8.2 Wheels, Tyres, Lights and Rear Marking Plates
Key Takeaways
The tyre requirement is at least 1.5 mm in principal grooves around the circumference across the prescribed tread band; it is not a requirement for every decorative shoulder groove.
Check tyre inflation, cuts, bulges, dual clearance, rim damage and the correct number and type of wheel fasteners.
Rear marking plates generally apply to motor vehicles above 12 t and trailers above 10 t GTM, with specified exemptions such as relevant urban route buses.
Check tyres for more than tread
Tyres provide the contact through which steering, braking and drive forces reach the road. A tyre with adequate tread can still be unsafe because of a bulge, exposed material, unsuitable rating or incorrect inflation. Inspect each tyre on every vehicle unit, including inner duals that are easy to overlook. A spare must also be suitable and secured.
The National Heavy Vehicle Inspection Manual describes the 1.5 mm minimum in principal grooves, in a continuous band around the circumference extending across at least 75% of tread width. Principal grooves include the main grooves with tread-wear indicators. Do not turn this into a demand that every shallow shoulder feature has 1.5 mm, but do inspect the whole tyre for damage and other rejection conditions.
Inflation, matching and damage
Use the manufacturer’s pressure guidance for the tyre, load and vehicle, and check using the appropriate conditions and equipment. Do not guess a universal truck pressure. Underinflation can increase flexing and heat; overinflation can affect contact and behaviour. A tyre that repeatedly loses pressure needs investigation rather than repeated inflation as a permanent fix.
Check cuts, bulges, exposed cords, uneven wear and foreign objects. Dual tyres must have appropriate clearance and compatibility so they do not rub or overload one tyre. Remove the vehicle from service or obtain assessment when unsafe damage is found. Do not crawl between wheels or disturb a loaded assembly without the safe procedure.
| Item | Look for | Why it matters |
|---|---|---|
| Tread | Principal-groove depth and uneven wear | Grip and signs of underlying faults |
| Sidewall | Cuts, bulges or exposed material | Potential structural failure |
| Dual pair | Contact, trapped objects and unsuitable matching | Heat, damage and uneven load sharing |
| Rim | Cracks, distortion or damage | Wheel integrity |
| Fasteners | Correct nuts/studs, looseness and rust trails | Wheel attachment |
| Valve and inflation | Leakage and correct pressure | Stable tyre operation |
Retreaded or regrooved tyres are not universally banned on every heavy vehicle steering axle. The actual standards, tyre markings, condition and operation determine suitability. Regrooving requires a tyre designed and marked for that purpose and the applicable standard. A driver should not cut grooves into an unsuitable tyre to make it appear compliant.
Wheel security
Wheels must have the correct number and type of nuts and studs and be properly attached. Cracked or bent rims require attention. Rust trails, movement marks or unusual fastener positions can be clues to looseness. Wheel-nut indicators are aids; their colour or angle is not a universal statutory inspection rule. An unchanged indicator does not prove every attachment is sound.
Follow the manufacturer’s and workshop’s tightening and recheck procedures. Do not use an improvised universal torque value or attempt unsafe work on split-rim or pressurised wheel assemblies. Such assemblies can be hazardous and require trained personnel and suitable equipment. Report vibration, unusual noise or steering changes promptly during the trip.
Lights and reflectors
Check high and low beam, indicators, stop lamps, tail lamps, clearance and marker lamps, number-plate illumination and any applicable reversing, fog or school warning lights. Required lamps and reflectors must work, be secure and have sound lenses. Cargo, dirt and accessories must not obscure them. Check the trailer as well as the truck.
Lights communicate the vehicle’s presence, width and intentions. A failed stop lamp can leave following traffic unaware of braking; a missing side marker can make a long trailer difficult to judge at night. Repair faults through the appropriate process rather than rely on hand signals for normal freight operation.
Flashing warning lights are restricted by colour, vehicle category and circumstances. Amber or yellow is associated with specified special-use warnings; red, blue and other emergency combinations have controlled uses. Fitting a beacon does not create emergency priority or make every roadside activity a 40 km/h scene. Verify that the vehicle and use are authorised, and maintain the required visibility.
Rear marking plates
Retroreflective rear marking plates help other road users recognise a heavy vehicle. The handbook generally requires them on motor vehicles above 12 t GVM and trailers above 10 t GTM, and describes additional combination situations. Specified exemptions include relevant route buses used only in urban areas. Check current Vehicle Standards Bulletin 12 for the exact vehicle, approved material, placement and replacement rules.
Keep plates clean, secure, visible and undamaged. Do not paint over them, obscure them with equipment or replace them with an unapproved decorative panel. Modern replacement requirements specify approved reflective classes; an obsolete plate illustration is not permission to fit any old material.
The DO NOT OVERTAKE TURNING VEHICLE sign concerns a qualifying vehicle at least 7.5 m long and its turning rules. Rear plates concern conspicuity and vehicle standards. One may incorporate the wording when suitable, but neither automatically supplies the legal effect of the other.
Key decisions
Inspect every tyre and wheel, confirm all required lights and markings, and use the correct standards for the actual vehicle. Visible accessories support safety only when properly fitted and maintained.
Official sources
NHVR Inspection Manual, wheels, tyres and hubs; Vehicle Standards Bulletin 12; handbook lights and plates. Sources checked 10 October 2026.
Which statement correctly describes the heavy vehicle tyre tread check?
Every decorative shoulder groove must be exactly 1.5 mm
Adequate tread makes bulges acceptable
Check at least 1.5 mm in the principal grooves within the prescribed continuous tread band, plus other damage and suitability requirements
Retreads are automatically prohibited on every steering axle
Sections you finish are checked off in the contents.