When is a 4 tonner not a 4 tonner ?

FAW 4,5 ton workhorse

Some manufacturers are advertising their vehicles as '4-tonners' while, in fact, these vehicles are not legally capable of carrying 4 tons of freight. This was pointed out to FleetWatch by FAW after the company lost orders to a competitive manufacturer which, FAW claims, 'erroneously' advertises its vehicles as 4-tonners. Many operators are thus buying these vehicles in the belief they will carry 4 tons of payload. They will - but not legally, claims FAW who asked FleetWatch to investigate the subject. Jack Webster, our correspondent on legislation, has come up with some interesting observations.

The question 'when is a 4-tonner not a 4-tonner' gives rise to what is probably the most frequent inquiry when discussing the capacity of motor vehicles, particularly goods vehicles. Of key relevance, however, is to determine what we are talking about - gross mass, or payload mass? Until this is known, it is not possible to give an accurate answer.

There is obviously a big difference and in order to gain a complete understanding and appreciation of the ramifications, a full explanation is given here:

1. If gross mass is to be used as the vehicle capacity, the permissible maximum vehicle mass must be determined, which is denoted with the Symbol "V". The "V" of a vehicle is obtained by taking the least of the following factors:

• The manufacturer's gross vehicle mass rating of the vehicle, denoted GVM. This can only be determined by the manufacturer - not the dealer, not the operator - only the manufacturer;
• The carrying capacity of the tyres as determined in the load and inflation tables published and gazetted by the South African Bureau of Standards - SABS 1550;
• The maximum carrying capacity of roads as prescribed in Road Traffic Regulation 240.

While the least of these factors determines the "V", a further consideration is the distribution of the load to ensure that the permissible maximum individual axle massloads are not exceeded.

Now, let the capacity of a vehicle be determined according to the mass of the payload which can legally be carried on the vehicle. In this case, the determination of the maximum legal payload is obtained as follows:

• Determine the "V" of the vehicle in the manner described in 1(a), (b) and (c).
• Determine the unladen mass of the vehicle. This is not the tare (which does not include fuel and the on-vehicle-personnel). It is the vehicle complete and ready to operate. Also, the unladen mass must include the body.
• To establish the payload mass, the unladen mass is subtracted from the "V" and the load distribution checked to prevent exceeding any individual permissible axle massload.

Using the information provided to FleetWatch for the 2001 edition of TruckWatch, the appended two tables contain an analysis of available 4 tonners based on approximately 4 tons gross mass and 4 tons payload mass.

An analysis of these two tables reveals several important things which potential buyers of vehicles must take into consideration when referring to the capacity of a particular make or model.

• Is it the maximum gross mass of the vehicle or the maximum achievable payload mass to which we are referring?
• When we refer to gross mass, we should be referring to the permissible maximum vehicle mass ("V"), and not the manufacturers' gross vehicle mass ("GVM").
  
• When we refer to the unladen mass of a vehicle, we must not be confused between tare mass and unladen mass.

The "tare" does not include fuel, driver and anything not a part of the vehicle but unladen mass includes everything except payload.

Finally, analysing Table 1, it will be seen that of the vehicles available in South Africa with a permissible gross mass (V) of just over 4 tons, the maximum achievable payload is just over 2 tons, and Table 2 reveals that to achieve a payload of 4 tons, the "V" must be between ± 8 000 and 9 000 kg permissible maximum vehicle mass ("V").

In reality, if true comparisons are to be made between makes and models of goods vehicles, surely the maximum achievable payload should be the basis of comparison since it is the payload which generates the revenue which a vehicle is capable of earning.

TABLE 1

4 TON GROSS MASS VEHICLES

TABLE 2

4 TON PAYLOAD VEHICLES

Additional article

• Clearing the 'Combi' misnomer