Tyre faults that will fail an MOT
9 min readBy Wheel Fit
The short answer Tread below 1.6mm in the measured band is an automatic failure, but so are cuts, bulges, exposed cords, mismatched tyres across an axle and a badly seated tyre. Most are visible in a five-minute check you can do yourself.
What the tester checks
- Tread depth — at least 1.6mm across the central three-quarters of the tread, around the whole circumference. Measured at several points.
- Cuts and damage — any cut longer than 25mm or 10% of the section width, deep enough to reach the cords.
- Bulges, lumps or tears. Automatic failure. The casing has already failed — see sidewall damage and bulges.
- Exposed cords or ply anywhere.
- Tyre type mixing — radial and cross-ply mixed incorrectly, or different structures across an axle. See mixing tyre brands and patterns.
- Correct fitment — right size and load/speed rating for the vehicle, and directional tyres fitted the right way round.
- Seating on the rim, and whether the tyre fouls any part of the vehicle.
- Valve condition — damaged or badly leaning valves.
- TPMS on vehicles first used from 2012 — see the section below, because this one is widely misunderstood.
Defect categories, and what they mean for you
Since 2018 the MOT has graded defects rather than simply passing or failing them. It matters because two of the categories mean the car has failed and one does not.
| Category | Result | Typical tyre example |
|---|---|---|
| Dangerous | Fail — must not be driven away | Bulge, exposed cords, tread well below the limit |
| Major | Fail | Tread below 1.6mm, incorrect load or speed rating |
| Minor | Pass, recorded | Obviously under-inflated tyre on a TPMS-equipped car |
| Advisory | Pass, noted for attention | Tread close to the limit, early uneven wear |
A "dangerous" tyre defect is not just paperwork If a tyre is graded dangerous, driving the car away is an offence regardless of whether the old MOT is still valid. That is the situation where a mobile fitter is genuinely useful — the tyre can be replaced where the car stands.
The TPMS rule people get wrong
Malfunction, not low pressure The reason for rejection is a TPMS warning lamp indicating a system malfunction — not a lamp that is on because a tyre is genuinely low. If the light is on for low pressure, the system is working as designed. The check applies to M1 vehicles first used on or after 1 January 2012, and excludes motor caravans, ambulances and hearses over 2,500kg. Separately, an obviously under-inflated tyre on such a vehicle is recorded as a minor defect.
The practical advice is unchanged either way: set the pressures properly before the test, and get a malfunction light diagnosed rather than cleared. The TPMS warning light covers how to tell the two apart.
The ones people miss
Inner edge wear. Easily the most common surprise. You cannot see the inside shoulder without turning the wheels to full lock. Cars fail on inner edges that looked perfect from the outside. It is usually an alignment fault, so fixing the tyre without fixing the cause just buys you the same failure next year — uneven tyre wear.
The spare. Not tested on a normal car MOT, but worth checking while you are down there. A flat spare is worse than useless.
Directional tyres fitted backwards. Look for the rotation arrow on the sidewall. It happens more often than it should.
Load and speed rating below specification. Fitting a lower rating than the manufacturer specified is a failure and a genuine safety issue — load index and speed rating.
A five-minute pre-MOT check
- Turn the steering to full lock and look at the inner shoulder of both front tyres.
- Check tread in three places across each tyre — inner, middle, outer — using a gauge or a 20p.
- Run your hand around each sidewall feeling for bulges. Do it with the car stationary and cold.
- Check the valve caps are on and the valves are not perished or leaning.
- Roll the car forward half a turn and repeat the tread check — wear is not always even around the circumference.
- Set all four pressures to the door-plate figures — correct tyre pressure.
- Start the engine and confirm no TPMS light stays on.
Common questions
- Will worn tyres alone fail the MOT?
- Yes. Tread below 1.6mm in the measured band is a major defect, and each affected tyre is recorded separately.
- My tyres are at 2mm. Will they pass?
- Legally yes, and they will likely be advisoried. Whether that is a good idea is another question — wet performance falls off well above the legal limit. See how to tell if a tyre needs replacing.
- Can I drive away on a tyre marked dangerous?
- No. Have it replaced where the car is.
- Does the spare need to be legal?
- It is not part of a standard car MOT, but the moment you fit it, it is a tyre in use on the road and must comply.
- Are mismatched brands an MOT failure?
- Not by itself, provided sizes and structural types are compatible across each axle. See mixing tyre brands and patterns.
Sources
If you find a problem
Getting it fixed before the test is cheaper than a retest, and we can come to you rather than you driving somewhere on a tyre you already know is marginal. Call 07989 606060, or see mobile tyre fitting.
Related: tread depth and the law.
