Inspect the full working surface
The manual requires the light-vehicle tread pattern to be visible across the width and around the entire circumference, with at least 1 mm depth. Do not judge the whole tyre by one deep groove. Turn or reposition the vehicle safely to inspect the portion initially against the ground, and check for uneven wear.
Tread is only one condition. Damage, exposed structure or an unsuitable tyre can make a vehicle unsafe despite a measured groove. Follow the tyre and vehicle manufacturer’s permitted load and pressure requirements; do not treat the legal minimum tread as an ideal condition for rain.
Motorcycle tread and retreads
For a motorcycle with engine capacity exceeding 50 cc, the manual requires a visible pattern across the tread and around its circumference with at least 1 mm depth. At 50 cc or below, a pneumatic tyre must show a visible pattern over at least 80% of the full tread width at every position around it.
A motorcycle may not be fitted with a retreaded tyre. A tyre that looks usable on another vehicle is not automatically lawful on a motorcycle. Match the tyre to the vehicle and maintain it before riding.
Wear indicators and tyre damage
The tyre regulation confirms the manual’s 50 cc motorcycle boundary. For a tyre subject to the ordinary pneumatic-tyre rule, it is also prohibited to use a tyre whose tread is level with a fitted tread-depth indicator. Do not rely only on a 1 mm reading elsewhere. The regulation excepts a motorcycle of at most 50 cc and a trailer drawn by a tractor at no more than 40 km/h from that particular paragraph; it does not exempt them from dangerous-condition rules.
Do not use a tyre with exposed cord, broken fabric, a structure-related lump or bulge, or a condition that may endanger people or damage the road. The regulation additionally controls deep cuts reaching cords, regrooving and tyres for operating-licence passenger vehicles. A defect is not harmless simply because air remains in the tyre.
- A cord-depth external cut exceeding 25 mm or 10% of maximum tyre width, whichever is greater, is prohibited.
- A regrooved tyre with bead diameter of 430 mm or less is prohibited.
- Operating-licence minibuses, midibuses and buses require the prescribed commercial steel radial tyres.
Worked situation
Most of a car tyre has deep grooves, but the inner edge is worn smooth around the tyre. Checking only the centre groove misses the defect. The manual’s full-width and full-circumference requirement means that one good measurement is insufficient.