Tyre tread depth
The legal minimum for cars is 1.6 mm across the central three-quarters, all the way round.
Tread is what gives water somewhere to go. On a dry road a bald tyre grips well; in rain it has nothing to clear the water with, which is why tread depth and wet-weather stopping are the same subject.
The legal minimum for a car is 1.6 mm, measured across the central three-quarters of the tyre and around its entire circumference — so a tyre worn below the limit in one band fails even if the rest looks fine. Larger vehicle classes have their own requirements, and the figure for them is not the same, which is worth knowing if you are revising for the lorry or bus test.
It is a minimum rather than a recommendation. Wet grip falls off well before 1.6 mm, so replacing earlier is a reasonable decision rather than an over-cautious one. Uneven wear across a tyre is also a symptom worth chasing — it usually points at pressures or alignment.
12 practice questions on this
Each one shows the answer, and our note on why every other option is not it.
Car
- How would under-inflated tyres affect your vehicle? Safety and your vehicle
- When would you increase the pressure in your tyres so that it's above the normal value? Vehicle loading
- What's the legal minimum tread depth for tyres on your trailer or caravan? Safety and your vehicle
- What’s the minimum depth of tread on the tyres of a trailer? Vehicle loading
Lorry & Bus (LGV/PCV)
- What's the minimum depth of tread required over three-quarters of the breadth of a lorry tyre? Vehicle condition
- What would be illegal? Vehicle condition
- Why are brushes fitted to this vehicle's wheel arch? The road
- What's most likely to cause a burst tyre? Vehicle condition
- On your daily walkaround check, you see that one front tyre is more than 10 years old. What should you do before using the vehicle? Vehicle condition
- What should you regularly check on the tyres of your bus? Vehicle condition
Driving Instructor (ADI Part 1)
- Tyres on cars, light vans and trailers must have a continuous tread depth of at least 1.6 mm. How much of the tyre must have this depth of tread? Band 3 driving test, disabilities, law
- What’s the minimum legal depth of tread on the tyres of a trailer? Band 2 traffic signs and signals, car control, pedestrians, mechanical knowledge