How to tell if a tyre needs replacing
7 min readBy Wheel Fit
The short answer Tread depth is only one of the reasons to replace a tyre, and it is the one people check last. Age, damage, wear pattern and repair history all end a tyre's life too. A tyre can be entirely legal and still be finished.
It is worth separating three things that often get muddled: what is illegal, what is unsafe, and what is simply past its useful life. They are not the same threshold, and only the first one carries a fine.
The ten-point check
All of this can be done on a driveway in about five minutes, with the car cold and on level ground.
- Tread depth across the width. Check the middle and both shoulders, not just the easiest spot. The legal minimum is 1.6mm across the central three-quarters — tread depth and UK law.
- Tread wear indicators. The raised bars in the grooves sit at 1.6mm. If the tread is level with them, the tyre is at the legal limit.
- Wear evenness. One shoulder gone, or the centre worn, points at a cause you need to fix — uneven tyre wear.
- Age. Find the four-digit DOT code — week and year of manufacture. How long tyres last explains where it is.
- Sidewall condition. Any bulge, deep cut or exposed cord means replace now — sidewall damage and bulges.
- Cracking. Fine crazing is age; deep cracks mean the rubber has perished.
- Embedded objects. Nails, screws, stones wedged deep in the grooves.
- Pressure retention. Does this tyre need topping up more than the others? Why a tyre keeps losing pressure.
- Vibration or noise that has appeared recently — often balance, sometimes a deforming tyre.
- Repair history. A tyre with several previous repairs, or one repaired near an earlier repair, may not be repairable again.
The thresholds, side by side
| Tread depth | Status | Basis |
|---|---|---|
| Below 1.6mm | Illegal | UK law — up to £2,500 and 3 points per tyre |
| 1.6–2mm | Legal, wet performance falling away | Independent testing and road safety guidance |
| ~3mm | Common recommended change point | Widely advised as best practice, particularly for winter |
| New | Typically around 8mm | Varies by tyre and pattern |
Legal requirement vs recommendation 1.6mm is the law. Changing at 3mm is a widely-held recommendation based on wet braking performance, not a legal requirement — anyone telling you 3mm is "the legal limit" is wrong. We think it is good advice; we are not going to dress it up as law.
Replace regardless of tread if
- There is a bulge, lump or exposed cord anywhere on the tyre.
- There is a cut or tear deep enough to reach the cords.
- The damage is in the sidewall or shoulder — not repairable wherever it is.
- The tyre has been run flat, even briefly — the internal structure will have been damaged.
- The tyre is badly perished, with deep cracking.
- The tread is worn into the belts anywhere, even in one small patch.
Age: the reason low-mileage cars catch people out
Rubber degrades whether or not the tyre is used. A tyre that has spent eight years doing 2,000 miles a year can have 6mm of tread and still be unfit, because the compound has hardened and the sidewalls have perished.
This bites hardest on caravans, trailers, classics, motorhomes and second cars. It is also the reason to check the date on any tyre you are buying — a "new" tyre that has sat in a warehouse for five years has already used part of its life.
Is it worth repairing instead?
Frequently, yes. A repairable puncture costs a fraction of a new tyre and keeps a known tyre on the car. The repairable area is narrower than most people expect, though — see can a puncture be repaired?
If the tyre was already close to the end on tread or age, replacing is usually the better spend even when a repair is technically possible.
Common questions
- Does the 20p test actually work?
- As a rough screen, yes — the outer band of a 20p is close to the legal minimum, so if you can see the band the tyre is worth measuring properly. It is an indicator, not a measurement; a proper depth gauge costs very little.
- My tyres passed the MOT last month. Am I fine for a year?
- No. An MOT is a snapshot. A tyre at 2mm at test time can be below the limit within a few thousand miles — see tyre faults that fail an MOT.
- Do I have to replace them in pairs?
- Not always. Replacing all four or just one covers when it genuinely matters.
- How often should I check?
- Monthly, along with pressures, and before any long journey. It takes a couple of minutes — see correct tyre pressure.
If a tyre is due
We fit replacements at your home or workplace, so a borderline tyre can be changed on the driveway rather than on a trip you would rather not make. Call 07989 606060 or see mobile tyre fitting.
