Everything about a rigid truck

In general, the rigid truck will have a maximum gross vehicle mass which is over 3500 kilograms. It will have 2 axle sets, drivers’ position, motive power, steering system and single rigid chassis.

The maximum dimension limits


  • The maximum is 2.55 metres. The extra width is allowed for side marker lamps and direction indicators.
  • Collapsible Mirrors are also allowed which should not extend more than 240 millimetres be on the side of the vehicles or in its trailer. It should be 1.49 when it is measured from the trucks longitudinal Centreline.
  • Central tyre inflation system should not extend more than 75 millimetres and reach the outside of the tire on the drive axles of a heavy motor vehicle.
  • It will have a hubodometer but never more than 15 beyond one side of the truck. The hub odometer is on the axle which causes the least over width.
  • Next is the cab exterior Grab rails which is not more than 1.325 metre when measured from vehicles longitudinal Centreline.
  • There is a provision to fit cameras and close-proximity monitoring systems to be mounted on the side exterior of a vehicle not be more than 70 m from the sidewall.
  • The devices which improve the aerodynamic performance of the truck can be used to extend not more than 25 millimetres from the side of the truck.


  • The maximum height from the ground is 4.3 metres.
  • The stability requirements restrict the height of the body or the load of the class sometimes there operating gross mass.
  • A load of a truck will have a great impact on the stability of the truck. The load has to be arranged with special care in such a way that the mass and height are appropriate for the design of the vehicle.

Static roll threshold

Which is the measure of the potential of a vehicle to roll over sideways? The trucks which have a low SRT will roll over than the trucks with higher SRT. This is likely to happen especially when the truck is travelling around sharp bends and in a sudden emergency. In clear terms, the lower the SRT, the less stable the vehicle.

How to improve the static rule threshold?

In order to improve the stability of the trucks, the gross vehicle mass must match to certain specified limits. Suppose a rigid truck does not meet the specified limit, the stability can be improved, by operating the truck with reduced mass. The truck can also be modified to have a sufficient roll stiffness which will pave the way to operate safely with maximum carrying capacity.

How the assessment is carried out?

The most common way of carrying out the assessment is by using the SRT calculator. It is a computer program. It is a kind of a computer simulation that which takes into account the trucks loading characteristics, for instance, deck height.

It also considered the trucks mechanical components that which can affect the roll stiffness. These components will include suspension type, track width, wheels and tires.

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