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.
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.