Your tyres are the only part of your car in contact with the road, which makes tread depth a critical safety factor. UK law sets a minimum tread depth for cars, and driving below it risks a fine of up to £2,500 per tyre and three penalty points — plus significantly increased stopping distances in wet conditions. This guide explains the legal requirement, how to check your tread at home, and when to book a replacement.
The Legal Minimum Tread Depth in the UK
For cars, light vans, and light trailers, the legal minimum tread depth in the UK is 1.6 mm across the central three-quarters of the tyre, around its entire circumference. New tyres come with approximately 8 mm of tread, so the usable range before replacement is around 6.4 mm.
The penalty for driving with illegal tyres is serious: up to £2,500 and 3 penalty points per tyre. A car with four illegal tyres could result in a £10,000 fine and 12 penalty points — enough to revoke a licence. Your insurance may also be invalidated in the event of an accident if your tyres are found to be below the legal limit.
Many tyre safety experts and manufacturers recommend replacing tyres at 3 mm rather than waiting for the legal minimum. At 1.6 mm, wet braking distances can be up to 44% longer than at 3 mm.
How to Check Tyre Tread Depth: The 20p Coin Test
The easiest way to check whether your tyres are approaching the legal limit is the 20p coin test:
- Insert a 20p coin into the main tread grooves of your tyre.
- If the outer band of the coin (which is 1.6 mm wide) disappears into the groove, your tread is above the legal limit.
- If you can see the outer band of the coin, your tread may be at or below 1.6 mm — book an inspection immediately.
Check multiple points around the circumference and across the width of each tyre, as tyres can wear unevenly. You can also buy a purpose-made tread depth gauge from a motor factor for around £5, which gives a precise measurement in millimetres.
Understanding Tyre Wear Patterns
How your tyres wear can reveal underlying issues with your car:
- Even wear across the tread: Normal. The tyre is wearing as expected.
- Wear on both outer edges, fine in the middle: Under-inflation. The tyre is running soft and the sidewalls are bearing the load.
- Wear only in the centre: Over-inflation. The tyre is over-pressured and only the centre is in contact with the road.
- Wear on one edge only: Wheel alignment or suspension issue. The wheel is not sitting at the correct angle.
- Patchy or scalloped wear: Often caused by worn shock absorbers causing the wheel to bounce on the road surface.
Uneven wear shortens tyre life and can indicate a more expensive underlying problem. A garage can inspect your tyres and advise on whether a wheel alignment or suspension check is needed.
When and How to Replace Tyres
Replace tyres when tread depth reaches 3 mm (or immediately if it reaches 1.6 mm). Also replace any tyre that shows bulges, cuts, or sidewall damage, regardless of tread depth — these defects can cause a blowout.
Tyres should also be considered for replacement based on age: most manufacturers recommend replacing tyres that are more than 5–6 years old, even if the tread looks acceptable. Rubber degrades over time, particularly if the car is parked in direct sunlight. The manufacture date is embossed on the tyre sidewall as a four-digit code (e.g. 2319 = 23rd week of 2019).
When replacing tyres, it is best practice to fit two identical new tyres on the same axle. Mixing tyre brands or types on the same axle can cause uneven handling, particularly in wet conditions.