUV, taking the time to complete a few basic calculations is all it takes to avoid the legal, financial and safety implications of operating a vehicle at more than its maximum permitted weight.

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