When to replace your tyres

Measuring tread depth properly

Use a tread depth gauge rather than a coin or your eye. Measure in the main grooves at the inner shoulder, the centre and the outer shoulder, then repeat at three or four points around the tyre. One part of the tread can still be within limits while another is already finished, and that contrast is often the most useful thing the measurement tells you.

Record the lowest reading, because that is the one that counts. If the inner edge is much more worn than the outer, or one tyre is far ahead of the rest, the depth is a symptom and something else needs attention.

It is worth measuring at the same time as you check pressures and keeping a note of the readings. Two or three sets of figures a few months apart show how quickly each tyre is wearing, which tells you when to budget for a replacement and whether one corner is wearing out of step with the rest.

Wear indicators and the 1.6 mm figure

Every tyre has tread wear indicators moulded into the bottom of the main grooves: small raised bars set at the minimum depth. When the surrounding tread wears level with those bars, the tyre has reached its limit. A small triangle, a TWI mark or a brand symbol on the shoulder points to where they are.

The minimum commonly written into law is 1.6 mm, but requirements vary by country and vehicle class, so check the rules that apply in Bahrain. Wet braking and resistance to aquaplaning fall away well before the bars are reached, which is why many tyre makers advise replacing at a greater depth if you often drive in rain.

• Measure with a gauge at several points across and around the tyre.
• Tread level with the wear bars means the tyre is finished.
• 1.6 mm is the commonly quoted legal minimum; confirm local requirements.

Age, and reading the DOT date code

The last four digits of the DOT code on the sidewall are the manufacturing date: the first two are the week, the last two the year, so 2425 means week 24 of 2025. That is the tyre's real age, which can differ from how long you have owned it.

Common guidance from tyre makers and motoring bodies is to have tyres inspected professionally from around five or six years old, and many makers advise replacement at around ten years from manufacture regardless of remaining tread. The figures differ between brands, so follow your tyre maker's guidance and your vehicle handbook. In a hot climate, treat the earlier end of that range seriously.

Age matters when you buy as well. A tyre that has spent a long time in storage has already begun to age, so it is reasonable to ask for the date code of the tyre being fitted to your car and how it has been stored. The same applies to a spare that has never touched the road.

Damage that ends a tyre's life

Some faults finish a tyre whatever the tread depth. A bulge or blister in the sidewall or tread means the internal structure has been damaged, and the tyre should not be driven on. Cuts that reach the cords, exposed or broken cords, and damage in the sidewall or shoulder are commonly not repairable.

Impact damage from a kerb or a deep pothole can harm the casing without leaving an obvious mark, and a tyre that repeatedly loses pressure has a fault to find rather than top up. After a hard hit, have the tyre and the rim checked.

• Bulges, blisters, exposed cords or deep cuts: stop using the tyre.
• Sidewall and shoulder damage is commonly not repairable.
• Repeated pressure loss is a fault to diagnose, not to top up.

Uneven wear patterns and what they suggest

Wear patterns are a readable record of pressure, geometry and suspension condition. They rarely prove one cause on their own, but they narrow the search a great deal.

Fitting a new set without dealing with the cause means the new tyres wear the same way. A Hunter 3D alignment measures the geometry, while a balance check deals with the rotating mass. Which of them you need depends on the wear pattern and on the symptom you can feel.

• Both shoulders worn more than the centre: commonly underinflation.
• Centre worn more than the shoulders: commonly overinflation.
• One shoulder only: often a camber or toe setting, or worn suspension parts.
• Feathered, sawtooth edges on the tread blocks: typically a toe problem.
• Cupping or scalloped dips around the tyre: often suspension wear or an unbalanced wheel.

Replacing in pairs, and which axle

Tyres are commonly replaced in pairs on the same axle so both sides have similar grip and diameter. A large difference in tread depth across an axle can affect braking stability and handling, and on some four-wheel-drive vehicles a mismatch in rolling circumference loads the drivetrain, which is why those handbooks sometimes require all four together.

When only two are being changed, common industry guidance on many cars is to fit the new pair to the rear axle, so the rear keeps the better wet grip and is less likely to lose stability first. Vehicle makers give their own instructions, so follow the handbook for your car. Check the spare too, including its date code, and remember a temporary spare has its own speed and distance limits.

If you would like a second opinion on tread, age or an odd wear pattern, the team at Wagon Wheel in Salmabad can measure the tyres, read the date codes and explain what the wear is pointing to.