When to replace your car tyres safely

Why tyres deserve more of your attention in London

London is hard on rubber. You spend half your time braking and accelerating in stop-start traffic, half your time squeezing past kerbs on narrow residential streets, and a great deal of your time driving on wet surfaces where grip is already at a premium. Add in congestion, speed humps, potholes and the extra weight of an electric or hybrid car, and your tyres are working far harder than the odometer suggests.

A tyre is the only thing connecting you to the road. Four patches of rubber roughly the size of your palm carry everything — braking, steering, cornering. When they degrade, nothing else on the car can compensate. The good news is that tyres tell you how they are doing well before they fail, if you know what to look at. Ten minutes with a 20p coin and a pressure gauge every few weeks will keep you safe.

The legal limit — and why 3mm is your real marker

The UK legal minimum tread depth for cars is 1.6mm, measured across the central three-quarters of the tyre's breadth and around the whole circumference. Below that, you risk up to three penalty points and a fine per tyre. But legal is not the same as safe, particularly here.

Wet-weather testing consistently shows that braking distances climb sharply below 3mm, because a shallower tread pattern cannot clear water from under the contact patch quickly enough. On a greasy Blackwall Tunnel approach or a slick roundabout in the rain, that difference matters. Many drivers in the trade treat 3mm as the practical replacement point, and it is a sensible one for anyone doing regular London mileage. If you are heading into autumn or winter, replace at 3mm rather than squeezing out the last of the tread.

Checking tread depth yourself in five minutes

You do not need a workshop for this. You need five minutes and a coin.

• Insert a 20p coin into the main grooves. If the outer band of the coin is hidden by the tread, you have more than the legal minimum. If the band is visible, your tread is at or below the limit — book replacements.
• Check in at least three places around each tyre, and repeat across both edges and the centre. Tread wears unevenly, and a tyre can be legal on one edge and illegal on the other.
• Look for the moulded tread wear indicators — small raised bars set into the grooves at 1.6mm. If the tread is level with them, the tyre is finished.
• Do all four tyres, including the inner edge you cannot easily see. Turn the steering to full lock to expose it, or crouch down with a torch.
• Buy a cheap tread depth gauge if you prefer numbers. They cost less than a coffee and remove all guesswork.

Sidewalls: bulges, cracks and kerb damage

The sidewall takes the punishment that London kerbs dish out, and it cannot be repaired. Inspect it properly every time you check tread.

• Bulges or lumps — these mean the internal cords have broken. The tyre can fail without warning at speed. Replace it immediately; do not drive on it further than the nearest fitting centre.
• Cuts or splits deep enough to show cords — same verdict. It is scrap.
• Scuffing and grazing from kerbs is often cosmetic, but if the rubber has been gouged away deeply enough to expose the cord structure, replace.
• Perishing — fine cracks across the sidewall caused by sunlight, ozone and age. Light crazing is common on older tyres; deep, open cracks are a sign the rubber has hardened and lost grip.
• Bead damage where the tyre seats on the rim, often from driving on a soft tyre. This can cause slow leaks and should be assessed by a professional.

Uneven wear reveals what is actually wrong

The pattern of wear is diagnostic. Reading it can save you money and prevent you ruining a new set of tyres in a few thousand miles.

• Worn in the centre, edges fine — long-term overinflation. You are running on a narrower strip of tread than intended.
• Worn on both edges, centre fine — underinflation. Common in cars that sit for weeks between short London trips. Check pressures monthly, when the tyres are cold.
• Worn on one edge only — usually wheel alignment, sometimes camber. Get a four-wheel alignment check.
• Patchy, scalloped or cupped wear — worn suspension components, worn bushes or a balancing issue. New tyres will wear the same way until the underlying fault is fixed.
• Flat spots — often from heavy emergency braking or a seized brake caliper. Worth investigating rather than ignoring.

Uneven wear also means your tyres may be illegal before they look tired. A tyre with 4mm on the outside edge and 1.5mm on the inside is an MOT failure waiting to happen.

Age, repairs and choosing replacements

Rubber hardens with time, even when tread looks healthy. As a rule of thumb, replace tyres at six years old, and have anything over ten years inspected professionally. You can read the age from the four-digit date code on the sidewall: the first two digits are the week of manufacture, the last two the year. So 3423 means the 34th week of 2023.

Punctures in the central tread area can often be repaired to a proper standard if the hole is small enough and the tyre has not been run flat. Damage to the shoulder or sidewall cannot. Never accept a plugged repair on a sidewall, and be cautious with part-worn tyres generally — you rarely know their history, and the savings are small against the risk.

When you do replace, fit in pairs on the same axle and keep the newer, deeper-treaded pair on the rear, whether your car is front- or rear-wheel drive. It sounds counter-intuitive, but rear grip is what stops you spinning in the wet. Finally, check your pressures and torque the wheel nuts after 30 miles of driving, and check pressures again a week later. A new tyre that is quietly losing air through a poor seal is a problem you want to catch early.