The 1.6 mm rule: what it applies to
For passenger vehicles with up to eight passenger seats, light goods vehicles within the stated weight category and light trailers first used on or after 3 January 1933, the regulations require at least 1.6 mm of tread across a continuous band comprising the central three-quarters of the tread and around the entire outer circumference. [1]
That wording matters. The rule is not simply one reading at one point on the tyre, and it is not a generic rule for every vehicle type. Larger or different vehicle categories can have different statutory requirements.
- Check more than one point around the circumference and across the relevant tread area.
- Use the vehicle’s category and manufacturer information where the vehicle is not a typical passenger car, light van or light trailer.
- Do not treat the tyre sidewall’s maximum-pressure figure as the vehicle’s required operating pressure.
A tyre can fail the condition test even with visible tread
The road-use regulations also cover tyres that are unsuitable for use, insufficiently inflated for the vehicle’s use, have a qualifying cut reaching ply or cord, a structural lump, bulge or tear, exposed ply or cord, or another defect that makes the tyre unfit for use. [1]
This is why tread alone is not a complete roadworthiness check. A bulge, a deep cut, exposed structure or pressure loss should be assessed on its own evidence rather than treated as ordinary wear.
Part-worn tyres have a separate supply standard
A part-worn tyre may be supplied only if the separate safety regulations are met. The original tread grooves must have at least 2 mm depth across the full breadth of the tread and around the full outer circumference. The tyre must also meet conditions covering structural defects, inflation testing, repairs and required markings. [2]
For a non-retreaded part-worn tyre in the stated categories, the regulations require the relevant approval mark and permanent, legible “PART-WORN” marking in uppercase letters at least 4 mm high. [2] A second-hand tyre that looks usable is not enough; the supply rules are specific.
- Separate the 2 mm part-worn supply standard from the 1.6 mm in-service road-use minimum for the common passenger/light-vehicle category.
- Check for marking, visible structural condition and the appropriate explanation of the tyre’s suitability before deciding.
- Use the Part-Worn Tyres route for the Mitcham workshop discussion; use New Tyres where a replacement tyre is the more appropriate option.
An MOT certificate is not a continuing roadworthiness guarantee
The registered keeper remains responsible for keeping a vehicle safe to drive. GOV.UK makes clear that a vehicle can be unsafe even with a current MOT certificate, which is why a newly noticed tyre defect should not wait for the next test date. [3]
The Department for Transport has stated that a driver stopped with illegal tyres could receive a £2,500 fine and three penalty points per tyre. [4] Enforcement outcomes depend on the circumstances; this guide does not treat penalties as legal advice or a substitute for checking the current law.
What to do when you are uncertain
IQ Tyres’ confirmed free tyre safety check looks at overall tyre condition and tread depth. Cracked tyres are a recurring finding. The suitable next route depends on the issue found: it may be maintenance, puncture assessment or tyre replacement.
Use this legal guide to understand the rule, but use the relevant practical route to act on the tyre itself. Do not rely on a legal minimum alone to decide that a visibly damaged or pressure-losing tyre is suitable to keep using.