The MOT Files

MOT defect file

Tyres of different sizes or construction on the same axle

Last updated

Quick answer

The two tyres on one axle are not the same size, or mix radial and cross-ply construction. Different makes and tread patterns side by side are legal in the UK; different sizes and structures are not.

Typical cost
£70–£280 per axle
DIY viability
Garage job
How to read a tyre sidewall size and service markingThe marking 205/55 R16 91V is separated into its six meanings: 205 millimetres section width, sidewall height equal to 55 percent of that width, radial construction, 16 inch rim diameter, load index 91 and speed symbol V. A separate DOT panel identifies the final four digits as the production week and year. Tyres on one axle must have compatible size and construction, and an inadequate load or speed rating is a defect.205/55 R16 91V205 — width, mm55 — height, % of widthR — radial construction16 — rim diameter, in91 — load indexV — speed ratingDOT … 2324week 23 · year 2024Date code sits on sidewallMatch axle specification · never downgrade load or speed rating
Read the full service description, not just the rim size. Tyres on the same axle must have compatible size and construction; a load or speed rating below the vehicle manufacturer’s requirement is a failure. The final four DOT digits give week and year of manufacture.

What you might notice

  • The car pulling gently to one side on a flat, level road with your hands relaxed
  • Different-looking sidewalls left and right: a taller profile, a wider tread, or a different rim diameter
  • Uneven wet grip, with one front wheel losing traction under acceleration before the other
  • Often invisible unless you crouch and read both sidewalls, which is exactly what the tester does

What causes it

  • An emergency replacement fitted from whatever the fitter had in stock, then never matched up
  • A previous owner replacing one tyre at a time and treating the size code as a rough guide
  • A space-saver spare left on the car after a puncture and quietly forgotten
  • A full set bought secondhand or part-worn, where the sizes were never checked against each other

Advisory or failure?

Tyres of different sizes fitted to the same axle, or of different structure — a radial on one side and a cross-ply on the other — is a major defect and a failure. Mixing radial and cross-ply is also prohibited outright by the Road Vehicles (Construction and Use) Regulations 1986, front to rear as well as across an axle. Where the mismatch is bad enough to affect steering or stability, the grading is dangerous. One point is worth being clear about, because it is widely misunderstood in Britain: different makes and different tread patterns on the same axle are legal here and are not a defect, provided the size and construction match. A space-saver spare in use is treated on its own terms — fitted within its speed and distance limits it is not a mismatch defect, and the spare itself is not part of the test.

Can you fix it yourself?

Garage job

Reading the sizes is a two-minute job you should do before the test rather than after it. The code on the sidewall runs width, aspect ratio, construction and rim diameter — 205/55 R16 — and both tyres on an axle must agree on all four, with R meaning radial. Fitting is machine work, so the tyre itself is not a driveway job. The trap when correcting it is buying only one tyre to match the odd one out: on an axle where the other tyre is already half worn, you end up with a grip imbalance that is legal but not much better, and on four-wheel-drive and many hybrids a rolling-radius difference across an axle also loads the transmission.

What it costs

Two matched budget tyres in a common size are £110 to £150 fitted; mid-range and premium pairs run £160 to £280. Larger rims, low-profile sizes and run-flats push past the top of the band on their own. Where only one tyre is at fault, the honest answer is often still to buy two, because pairing a new tyre with a nearly worn one across an axle leaves you with a different imbalance. Have the alignment checked at the same time if the wear pattern looks odd — £40 to £70 well spent on a car that has clearly had a haphazard tyre history.

What happens if you ignore it

Two different sizes on one axle mean two different contact patches and two different rolling radii, so braking force and grip are unequal at exactly the moment they need to match. On a driven axle the difference is fed continuously into the differential, and on a four-wheel-drive car that is a route to an expensive transfer case or coupling failure. The legal position is the same as any illegal tyre: up to £2,500 and three penalty points per tyre, and a mismatch is one of the easier things for a roadside check to spot.

Common questions

Can you have different tyres on the same axle?
Different makes and different tread patterns on the same axle are legal in the United Kingdom and are not an MOT defect, which is widely misunderstood here. What is not allowed is different sizes, or different construction, on one axle. That is a major defect and a failure.
Is it illegal to mix radial and cross-ply tyres?
Yes. Mixing radial and cross-ply construction is prohibited outright by the Road Vehicles (Construction and Use) Regulations 1986, front to rear as well as across a single axle. At the test it is a major defect, and it is graded dangerous where the mismatch is bad enough to affect steering or stability.
Can I drive with a space saver spare fitted?
Yes, within the speed and distance limits printed on the wheel, and a space saver in use is not treated as a mismatch defect. The spare itself is not part of the MOT at all. What catches people out is leaving it on the car for months after a puncture and forgetting it is there.
Do I have to replace tyres in pairs?
There is no legal requirement to, but when you are correcting a mismatch it is usually still the honest answer, because pairing one new tyre with a nearly worn one across an axle simply leaves a different imbalance. Two matched budget tyres are £110 to £150 fitted, with mid-range and premium pairs at £160 to £280.
How do I read the tyre size on the sidewall?
The code runs width, aspect ratio, construction and rim diameter, so 205/55 R16 means 205mm wide, a 55 per cent profile, radial construction and a 16 inch rim. Both tyres on an axle must agree on all four. It takes two minutes to crouch down and compare them, and it is worth doing before the test rather than after it.

Cars this happens to most

Of every model with at least 2,000 tests in the DVSA data, these record tyres of different sizes or construction on the same axle on the largest share of their MOTs. Across all of them the typical rate is 0.1% of tests.

  1. Volkswagen ID50.4%

    13 times in 2,914 tests

  2. Audi Q4 E-Tron0.4%

    41 times in 10,679 tests

  3. Smart (mcc) Forfour0.3%

    73 times in 22,245 tests

  4. BMW I40.2%

    16 times in 6,958 tests

  5. Volkswagen ID40.2%

    24 times in 11,285 tests

  6. Mercedes-Benz Eqc0.2%

    23 times in 12,524 tests

  7. Jaguar XE0.2%

    76 times in 42,718 tests

  8. BMW I30.2%

    40 times in 26,183 tests

A high rate here is a property of the fleet as much as the car: these models skew old, and almost everything fails more with age. It is a reason to check the item on a used example, not proof the model is badly built. Models with fewer than 2,000 tests are left out because a rate drawn from a few hundred cars moves too much to rank.

Pass rates for every make and model

Warning lights behind this

This defect is what a tester writes down. What you see from the driver’s seat is a symbol, and it is worth checking which one, because manufacturers reuse the same shape for more than one system.

This is general guidance, not a diagnosis. The severity DVSA records depends on the specific fault found, so the same item can appear as an advisory on one test and a failure on another. Ask a qualified tester or mechanic to inspect the vehicle.

Has this been recorded on your car?

Check the full MOT history for any UK registration.

Spaces are optional

Other common defects