Vehicle dimensions and mass

This page describes the legal requirements in the  Land Transport Rule: Vehicle Dimensions and Mass 2002 . It also includes information about subsequent relevant legislation. 

Read this page for general information and then choose among the other vehicle types below for your specific vehicle or combination. 

• Heavy rigid vehicles
• Light rigid vehicles
• Heavy trailers and vehicle combinations (full, semi, simple, pole, A- and B- train)
• Light trailers (light simple trailers)
• Static roll thresholds
• Heavy buses
• High productivity motor vehicles (HPMVs)

What are the general mass (weight) limits on New Zealand roads?

The words ‘mass’ and ‘weight’ are both used, but they mean the same thing. For example a vehicle’s tare (in kilograms) is its unladen mass, but you would measure it by using a weighbridge.

There are two different types of mass limit that apply to your vehicle and its load.

1. The limitation imposed by the vehicle’s design and construction. You must not exceed the vehicle ratings specified by the vehicle manufacturer for the chassis, axles, tyres and other components of the vehicle. For example, you are not allowed to load your vehicle above the specified maximum gross vehicle mass (GVM), gross combination mass (GCM), brake code mass (BCM) or tow a load greater than the drawbar is rated for.
2. Limits to axle mass are imposed to protect the road infrastructure. This is because certain sections of roads in New Zealand are not built to the same strength specifications as in other countries.

To find the operating gross mass (weight) of your vehicle, add the tare mass of the unladen vehicle to the mass of the load the vehicle is carrying. You must take into account any mass transferred to the rigid vehicle by an attached trailer. You can also measure this mass by using a weighbridge. This total mass must not exceed any of the vehicle’s design limits or the road limits.

Axles can have different types of tyres fitted to them, and the allowed mass changes depending on which type you are using.

	Single standard-tyred axle (includes two axles spaced less than 1 metre apart)
	Single large-tyred axle – tyres at least 330mm (13 inch) width by 24 inch diameter or 355mm (14 inch) width by 19.5 inch diameter (includes two axles spaced less than 1 metre apart).
	Twin-tyred axle.

The limits on the weight of vehicles on New Zealand roads and bridges have been introduced to protect roads that are designed and are maintained to a level called 'class 1'.

The limits on the weight of vehicles on New Zealand roads and bridges have been introduced to protect roads that are designed and are maintained to a level called 'class 1'.

Note: Some roads and bridges have lower weight limits than class 1. These lower limits have been imposed by the road controlling authority (RCA) to protect particular bridges or roads from damage. These special limits are indicated on road signs that read 'Class C' or 'Heavy vehicle axle limit' or 'Heavy vehicle bridge limits'. Only vehicles within the specified limits can use these roads or bridges.

For example, if you want to cross a bridge displaying the above sign, then an individual axle (not axle set) must not exceed 4300kg, each axle set must not exceed 50% of the axle set limits in the rule, and the vehicle must not travel over the bridge faster than 15km/h. Note that some of these signs will not have all three restrictions listed, for example if there is no speed listed, you can cross at the appropriate speed.

What is the minumum mass on front axles ?

In order to retain sufficient grip on the road surface when turning, your vehicle must have sufficient mass (weight) on the front axle(s). This mass shouldn’t be less than 20% (one fifth) of the total mass on the axles of the 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 the full load behind the rear axles of the vehicle isn't recommended.

This guidance has been introduced to make sure that vehicles with an increased rear overhang (which the Rule allows) retain front traction and steering and remain stable.

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

Drivers of vehicles that tow simple trailers (those with one axle set which aren’t semi-trailers) also need to be aware that the simple trailer can impose a large weight on the rear of the towing vehicle. This imposed weight can (by lever action through the chassis of the vehicle) reduce the effective mass bearing on the front axle(s) of the towing vehicle. Therefore simple trailers need to be loaded carefully so their load is distributed centrally over the axle(s) of the trailer. This will allow the towing vehicle to maintain front wheel traction.

Note:  There needs to be a small downward force on the tow coupling, to make sure a simple trailer remains stable while it's being towed. The downward force should be about 10% of the weight of the trailer and its load.

What is the trailer:truck mass ratio?

Heavy trailers have been identified as more likely to show stability problems than buses or trucks. For this reason the maximum mass on the axles of a heavy trailer is limited, and can't be more than 50% higher than the mass of the vehicle which tows it. Trailers within this limit are easier to control when braking and during emergency manoeuvres. This limitation on the mass of a heavy trailer applies at all times when heavy trailers are being moved in areas open to public access.

Mass ratio of towed vehicles

For a rigid vehicle (truck, tractor or ute) towing one heavy vehicle, the ratio of gross mass of the towed vehicle to gross mass of the towing vehicle must not exceed 1.5.

This requirement doesn’t apply if the speed of the combination vehicle is less than 40km/h, or the vehicle is operating under an overweight permit with a vehicle axle index above 1.1.

For a rigid vehicle towing two vehicles, the ratio of the gross mass of the rearmost vehicle to the total gross mass of the rigid vehicle and the first towed vehicle must not exceed 1.5.

Operators will need to ensure the vehicle that moves a loaded heavy trailer has sufficient mass for the purpose. It may be necessary to change loading practices so this can be achieved. This requirement mainly affects the movement of full and simple trailers. Semi-trailers and B-trains are less likely to be affected because part of the mass of these trailers is borne by the towing vehicle.

How do I assess stability by static roll threshold (SRT)?

The stability of vehicles can be greatly affected by the way they’re loaded. The load needs to be arranged so that its mass and height are appropriate for the design of the vehicle and type of load.

The static roll threshold (SRT) of a vehicle is a measure of the potential for that vehicle to roll over sideways. Vehicles with a low SRT are more likely to roll over than those with a higher SRT, especially when going around sharp bends and in sudden emergency maneuvers. That means the lower your SRT the less stable your vehicle is.

To improve their stability, heavy vehicles with a gross vehicle mass (GVM) greater than certain specified limits must meet or exceed a minimum static roll threshold value.

Trucks

The heaviest class of trucks (class NC with GVM over 12 tonnes) must meet a minimum SRT of 0.35g (where ‘g’ is the acceleration due to gravity). They aren't, however, required to be certified. 

Find out more about static roll thresholds

Trailers

If their load or body is over 2.8 metres high, the heaviest class of trailers (class TD, with GVM over 10 tonnes) will, in addition, need to be assessed for their tendency to roll over when loaded. This assessment is mandatory for all of these vehicles.

Trailers that don't meet the required level of stability will have their capacity to carry their existing load type reduced, or could be re-certified to carry a different type of load, or will need to be adjusted or modified to improve their stability.

Axle mass (weight) limits for standard vehicles

The following mass limits indicate the maximum mass (weight) allowed on class 1 roads.

There are three road-imposed legal mass limits that you must not exceed:

1. the individual axle limit, and
2. the axle set limit, and
3. the combined axle set limit, which depends on the distance from the first axle in any set to the last axle in any other set.

Note : As well as not exceeding an individual axle limit you must also meet the axle group limit. This means that you may not be able to load each axle to its maximum legal limit, because this could overload the axle set or group.

1: Individual axle limits

Single axle or axle set

(One axle or a dual axle of two axles less than 1 metre apart.)

2: Axle-set limits

Axle set mass limits are in place due to the concentration effect of having two axles close together. If each axle was loaded to the maximum allowed for it, excess road damage would result. Below are the possible combinations. Some axle sets do not have load sharing so a tolerance is allowed, which is why in some cases the axle set limit is less than the sum of the individual axle limits.

Tandem axle set

(Two axles spaced more than 1 metre but less than 2 metres apart)

Note : The 2 metres maximum does not apply to twin steer axle sets.

Tri-axle set

(Three axles spaced more than 2 metres but less than 3 metres apart.)

Quad axle set :

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

3: Combined axle-set limits

Maximum vehicle and axle mass (kilograms)

The total mass of a heavy vehicle or vehicle combination must be within the limits set out below, when the distance from any axle in any set is measured to any other axle in another set.

The table below gives the maximum allowed sum of the mass on any two or more axles that together do not constitute a single tandem axle set, a single tri-axle set or single quad-axle set, where the distance from the centre of the first axle to the centre of the last axle is 1.8 metres or more (including maximum gross weight).

Note: Vehicles can operate at higher mass on certain routes if on an HPMV permit .

What are the dimension limits for ‘standard’ vehicles?

The law states the maximum allowed width, height and other dimensions for vehicles to be allowed on New Zealand roads, which have been designed and built to accommodate these dimensions. If your vehicle fits within these dimensions it is called a standard-size vehicle.

All dimension limits are maximums, in metres (m) or millimetres (mm), unless otherwise stated. 

Summary table of dimension limits for rigid vehicles

A rigid vehicle has two axle sets, a driver’s position, a steering system, motive power and a single rigid chassis.

		Rigid vehicles
		Light vehicles		Heavy vehicles
		Not towing	Towing	Not towing	Towing
Maximum width		Two-wheeled vehicles (classes AA, AB, LA, LC): 1.0m All others: 2.5m
	Maximum height	4.25m
	Maximum forward distance	9.5m	8.5m	9.5m	8.5m
	Maximum rear overhang	4m from rear axis		With non-steering rearmost axle, the lesser of 4m from rear axis or 70% of foremost axle to rear axis. With steering rearmost axle, the lesser of 4.25m from rear axis or 70% of foremost axle to rear axis. A rigid bus that exceeds 12.6m in length, the lesser of 4.5m or 72% of wheelbase.
Maximum front overhang		3m ahead of front of driver’s seat when in its rearmost position (4m for an agricultural vehicle).
	Maximum overall length of vehicle	12.6m	11.5m	12.6m*	11.5m
Ground clearance		Light: No required minimum, but if light motor vehicles and trailers have their suspension modified so ground clearance is less than 100mm, then that suspension must be approved by a low volume vehicle certifier.
		Heavy: Minimum is the greater of 100mm OR 6% of the distance from the nearest axle to the point where the ground clearance is measured.
Maximum turning circle		25m diameter from wall to wall, excluding collapsible mirrors.
Maximum intervehicle spacing		N/A	4m	N/A	4m
Minimum SRT		N/A		0.35g (class NC only - over 12 tonnes GVM)
* Note: some buses can be longer.

Summary table of dimension limits for vehicle combinations

A combination vehicle is made up of a rigid vehicle towing another vehicle or vehicles.

		Trailers and vehicle combinations
		Trailer with one axle set			Trailer with two axle sets
		Semi	Simple	Pole	Full	Pole
Maximum width		2-wheeled vehicles (classes AA, AB, LA, LC); 1.0m All others: 2.5m
	Maximum height	4.25m
	Maximum forward distance (see  Heavy trailers and combinations for specific forward distance definitions, ie how they are measured)	9.2m  (previously 8.5m)	8.5m	8.5m with fully extended drawbar	8.5m	8.5m with fully extended drawbar
	Maximum rear overhang	Light: 4m from rear axis
		Heavy: Lesser of  4.3m  (previously 4.0m) from rear axis or 50% of forward distance except for class TC caravan trailer, they are the lesser of 4m or 65% of forward distance.	Lesser of 4m or 50% of tow coupling to rear axis		Lesser of 4m or 50% of front axis to rear axis
Maximum front overhang		2.04m radius arc ahead of centre of kingpin	2.04m radius arc ahead of centre of tow coupling	2.04m radius arc ahead of centre of turntable on tow vehicle	2.04m radius arc ahead of centre of turntable	2.04m radius arc ahead of centre of turntable on tow vehicle
	Maximum length of vehicle	N/A	12.5m (previously 11.5m)	11.5m excl. load	11.5m	11.5m excl. load
	Maximum overall vehicle combination length	19m  (previously 18m) or 18m if a quad with two steering axles.	22m (previously 20m)	20m (includes A-trains and B-trains and heavy rigid vehicles towing two trailers)
Ground clearance		Light: no required minimum, but if light motor vehicles and trailers have their suspension modified so ground clearance is less than 100mm, then that suspension must be approved by a low volume vehicle certifier.
		Heavy: minimum is the greater of 100mm or 6% of the distance from the nearest axle to the point where the ground clearance is measured.
Maximum turning circle		25m diameter from wall to wall, excluding collapsible mirrors
Intervehicle spacing		N/A	4m	N/A	4m max, 1m min ( Heavy trailers and combinations )	N/A
SRT		Light: N/A
		Heavy: (class TD only – over 10 tonnes GVM): 0.35g (those with load or body height over 2.8m above ground to be certified for SRT)

There are certain items that, for practicality, are allowed in addition to the maximum width and height limits for a vehicle. These are listed below.

What items are not included in determining the width of a vehicle?

The following items are not included in determining the width of a vehicle:

• side marker lamps and direction indicators
• collapsible mirrors that extend not more than 240mm beyond the side of the vehicle or its trailer
• ropes, lashings, straps, chains, and related connectors or tensioning devices that extend not more than 25mm from either side of the vehicle and are neither permanently nor rigidly fixed to the vehicle
• J-hook assemblies that extend not more than 25mm from either side of the vehicle, not more than 1.275 metres when measured from the vehicle's longitudinal centre-line, and that comply with the ratings specified on the manufacturer's plate affixed to the stockcrate or bin that is being secured
• central tyre inflation system hoses that extend not more than 75mm beyond the outside of the tyre on the drive axles of a heavy motor vehicle hubodometers that extend not more than 75mm beyond the 2.5 metres width limit from a non-lifting, non-steering axle
• whose outer casings are of a light colour, provided the hubodometer is fitted on the axle that causes the least overwidth
• cab exterior grabrails that extend not more than 50mm from either side of the vehicle
• the bulge towards the bottom of a tyre
• the wheels, on a rear-steering single large-tyred axle of a rigid vehicle, that extend not more than 25mm from either side of the vehicle.

What items are not included in determining the height of a vehicle?

Load-restraining devices, such as ropes, lashings, straps, chains, covers and related connectors and tensioning devices, that extend not more than 25mm above the body or load of the vehicle, and that are neither permanently nor rigidly fixed to the vehicle.

What are the limits for projecting loads?

Vehicles may carry loads which are higher, longer or wider than the dimensions of the vehicle itself, provided that the load doesn't exceed the maximum permitted dimensions for that class and type of vehicle, and the vehicle can be moved safely when loaded. It's the operator's responsibility to ensure the load is properly secured to the vehicle so that the vehicle remains stable at all times, and the load or parts of it cannot fall off.

Trucks towing full trailers can have an overhanging load up to 2.3 metres wide (1.15 metres each side of the centre line), extending over the 20 metres maximum vehicle length to a maximum of 22 metres.

There is a requirement for a certified rear underrun system (contact a specialist heavy vehicle certifier for details.) to be fitted if this overhang exceeds 1m, and the warning devices described below are still required. ( Find out more on our page on heavy vehicle full trailers .) Loads that overhang the outside of the body or deck of the vehicle by more than 1 metre to the front or rear, or more than 200mm to the left or right side, need to carry special warning devices attached to the overhanging end(s) of the load.

During the hours of daylight, there must be either:

• a clean white, or fluorescent red, orange or yellow flag, at least 400mm long by 300mm wide, or
• a frangible hazard warning panel (see diagram below).

Minimum dimensions of hazard warning panels, which can be used instead of flags on projecting loads

During the hours of darkness, the flags or hazard panels must be replaced with lights attached to the load as follows:

• For loads over 1 metre wide and extending more than 1 metre from the rear of the vehicle, one red lamp (facing toward the rear) on each side of load.
• For loads up to 1 metre wide and extending more than 1m from the rear of the vehicle, one red lamp (facing toward the rear) at the centre of load.
• For loads over 1 metre wide and extending from the front of the vehicle, one white or amber lamp (facing toward the front) on each side of load.
• For loads up to 1 metre wide and extending more than 1m from the front of the vehicle, one white or amber lamp (facing toward the front) at the centre of load.
• For loads extending more than 200mm beyond the side of the body of the vehicle, one red lamp (facing toward the rear) on each side of the load at the rear and one white or amber lamp (facing toward the front) on each side of the load at the front.

These lights need to be clearly visible in clear weather at a distance of at least 200 metres during the hours of darkness. This applies to all vehicles, regardless of when they were first registered.

Please note : goods service vehicles parked on a roadway must have a red light on the rear of the vehicle, or on the rear of projecting loads that extend more than 1.5 metres behind the vehicle.

General information about towing

Light vehicle towing

A light rigid vehicle (for example, a car or ute with a gross vehicle mass up to 3.5 tonnes) may only tow one vehicle. A light tractor, however, is allowed to tow two light vehicles at a speed not greater than 50km/h.

Towing a trailer and a motor vehicle

A heavy rigid vehicle can only tow both a trailer and an unpowered rigid vehicle if either:

• the rigid vehicle tows a semi-trailer, which tows an unpowered rigid vehicle, or
• the total gross mass of the combination is less than 20 tonnes and the rearmost vehicle is a light trailer or other light motor vehicle.

Towing two motor vehicles

A heavy rigid vehicle can only tow one unpowered heavy rigid vehicle.

A heavy rigid vehicle can tow two rigid vehicles without power only if:

• the gross mass of the combination is less than 20 tonnes, and
• the last vehicle is a light rigid vehicle, and
• at least one towing connection between consecutive vehicles is a rigid bar or A-frame.

Definitions and specifications

Axles

Single axle set means either one axle or two axles have their centres spaced less than 1 metre apart.

Tandem axle set means two axles have their centres spaced no less than 1 metre and no more than 2 metres apart.

Tri-axle set means there are three axles and:

• the centres of the first and third axles are spaced not less than 2 metres and not more than 3 metres apart, and
• all axles contain an equal number of tyres, and none of the axles is a single standard-tyred axle.

Twin-steer axle set means an axle set of two axles with single tyres, where both axles are connected to the same mechanism in order to steer similarly.

Quad-axle set means a set of four axles where:

• the centres of the first and fourth axles are spaced no less than 3.75 metres and no more than 4 metres apart, and
• all axles contain an equal number of tyres, and
• none of the tyres is a single standard tyre.

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 metres. Heavy rigid vehicles with a tow coupling are restricted to a maximum forward distance of 8.5 metres.

The forward distance for trailers is defined (measured) differently depending on the specific design (see  Heavy trailers and combinations ).

Ground clearance

Ground clearance is the distance from the ground to any part of the vehicle except for flexible mudflaps, wheels, tyres and devices designed to discharge static electricity.

Inter-vehicle spacing

The space between any two consecutive vehicles in a combination not including the drawbeam.

Oscillating axle

A pair of short axles in the same line across the vehicle, each axle being:

• mounted with two wheels on it (with each wheel at least 500mm apart across the vehicle), and
• able to oscillate, that is, one wheel can rise while the other falls.

Outside turning circle

A vehicle, including a combination truck and towed vehicle or vehicles, must be able to complete a 360 degree turn, both to the left and to the right, within a 25 metre diameter circle (wall to wall). The only projections which can be outside this circle are collapsible mirrors. No part of a vehicle in a combination, other than its tow coupling, may come into contact with another vehicle in the combination when performing this turn.

Overall length

The overall length of any combination of vehicles must not exceed 20 metres or 22 metres for a rigid vehicle and simple trailer combination or any combination with a rear full trailer carrying a reduced width load overhang utilizing a certified underrun system, see  Heavy trailers and combinations for details.

Rear axis

Rear axis (RA) is the point at which the vehicle rotates about during a turn. 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 a 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, 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 or two steering axles 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 retracting 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.

Quad-axle sets

If the vehicle has a quad-axle set with steering axles, the rear axis is as below:

Rear overhang

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

Speed of heavy vehicles without suspension

The maximum speed of heavy vehicles without springs or other effective cushioning suspension is limited to the lesser of 45km/h or the manufacturer's rating (typically the tyres will have a maximum allowable speed).

Speed of towing vehicles

Vehicles towing trailers (full, semi or simple) or other motor vehicles are limited to a maximum open road speed of 90km/h. Vehicles towing another vehicle without a rigid towing system are limited to 50km/h.

Drivers of these vehicles still need to obey lower speed limits set for particular roads.

Speed of tractors when towing

Tractors may not tow trailers at a speed exceeding 50km/h, unless the tractor meets all heavy motor vehicle requirements.

Wheelbase

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

Download Factsheet 13 – Vehicle dimensions and mass

Minimum dimensions of hazard warning panels, which can be used instead of flags on projecting loads

During the hours of darkness, the flags or hazard panels must be replaced with lights attached to the load as follows:

• For loads over 1 metre wide and extending more than 1 metre from the rear of the vehicle, one red lamp (facing toward the rear) on each side of load.
• For loads up to 1 metre wide and extending more than 1m from the rear of the vehicle, one red lamp (facing toward the rear) at the centre of load.
• For loads over 1 metre wide and extending from the front of the vehicle, one white or amber lamp (facing toward the front) on each side of load.
• For loads up to 1 metre wide and extending more than 1m from the front of the vehicle, one white or amber lamp (facing toward the front) at the centre of load.
• For loads extending more than 200mm beyond the side of the body of the vehicle, one red lamp (facing toward the rear) on each side of the load at the rear and one white or amber lamp (facing toward the front) on each side of the load at the front.

These lights need to be clearly visible in clear weather at a distance of at least 200 metres during the hours of darkness. This applies to all vehicles, regardless of when they were first registered.

Please note : goods service vehicles parked on a roadway must have a red light on the rear of the vehicle, or on the rear of projecting loads that extend more than 1.5 metres behind the vehicle.

General information about towing

Light vehicle towing

A light rigid vehicle (for example, a car or ute with a gross vehicle mass up to 3.5 tonnes) may only tow one vehicle. A light tractor, however, is allowed to tow two light vehicles at a speed not greater than 50km/h.

Towing a trailer and a motor vehicle

A heavy rigid vehicle can only tow both a trailer and an unpowered rigid vehicle if either:

• the rigid vehicle tows a semi-trailer, which tows an unpowered rigid vehicle, or
• the total gross mass of the combination is less than 20 tonnes and the rearmost vehicle is a light trailer or other light motor vehicle.

Towing two motor vehicles

A heavy rigid vehicle can only tow one unpowered heavy rigid vehicle.

A heavy rigid vehicle can tow two rigid vehicles without power only if:

• the gross mass of the combination is less than 20 tonnes, and
• the last vehicle is a light rigid vehicle, and
• at least one towing connection between consecutive vehicles is a rigid bar or A-frame.

Definitions and specifications

Axles

Single axle set means either one axle or two axles have their centres spaced less than 1 metre apart.

Tandem axle set means two axles have their centres spaced no less than 1 metre and no more than 2 metres apart.

Tri-axle set means there are three axles and:

• the centres of the first and third axles are spaced not less than 2 metres and not more than 3 metres apart, and
• all axles contain an equal number of tyres, and none of the axles is a single standard-tyred axle.

Twin-steer axle set means an axle set of two axles with single tyres, where both axles are connected to the same mechanism in order to steer similarly.

Quad-axle set means a set of four axles where:

• the centres of the first and fourth axles are spaced no less than 3.75 metres and no more than 4 metres apart, and
• all axles contain an equal number of tyres, and
• none of the tyres is a single standard tyre.

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 metres. Heavy rigid vehicles with a tow coupling are restricted to a maximum forward distance of 8.5 metres.

The forward distance for trailers is defined (measured) differently depending on the specific design (see  Heavy trailers and combinations ).

Ground clearance

Ground clearance is the distance from the ground to any part of the vehicle except for flexible mudflaps, wheels, tyres and devices designed to discharge static electricity.

Inter-vehicle spacing

The space between any two consecutive vehicles in a combination not including the drawbeam.

Oscillating axle

A pair of short axles in the same line across the vehicle, each axle being:

• mounted with two wheels on it (with each wheel at least 500mm apart across the vehicle), and
• able to oscillate, that is, one wheel can rise while the other falls.

Outside turning circle

A vehicle, including a combination truck and towed vehicle or vehicles, must be able to complete a 360 degree turn, both to the left and to the right, within a 25 metre diameter circle (wall to wall). The only projections which can be outside this circle are collapsible mirrors. No part of a vehicle in a combination, other than its tow coupling, may come into contact with another vehicle in the combination when performing this turn.

Overall length

The overall length of any combination of vehicles must not exceed 20 metres or 22 metres for a rigid vehicle and simple trailer combination or any combination with a rear full trailer carrying a reduced width load overhang utilizing a certified underrun system, see  Heavy trailers and combinations for details.

Rear axis

Rear axis (RA) is the point at which the vehicle rotates about during a turn. 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 a 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, 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 or two steering axles 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 retracting 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.

Quad-axle sets

If the vehicle has a quad-axle set with steering axles, the rear axis is as below:

Rear overhang

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

Speed of heavy vehicles without suspension

The maximum speed of heavy vehicles without springs or other effective cushioning suspension is limited to the lesser of 45km/h or the manufacturer's rating (typically the tyres will have a maximum allowable speed).

Speed of towing vehicles

Vehicles towing trailers (full, semi or simple) or other motor vehicles are limited to a maximum open road speed of 90km/h. Vehicles towing another vehicle without a rigid towing system are limited to 50km/h.

Drivers of these vehicles still need to obey lower speed limits set for particular roads.

Speed of tractors when towing

Tractors may not tow trailers at a speed exceeding 50km/h, unless the tractor meets all heavy motor vehicle requirements.

Wheelbase

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

Download Factsheet 13 – Vehicle dimensions and mass