Information for heavy vehicle drivers

Heavy rigid motor vehicle definitions and specifications

A heavy rigid motor vehicle is a vehicle with a driver's position, a steering system, motive power and a single rigid chassis.

Special vehicles registered as a single vehicle but that have a chassis split into two dependent parts that are connected by a permanent steering pivot are also classed as rigid vehicles.

Dimension requirements

Vehicles with dimensions greater than those set out in the diagram below are classed as overdimension vehicles. For more information, refer to Factsheet 53, Overdimension vehicles and loads, or contact the Overdimension Permit Issuing Agency on 0800 OVERSIZE (0800 683 774) or fax 06 953 6313.

(1) Forward distance

Forward distance for a rigid vehicle is the distance from the rear axis to the front of the vehicle or its load, whichever is foremost (excluding collapsible mirrors).

The maximum forward distance for heavy rigid vehicles without a tow coupling is 9.5 metres. Heavy rigid vehicles with a tow coupling are restricted to a maximum forward distance of 8.5 metres.

(2) Maxmimum height

The maximum height above ground is 4.25 metres. An additional 25 millimetres is allowed for tarpaulins, lashings, straps, chains, covers and related connectors and tensioning devices that aren't permanently or rigidly fixed to the vehicle.

(3) Overall length

Maximum length for a heavy rigid vehicle (including load, but excluding collapsible mirrors) that is not towing a trailer is 12.6 metres.

(4) Rear overhang

The distance from the rear axis to the rear of the vehicle or its load, whichever is greater.

For a heavy rigid vehicle with a non-steering axle as the rearmost axle, the maximum rear overhang is either 4.0 metres or 70 percent of wheelbase (A in the diagram below), whichever is less. In the diagram below, the rear axis is at the centrepoint of the non-steering axle or axles.

* For a heavy rigid vehicle with a steering axle as the rearmost axle, the maximum rear overhang is either 4.25 metres or 70 percent of wheelbase, whichever is lesser.

(5) Wheelbase

Wheelbase is measured from the rear axis to the centre of the foremost axle.

Front overhang

Maximum front overhang, measured from the front edge of the driver's seat (in its rearmost position) to the foremost point of the vehicle or its load, is 3 metres.

Width

The maximum width is 2.5 metres, or 1.25 metres from each side of the longitudinal centre line of the vehicle (excluding side marker lights, direction indicators and the bulge towards the bottom of a tyre). The only extra width allowed is:

• 240 millimetres each side for collapsible mirrors
• 25 millimetres each side for J-hooks (to secure crates or bins) or ropes, lashings, straps, chains, connectors and tensioning devices that aren't permanently or rigidly fixed to the vehicle
• 75 millimetres each side of drive axles only, for the air hoses of central tyre inflation systems
• 75 millimetres for hubodometers on a non-lifting, non-steering axle that causes the least over-width
• 50 millimetres for exterior grab rails on the cab (to help the driver and passengers get in and out safely).

Axle sets and weight limits

A heavy rigid vehicle must have a front axle set consisting of a:

• single axle set , or
• twin-steer axle set.

A heavy rigid vehicle must have a rear axle set consisting of a:

• single axle set, or
• tandem axle set, or
• tri-axle set.

Single axle set means either one axle or two axles where the centres are spaced less than 1 metre apart.

Tandem axle set means two axles where the centres are spaced no less than 1 metre and no more than 2 metres apart.

Tri-axle set means three axles where the centres of the first and third axles are spaced no less than 2 metres and no more than 3 metres apart.

All the axles contain an equal number of tyres. None of the axles is a single standard-tyred axle.

Twin-steer axle set means a tandem axle set with single tyres, with both axles connected to the same mechanism in order to steer similarly.

Maximum allowable mass (weight) on axle sets (kilograms)

Note: all weights are in kilograms.

Note: for weights on oscillating axles and other axle combinations not shown here, see the Land Transport Rule: Vehicle Dimensions and Mass 2000.

In addition to having a mass on their axle sets within the limits shown in the diagrams above, heavy vehicles also need to have a total mass that is within the limits set out in the following table, when the distance from any axle in any set to any other axle in another set is measured.

Maximum vehicle and axle mass

The following table sets out the maximum sum of mass on any two or more axles that together do not constitute a single tandem axle set, single tri-axle set or single quad-axle set.

Distance between centre of first axle to centre of last axle (metres)	Maximum gross weight (kilograms)
1.8 or more, but less than 2.5	15,500
2.5 or more, but less than 3.0	17,500
3.0 or more, but less than 3.3	19,000
3.3 or more, but less than 3.6	20,000
3.6 or more, but less than 4.0	21 ,000
4.0 or more, but less than 4.4	22,000
4.4 or more, but less than 4.7	23,000
4.7 or more, but less than 5.1	24,000
5.1 or more, but less than 5.4	25,000
5.4 or more, but less than 5.8	26,000
5.8 or more, but less than 6.4	27,000
6.4 or more, but less than 7.0	28,000
7.0 or more, but less than 7.6	29,000
7.6 or more, but less than 8.2	30,000
8.2 or more, but less than 8.8	31 ,000
8.8 or more, but less than 9.4	32,000
9.4 or more, but less than 10.0	33,000
10.0 or more, but less than 10.8	34,000
10.8 or more, but less than 11.6	35,000
11.6 or more, but less than 12.0	36,000
12.0 or more, but less than 12.5	37,000
12.5 or more, but less than 13.2	38,000
13.2 or more, but less than 14.0	39,000
14.0 or more, but less than 14.8	40,000
14.8 or more, but less than 15.2	41 ,000
15.2 or more, but less than 15.6	42,000
15.6 or more, but less than 16.0	43,000
16.0 or more	44,000

Load sharing

All rear axle sets must have a suspension system that provides effective damping and shares the load between the wheels of the set, so that no one tyre carries a mass more than 10 percent greater than the mass it would carry:

• if the load were divided so that each tyre carries an equal share of the load, or
• if the axle set is a tandem axle set containing a twin-tyred axle andlarge single-tyred axle (super single), and it is built to divide the load between the axles in the set in either a 60 percent 'twin'/40 percent 'large single' ratio or a 55 percent 'twin'/45 percent 'large single' ratio. A vehicle with this type of axle set requires an indelible plate to be fixed to the vehicle by the manufacturer (see Land Transport Rule: Vehicle Dimensions and Mass Rule 2002 for more information).

Non-steering axles

An axle that is fixed and does not steer.

Mass on front axles

In order to retain sufficient grip on the road surface when turning, it's recommended that buses and trucks have a minimum mass (weight) on their front axle(s). This mass shouldn't go below 20 percent (one-fifth) of the total mass on the axles of that vehicle. Drivers need to be aware of this at all times. The vehicle needs to be loaded in an appropriate way so this is achieved. Placing all the load behind the rear axles of the vehicle isn't recommended.

This recommendation has been introduced to make sure that vehicles with an increased rear overhang (which is now allowed) retain front traction and steering, and remain stable.

Heavy rigid vehicles first registered on or after 1 July 2002 must have at least 20 percent of their mass on the front axles at all times.

Retractable axles

Heavy rigid vehicles may have retractable axles in the rear axle set, provided:

• the retractable axle has an automated control to ensure that the axles remaining on the ground stay within the appropriate legal mass limits and manufacturer's limits, and
• forward distance and rear overhang limits are complied with when the axle is on the ground and when it is retracted (the position of the rear axis may change depending on whether the axle is retracted or touching the ground), and
• such retractable axles are certified for compliance with the requirements in both of the above points.

Note: only unladen vehicles can operate with an axle retracted.