Key takeaways
- Replace tyres once tread nears 1.6mm — most safety bodies advise acting at around 3mm because wet grip falls off sharply below that.
- A bulge in the sidewall means internal damage; the tyre can fail without warning and should be replaced straight away.
- Cracking, vibration, repeated punctures, uneven wear and age are all signs a tyre is past its best.
- A tyre over about 10 years old should be replaced regardless of tread, even if it looks barely used.
Tyres are the only part of your car touching the road, so knowing when they are worn out is one of the most useful safety skills a driver can have. Some signs are obvious, like a bulge or smooth tread; others are easy to miss until they cause a problem. Here are the seven clearest signs it is time for replacements.
How do you know when tyres need replacing?
You know tyres need replacing when the tread is low, the rubber is cracked or bulging, you feel new vibration, wear is uneven, punctures keep happening, or the tyres are simply old. Any one of these can make a tyre unsafe. The headline check is tread depth, but the other six matter just as much for your safety.
1. The tread is getting low
Low tread is the most common reason to replace a tyre. The UK legal minimum is 1.6mm across the central three-quarters, but most manufacturers and safety bodies recommend replacing at around 3mm, because wet braking and aquaplaning resistance fall away noticeably below that. The quickest home check is the 20p test.
If the outer band of a 20p coin is hidden when you push it into a main groove, you are likely above the limit. If you can see the band, the tread is low. For the full method, see our guide on checking tread depth, linked at the end.
2. There is a bulge in the sidewall
A bulge or blister on the sidewall is one of the most serious signs of all. It means the internal structure has been damaged, often from a pothole or kerb impact, and the tyre can blow out without warning at speed. A bulged tyre should be replaced immediately and is not repairable.
3. You can see cracks in the rubber
Fine cracks across the tread grooves or in the sidewall mean the rubber is perishing. This happens with age and exposure to sunlight, heat and ozone, and it weakens the tyre even if the tread looks fine. Deep or widespread cracking, sometimes called crazing, is a clear sign the tyre needs replacing.
Cracking is especially common on cars that cover few miles or sit unused for long periods, where the rubber ages faster than the tread wears. A caravan or second car can perish long before the tread runs out.
4. You feel a new vibration
A vibration through the steering wheel or seat that was not there before can point to a tyre problem. It may be a wheel that needs balancing, but it can also signal internal damage, a flat spot, or uneven wear. New, unexplained vibration always deserves a check rather than being driven through.
If the vibration appeared after hitting a pothole or kerb, suspect impact damage. Balancing may cure a mild wobble, but if a tyre is damaged inside, replacement is the only safe option.
5. The tyre keeps losing air or puncturing
An occasional puncture is bad luck; repeated air loss is a warning. A tyre that needs topping up often may have a slow puncture, a perished valve or a corroded rim. If a puncture is outside the repairable central area, or the tyre has already been repaired more than the maker allows, it needs replacing.
Repairs are only permitted within the central three-quarters of the tread, per BS AU 159, and there are limits on how many repairs a single tyre may have. Beyond that, a new tyre is the safe choice.
6. The wear is uneven across the tread
Tyres should wear evenly. Heavier wear on one edge usually means the wheel alignment is out; wear in the centre or both edges points to over or under-inflation. Patchy or scalloped wear can indicate worn suspension. Uneven wear shortens tyre life and can leave part of the tyre below the legal limit while the rest looks fine.
Reading the wear pattern can tell you what is wrong before you spend on new tyres, so the underlying fault does not ruin the replacements too.
7. The tyres are simply old
Even with good tread, tyres age. Rubber hardens and loses grip over time, and most manufacturers advise replacing tyres at 10 years old regardless of wear, with checks from around 5 years. You can read a tyre's age from the four-digit DOT date code on the sidewall, which gives the week and year of manufacture.
Spotted one of these signs?
If you have spotted any of these, do not gamble on the next journey. Our guide on how to check your tyre tread depth shows the full method, and what your wear patterns tell you helps you find the cause. When it is time for new rubber, Fast Tyre brings mobile tyre fitting to your home, work or the roadside across London and central England, usually within 30–60 minutes.
Frequently asked questions
Legally you can use a tyre to 1.6mm, but most manufacturers and safety bodies advise replacing at around 3mm. Wet braking and resistance to aquaplaning fall off sharply below 3mm, so replacing earlier keeps you safer and avoids dropping below the legal limit between checks.
No. A bulge means the internal structure is damaged and the tyre can fail suddenly. Sidewall damage is not repairable under BS AU 159, which only allows repairs within the central three-quarters of the tread. A bulged tyre must be replaced straight away.
Yes. Rubber hardens and perishes with age, losing grip even with plenty of tread. Most makers recommend replacing tyres at 10 years and checking them from around 5 years. The four-digit DOT code on the sidewall tells you the week and year of manufacture.
A new vibration often means a wheel needs balancing, but it can also signal a flat spot, uneven wear or internal tyre damage, especially after hitting a pothole. Balancing may fix a mild wobble, but a damaged tyre needs replacing, so have it checked rather than ignored.
You can replace a single tyre, but it is usually best to replace tyres in pairs across an axle so grip is balanced left to right. A fitter can advise based on how worn the other tyres are and which axle is affected.
Wear on one edge usually points to wheel alignment being out; centre or both-edge wear points to incorrect pressure. Patchy wear can mean worn suspension. Fixing the underlying cause matters, otherwise the same fault will wear out your new tyres too.