Tyres and vehicle safety checks: legal tread depth and what the theory test asks
Updated •5 min read
Cars, light vans and light trailers must have a tread depth of at least 1.6 mm across the central three-quarters of the tyre and around its whole circumference. The Highway Code gives this in Annex 6, and it is the number theory test questions are most likely to ask.
What the Highway Code says about tyres
Annex 6 covers vehicle maintenance, safety and security (Highway Code: Annex 6). On tyres it says:
| Vehicle | Minimum tread depth |
|---|---|
| Cars, light vans and light trailers | 1.6 mm across the central three-quarters of the tread, around the entire circumference |
| Motorcycles, large vehicles and passenger-carrying vehicles | 1 mm across three-quarters of the tread, in a continuous band around the entire circumference |
| Mopeds | Should have visible tread |
Tyres must also be correctly inflated to the vehicle manufacturer's specification for the load being carried, and should be free from certain cuts and other defects. Annex 6 tells you to refer to the vehicle's handbook or data for the right figure, so this guide does not give pressures. Check your own vehicle's handbook.
Tyre pressure checks
Annex 6 says to check tyre pressures weekly, before your journey, when the tyres are cold. Warm or hot tyres may give a misleading reading. It also says under-inflated or over-inflated tyres adversely affect your brakes and steering.
Excessive or uneven tyre wear may be caused by faults in the braking or suspension systems, or by wheels that are out of alignment. Have these faults corrected as soon as possible.
If a tyre bursts while you are driving, try to keep control of the vehicle. Grip the steering wheel firmly and allow the vehicle to roll to a stop at the side of the road. If you have a flat tyre, stop as soon as it is safe, and change it only if you can do so without putting yourself or others at risk. Otherwise call a breakdown service.
Tyre age
Annex 6 sets a rule on tyres over 10 years old. They must not be used on the front axles of goods vehicles over 3.5 tonnes maximum gross weight, or passenger vehicles with more than 8 passenger seats. For cars, the point to know is that tread depth and condition are the checks that apply to you.
Penalty points for defective tyres
Defective vehicle condition can lead to penalty points. Gov.uk lists endorsement code CU30, "using a vehicle with defective tyre(s)", at 3 penalty points (gov.uk: penalty points (endorsements)). Annex 6 itself warns that some vehicle defects can attract penalty points. New drivers should note that 6 points in 2 years means revocation.
Other safety checks in Annex 6
Annex 6 also tells you to take special care that lights, brakes, steering, exhaust system, seat belts, demisters, wipers, washers and audible warnings all work. It adds that:
- lights, indicators, reflectors and number plates must be kept clean and clear;
- windscreens and windows must be kept clean and free from obstructions to vision;
- lights must be properly adjusted to prevent dazzling other road users, especially when the vehicle is heavily loaded;
- fluid levels should be checked at least weekly, and low brake fluid may result in brake failure;
- before winter, the battery should be well maintained and there should be anti-freeze in the radiator and windscreen bottle;
- you should understand every warning display on the instrument panel, and not ignore a warning that comes on while driving.
If your vehicle pulls to one side when braking, Annex 6 says it is most likely a brake fault or incorrectly inflated tyres, and you should consult a garage or mechanic immediately.
How the theory test asks about it
Typical questions ask for the legal minimum tread depth, how often to check pressures and when (cold, before a journey), what causes uneven wear, and what to do after a burst tyre. Others ask what a warning light means or why a vehicle pulls to one side. In wet conditions, tyre grip links to stopping distances and bad weather driving.
Practise
See rule pages on the Highway Code, then try a practice test. The free theorytest.ai diagnostic shows which topics need work. theorytest.ai is independent and is not affiliated with the DVSA.
Frequently asked questions
What is the legal tread depth for a car?
At least 1.6 mm across the central three-quarters of the tread and around the whole circumference (Highway Code Annex 6).
How often should you check tyre pressures?
Weekly, before a journey, when the tyres are cold, according to Annex 6.
What should tyre pressure be?
Annex 6 says to inflate to the manufacturer's specification for the load. Check your vehicle's handbook.
What do you do if a tyre bursts?
Keep control, grip the wheel firmly and let the vehicle roll to a stop at the side of the road.
Can bad tyres give you penalty points?
Yes. Gov.uk lists code CU30, using a vehicle with defective tyres, at 3 penalty points.