The two tyres on one axle don't match in a way that matters — different sizes, different construction, or in some cases a significant mismatch in type. The two ends of an axle need to behave the same way under braking and cornering.
Wording as it commonly appears on an MOT certificate: “Tyres of different sizes, types or structures fitted to the same axle”.
What does it mean?
The two tyres on one axle don't match in a way that matters — different sizes, different construction, or in some cases a significant mismatch in type. The two ends of an axle need to behave the same way under braking and cornering.
How serious is it?
Usually recorded as: Major. The tester assesses the actual vehicle on the day, so your certificate is what counts.
What normally causes it?
- A single tyre replaced after a puncture with whatever was in stock
- A space-saver spare left on and forgotten about
- Second-hand wheels fitted with tyres already on them
What a mechanic would check
Read all four sidewalls and write down the size, load index, speed rating and construction. It's worth doing even when the car passes, because mismatches often creep in over years of one-tyre-at-a-time replacement.
What might need replacing
- A matching tyre for that axle
- Ideally a pair, if the existing one is well worn
Can you still drive it?
It's a failure. In practice, mismatched tyres change how the car behaves under emergency braking, which is the worst possible moment to discover it. Get the axle matched.
Repair cost
The cost of one tyre — or two if you want them matched for wear as well as spec. Note the tread depth of the tyre you're keeping before deciding.
Before the retest
Check every tyre, not just the one that failed — the legal minimum is 1.6mm across the central three-quarters of the tread, all the way round. Make sure tyres on the same axle match in size and construction, and that all wheel nuts or bolts are present and tight. Set pressures to the figure on the door shoulder or in the handbook the morning of the retest.
Retest rules
If the vehicle stays at the test centre for repair and is retested within 10 working days, a partial retest is often free; some items qualify for a free retest if you bring the car back by the end of the next working day. The exact conditions are set out on GOV.UK, so confirm with the test centre before you leave. A major or dangerous failure means the car cannot legally be driven away unless the previous MOT is still valid and nothing dangerous was recorded — check your certificate first.
Related help
More tyres and wheels failures · MOT failure decoder · Ask a mechanic about your certificate
This is general guidance from a UK mechanic, not a substitute for a physical inspection. Only the tester who inspected your vehicle can confirm what was recorded and why.