Factsheet 13a – September 2005

Heavy rigid vehicles

This factsheet describes the maximum dimensions and weights for heavy rigid vehicles.

Heavy rigid vehicles include heavy trucks, buses, heavy mobile homes, mobile cranes, fire engines, heavy forklifts, heavy tractors, heavy self-powered agricultural and construction machines and vehicles with pivot steering.

A rigid vehicle has two axle sets, a driver's position, a steering system, motive power and a single rigid chassis. A small range of special vehicles with one registration plate, and a chassis split into two dependent parts and connected by means of a permanent steering pivot, are also rigid vehicles.

Read about the special requirements for articulated buses.

Heavy rigid vehicles are those with a maximum gross vehicle mass (GVM, usually specified by the manufacturer) over 3500 kilograms (kg).

Omnibus classes MD3, MD4 and ME, goods vehicle classes NB and NC, and any other powered rigid vehicle with a GVM over 3500 kg are included.

• Note: You find the gross mass of a vehicle by adding the tare mass of the unladen vehicle to the mass of the load the vehicle is carrying. Also include any weight transferred to the rigid vehicle by an attached trailer.

Dimension requirements

Vehicles (including their load) with dimensions greater than those set out below are classed as overdimension vehicles. For more information see Factsheet 53, Overdimension vehicles and loads or contact the Overdimension Permit Issuing Agency on 0800 OVERSIZE (0800 683 774).

Width

The maximum width (including any load) is 2.5 metres (m), or 1.25 m 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 (mm) each side for collapsible mirrors
• 25 mm each side for ropes, lashings, straps, chains, connectors and tensioning devices that aren't permanently or rigidly fixed to the vehicle, or J-hooks (to secure stock crates or bins)
• 75 mm each side of drive axles only, for the air hoses of central tyre inflation systems
• 75 mm for hubodometers on a non-lifting, non-steering axle that causes the least over-width
• 50 mm for exterior grab rails on the cab (to help the driver and passengers get in and out safely)
• trolley bus poles and their safety cables when they are collecting electric power from an overhead conducting wire. Ground clearance of the poles must be at least 2.5 m when they swing outside the body line of the bus.

Overall length (excluding collapsible mirrors)

The maximum length (including load) is 12.6 m. When they are towing a trailer or other motor vehicle, the maximum length for heavy rigid vehicles (including the load) is 11.5 m. (See the appropriate trailer factsheet in the factsheet 13 series for the overall length of a particular combination vehicle.)

Height (including load)

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

The height of the body or load of class NC trucks (goods service vehicles with a GVM over 12 tonnes) or their operating gross mass may be restricted by stability requirements, particularly the need for the vehicle to have a minimum static roll threshold (SRT). See Factsheet 13e, Static roll thresholds for more information on static roll thresholds.

Don't include trolley bus poles, when they're extended to collect power from an overhead conducting wire, in the determination of the height of a trolley bus.

Determining the rear axis (RA)

If the vehicle has only one non-steering axle, the RA is at the centre of that axle.

If the vehicle has a tandem axle set with only non-steering axles in its rear axle set and each axle has an equal number of tyres on it, the RA is midway between the centres of the axles.

If the vehicle has tandem axle set with only non-steering axles in its rear axle set and one axle has twice as many tyres on it as the other axle, the RA is positioned two thirds of the distance from the lesser tyred axle towards the greater tyred axle.

If the vehicle has a non-steering triaxle set in its rear axle set, then the RA is midway between the extreme axles of the set.

If the vehicle has one steering axle in its rear set, together with one non-steering axle, the RA is at the non-steering axle.

If the vehicle has one steering axle in its rear set, together with two non-steering axles, the RA is midway between the extreme non-steering axles of the set.

If the vehicle has one or more retracted axles in its rear set, together with one or more non-retracted axles, the RA is midway between the extreme non-retracted axles of the set.

Forward distance

Forward distance, for a rigid vehicle, means 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 m. Heavy rigid vehicles with a tow coupling are restricted to a maximum forward distance of 8.5 m.

Rear overhang

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

• For a heavy rigid vehicle whose rearmost axle is a non-steering axle, the maximum rear overhang is the lesser of 4 m or 70 percent of the wheelbase ('A' in the diagram)

• For a heavy rigid vehicle whose rearmost is a steering axle, the maximum rear overhang is the lesser of 4.25 m or 70 percent of wheelbase. (In the diagram, the rear axis is at the centrepoint of the non-steering axle or axles.)

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

Front overhang

The 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 m.

Ground clearance

The minimum ground clearance is 100 mm. The ground clearance must also be at least 6 percent of the distance from the nearest axle to the point where the ground clearance is measured (except when loading or unloading). Items not included in the ground clearance requirement are: flexible mudflaps, wheels, tyres and devices designed to discharge static electricity.

Outside turning circle

A vehicle (including projections) must be able to complete a 360 degree turn, both to the left and to the right, within a circle with a wall-to-wall diameter of 25 m. The only projections which can be outside this circle are collapsible mirrors.

Permitted axle sets

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

• single axle set, which may steer, 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, centres spaced less than 1 m apart.

Tandem axle set means two axles, centres spaced no less than one and no more than 2 m apart.

Tri-axle set means three axles, where the centres of the first and third axles are spaced no less than two 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.

Rear steering axles

Forklifts may have a rear steering axle. Their rear axis is at the non-steering axle (usually the front axle).

Heavy rigid vehicles with a coupling for towing a heavy trailer must not have a rear steering axle.

Heavy rigid vehicles may have steering axles in the rear axle set if not more than half the axles in the rear set steer at any one time. Note that the rear axis is at the centrepoint of the non-steering axles in the rear axle set. Rear overhang and forward distance requirements must be met by vehicles with rear steering axles.

Heavy rigid vehicles with rear steering axles may only tow one light trailer.

Some mobile cranes can allow all axles to steer at very low speeds in an off-road location. For travel on a road, at least one of the axles must be locked so its wheels are parallel with the longitudinal centre line of the vehicle.

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 tyre carries a mass more than 10 percent greater than the mass it would carry:

• if all the tyres in the set were the same width and the load was shared equally between the tyres, or
• if a tandem axle set contained a twin-tyred axle and large single-tyred axle ('super single') and was built to divide the load between the tyres in the set in either the 60 percent twin/40 percent large single ratio or 55 percent twin/45 percent large single ratio. (A vehicle with these axle sets must have an indelible plate fixed to it by the manufacturer – see the Vehicle Dimensions and Mass Rule.)

Read about the speed of unsprung vehicles.

Retractable axles

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

• 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
• 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.)
• such retractable axles are certified for compliance with the requirements in both of the above points.

Please note that only unladen vehicles can operate with an axle retracted (but a tractor unit with a retracted rear axle can tow an unladen semi-trailer).

Mass on front axles

It is recommended that a heavy rigid vehicle has, at all times, at least 20 percent of its gross mass on the front axle or twin-steer axle set of the vehicle. This gives the front wheels enough grip on the road to steer the vehicle.

Heavy rigid vehicles first registered on or after 1 July 2002 must have 20 percent of their mass on their front axle(s) at all times.

Stability of heavy rigid vehicles

Most class NC trucks (goods service vehicles with a maximum gross mass exceeding 12 tonnes) must have a static roll threshold, when laden, of at least 0.35 g (where g is the acceleration due to gravity). For more information see Factsheet 13e.

Omnibuses of classes MD3, MD4, and ME (with a gross vehicle mass greater than 3.5 tonnes) must comply with the stability requirements in the Passenger Service Vehicles Rule (Rule 31001, 1999).

Tow coupling position

For towing a light full or light simple trailer: The coupling position can be at the rear of the vehicle, provided the maximum rear overhang, forward distance and overall length limits are not exceeded.

For towing a heavy full trailer: The coupling must be no further behind the rear axis of the truck than 40 percent of the wheelbase of the truck. The wheelbase is measured from the rear axis of the truck to the foremost axle of the truck.

For towing a heavy simple trailer (including Stinger Steer Transporters): The coupling must be at least 700 mm rearward of the rear axis of the truck and at a distance of not more than 50 percent of the wheelbase of the truck.

• Note: For Stinger Steer Transporters, 'tow coupling' includes an articulated fifth wheel attachment with a kingpin, or a ball attachment.

For towing a semi-trailer (excluding Stinger Steer Transporters):

• For a rigid vehicle with one axle in its rear set, the coupling position must not be behind the centre of that axle.
• For a rigid vehicle with two or three axles in its rear set, the coupling position must not be more than 300 mm behind the rear axis of the towing vehicle.

Projecting loads

Factsheet 13, Vehicle dimensions and mass describes the hazard warning devices you need to attach to projecting loads within the maximum dimensions allowed for a heavy rigid vehicle. The requirements for overdimension vehicles and loads are explained in Factsheet 53.

Maximum speed

Heavy rigid vehicles and articulated buses are limited to a maximum open road speed of 90 km/h. They still need to obey lower speed limits set on particular roads.

School buses are limited to a maximum speed of 80 km/h.

Heavy rigid vehicles without springs or effective cushioning suspensions (eg some agricultural and construction machines) are limited to a maximum speed of 45 km/h.

Towing

See Factsheet 13c, Towing and trailers (full, semi, simple, pole, A- and B-train) for information about towing trailers and other vehicles.

Articulated buses

Articulated buses have a driver's seat, a steering system, motive power and two rigid sections that articulate relative to each other. They have interconnecting compartments that allow passengers to move between them and are permanently coupled together.

Articulated buses have three axle sets and have special requirements, as follows:

• Overall length: 18 m.
• Rear axis position: Both front and rear sections of the bus have a rear axis. If the axle supporting the rear section is a steering axle, the NZ Transport Agency (NZTA) will determine the position of the rear axis of the rear section.
• Forward distance: 8.5 m (both front and rear sections). The forward distance of the rear section is the distance from the rear axis of the rear section to the articulation point.
• Rear overhang: The lesser of 4 m or 50 percent of the forward distance of the rear section.
• Articulation point: Not further behind the rear axis of the front section than a distance equal to 40 percent of the wheelbase of the front section.
• Turning circle: For a 360 degree turn, the maximum outside diameter is 25 m. The minimum inside radius is 5.3 m.

Where you can find out more

See:

• Land Transport Rule 41001 Vehicle Dimensions and Mass 2002.
• Land Transport Rule 41001/1 Vehicle Dimensions and Mass Amendment 2005.
• Land Transport (Road User) Rule 2004 (61001) (PDF, 200 KB).
• Land Transport Rule 31001 Passenger Service Vehicles 1999.

You can also contact the NZTA:

• Email us: info@nzta.govt.nz.
• Phone our contact centre: 0800 699 000.
• Write to us: NZ Transport Agency, Private Bag 6995, Wellington 6141.