The GVM conundrum

When looking at service vehicle choices, there’s more to consider than gross vehicle mass alone.

The gross vehicle mass of the average light utility has increased substantially over the last 10 or 15 years. For instance, a 1998 Toyota Hilux had a GVM of 2730 kg, versus 2835 kg in the 2014 offering. Without more information, an unsuspecting customer may think that equates to a higher payload capability, but this is far from the truth. In reality, the ’98 Hilux featured a 1341 kg payload and the later model just 1155 kg. There’s obviously more to consider than GVM alone, so let’s break it down.

Calculating payload

In order to correctly establish utility requirements prior to initial purchase, buyers should calculate payload to ensure ultimate operation of the vehicle within safe limits. Correct chassis selection will ensure the long life of the vehicle, sensible fuel economy and good handling. To assist in payload calculation, we’ve provided the following guide on common terminology, along with some calculation examples.

Gross vehicle mass (GVM)

GVM is measured in kilograms and displayed on the vehicle compliance plate (usually found under the bonnet on the firewall) as well as vehicle specification sheets. The GVM is the maximum permissable weight of a fully loaded vehicle including the vehicle itself, the driver and passengers, accessories, options and any type of truck body.

Kerb mass (KM)

KM is the mass, or weight, in kilograms of the vehicle as a cab chassis with no driver, passengers, payload or truck body. The KM of utilities varies from model to model.

Payload (P)

Payload is the mass, or weight, of cargo/goods/tools and people that the vehicle is permitted to carry.

Occupants

Every person in a light truck is considered an occupant and is assumed to weigh 75 kg. The total number of occupants for any truck is shown on the vehicle compliance plate and usually on the vehicle specification sheet.

Vehicle compliance plate (VCP)

The VCP is an aluminium plate affixed to the firewall that shows the make and model of the vehicle, the GVM and the recommended number of occupants.

Tare

Tare is not the same as kerb mass and should not be used for these calculations.

Calculating payload (P)

Payload (P) in kilograms is the GVM minus the following items: KM; weight of the occupants; weight of fuel, oil and water; weight of any fitted options (towbar, bull bar, etc); and the weight of the truck body.

Presented as an equation, P = GVM - (KM + fluids + occupants + options + truck body/tray).

Managing inventory

Payload is a variable dictated by the ability to manage inventory and organisation is the key. Removing tools and equipment from a vehicle that aren’t required on a day-to-day basis will reduce excess weight. Rationalising consumable inventory eg, swapping a 40-litre drum of oil for a 20-litre drum or carrying two tubes of silicone instead of a carton will save a few more kilos.

Reducing unnecessary weight allows the payload to be used for priority equipment. Revising your equipment inventory on a regular basis would ensure you have sufficient stock and the right tools each time your vehicle arrives on-site.

The consequences of exceeding GVM

Exceeding the GVM of a vehicle leads to a number of issues:

• Increased running and maintenance costs: The vehicle is working harder and under excess strain in terms of suspension and brakes.
• Poor handling: Less control of steering and braking makes driving more difficult. In turn, this leads to compromised safety for the driver, passengers, other vehicles and pedestrians.
• Warranty: In the event of an accident, warranty can become null and void if the vehicle has exceeded the GVM capacity as specified by the manufacturer.
• Liability: At best, an overloaded vehicle can incur a hefty fine. At worst, a vehicle involved in an accident occasioning injury or death can lead to devastating outcomes including gaol sentences for responsible parties.

Duty of care considerations mean others in the chain have a shared participation in any negligent behaviours, which is a sobering reminder for fleet managers and operators when determining the ideal vehicle choice for service teams.

Spreading the payload

It’s not uncommon to see a ute so overloaded at the rear of the tray that the front wheels are almost off the road. This means all of the payload weight is on or behind the rear axle, creating an unbalanced vehicle, which will render the steering light and ineffective, contributing to a more hazardous driving environment.

Heavier load items should ideally be positioned nearer to the vehicle cab, between the front and rear axles, resulting in a more even load spread and safer driving experience.

Too little payload capacity for the job?

If the required GVM can’t be effectively handled by a light utility, what is a fleet manager to do? Essentially, there are three choices: continue as is, overload the vehicle and hope nothing goes wrong; supplement the fleet with additional light utilities to carry the excess gear; or, upgrade to a medium truck that can carry a larger payload without compromise.

The upside of option number three is that service bodies and canopies can be fitted to standardise the load and create protocol for the carrying of additional payload weight.

While the one-tonne ute is a popular choice for field service teams, the heavy loads, tools and equipment frequently needed for a ‘workshop on wheels’ mean that a larger service body is often a better choice. Interior fittings can be developed to hold specific tools and equipment and to allow for the weight of those items in the payload distribution.

With so much at stake, it’s clear that GVM alone is not a sufficient indicator of vehicle suitability and that required functionality and load capability should be carefully considered before making a choice.

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