Not always. If one tyre is damaged and the other tyre on the same axle still has plenty of tread and is the same type, replacing just the damaged one is usually fine.
Replace both on the axle when:
- the tread depths would end up noticeably different
- the other tyre is worn or aged anyway
- your car is four-wheel drive and the manufacturer requires matching
- you can’t get a matching tyre for the remaining one
One rule isn’t optional: the two tyres on the same axle must be the same size and the same type of structure. UK regulations prohibit fitting tyres of different structure, such as radial and cross-ply, to the same axle.
Start here: a quick decision guide
1. Is the damaged tyre repairable?
If the puncture is in the central tread, under 6mm and the tyre is otherwise sound, a repair may avoid the question entirely. See what to do with a nail in your tyre.
2. How much tread is left on the other tyre on that axle?
Measure both. A tyre near the 1.6mm legal minimum is due for replacement soon anyway, so doing both at once often makes more sense.
3. Is your car four-wheel drive or all-wheel drive?
Check the handbook. Many require closely matched tread depths across all four tyres.
4. Can you get the same tyre model as the one you’re keeping?
If not, consider replacing both on that axle so the pair behaves consistently.
What must match on the same axle
| Requirement | Why |
|---|---|
| Same size (width, profile, rim diameter) | Different sizes change the rolling circumference and how the car handles |
| Same structure (radial or cross-ply) | Mixing structures on one axle is prohibited under UK regulations |
| Same type (run-flat or standard; winter or summer) | Different constructions and compounds behave differently under braking and cornering |
| Ideally the same model | Grip levels vary between tyre models, especially in the wet |
Load index and speed rating should meet or exceed the manufacturer’s specification on every tyre. See how to read a tyre sidewall.
The law on mixing
UK regulations set out which tyre structures can be combined. In practice, for a modern car with radial tyres all round, this rarely causes a problem. The points that matter:
- Tyres of different structure must not be fitted to the same axle.
- A car must not have cross-ply or bias-belted tyres on the rear axle with radial tyres on the front.
- Mixing tyre structures on the same axle is a major defect at MOT.
Mixing brands between the front axle and the rear axle is legal provided each pair matches and all four suit the car. It isn’t ideal, but it’s allowed.
Tread depth: how different is too different?
There’s no legal maximum difference between tyres on the same axle. The legal requirement is that every tyre has at least 1.6mm across the central three-quarters of the tread, all the way round.
In practice:
- A new tyre next to one close to the legal limit gives noticeably different grip on that axle, particularly in the wet.
- Many tyre manufacturers and safety organisations suggest replacing at around 3mm rather than waiting for 1.6mm, because wet braking falls away below that.
A reasonable approach: if the tyre you’d be keeping is at 3mm or below, replace both on that axle. If it still has most of its tread, replacing one is usually sensible.
See our uneven tyre wear patterns guide for what different wear patterns can indicate.
Should new tyres go on the front or the rear?
When you’re fitting two new tyres to a car, the usual advice is to put them on the rear axle and move the part-worn pair to the front. This applies whether the car is front or rear-wheel drive.
The reasoning: worn rear tyres lose grip in the wet before the fronts do, and a car that loses rear grip first is harder for most drivers to correct than one that understeers.
Check your vehicle handbook, since some manufacturers give their own guidance, and rotation patterns differ for directional and asymmetric tyres.
If you’re only replacing one tyre, it goes on the same axle as its partner. Ask the fitter whether shuffling the pairs across axles makes sense for your car.
Four-wheel drive and all-wheel drive
These vehicles need more care. In many AWD and 4×4 systems, tyres of noticeably different rolling circumference make the drivetrain work against itself, which over time can damage components such as the differential or transfer case.
Check the handbook for a maximum permitted difference in tread depth or circumference. Some manufacturers specify replacing all four tyres together, others allow axle pairs within a tolerance.
Tell the fitter your car is four-wheel drive when you call so the right number of tyres is brought out.
When replacing just one is the sensible choice
- The other tyre on that axle is nearly new and the same model
- The damage is unrelated to wear, such as a nail in the shoulder or kerb damage to the sidewall
- The car is two-wheel drive
- A matching tyre is available
Kerb or pothole damage often affects only one tyre, so a single replacement is common. See tyre bulges and sidewall damage.
When four makes sense
- All four are close to the wear limit or the same age
- Your car requires matched tyres across all four
- You’re switching type, for example from run-flats to standard tyres or to all-season tyres
- The tread is uneven across the car because of an alignment problem that’s now been fixed
Replacing four at once is more expensive up front, though many suppliers price multi-tyre orders more favourably. See what affects mobile tyre fitting costs.
What to check before you order
- The size code on the tyre you’re keeping, including load index and speed rating
- Tread depth of the other tyre on that axle
- Any markings such as XL, run-flat or a car-maker approval symbol
- Whether your car is four-wheel drive
- Which wheel position the damaged tyre is in
Our checklist before calling a mobile tyre fitter covers what else to have ready.
Frequently asked questions
Is it illegal to replace just one tyre?
No. There’s no requirement to replace tyres in pairs. What matters is that every tyre is legal and that the two on the same axle are the same size and structure.
Can I mix tyre brands on my car?
Between the front and rear axles, yes, as long as each pair matches and all four suit your car. On the same axle, tyres must be the same size and structure, and ideally the same model.
Should new tyres go on the front or back?
The usual advice is to fit new tyres to the rear axle and move the part-worn pair to the front, on both front and rear-wheel-drive cars, because worn rear tyres affect stability in the wet. Check your handbook for any manufacturer-specific guidance.
How different can the tread depths be on the same axle?
There’s no legal maximum difference. Every tyre must have at least 1.6mm across the central three-quarters. If the tyre you’d be keeping is around 3mm or less, replacing both usually makes more sense.
Do I have to replace all four tyres on a 4×4?
Sometimes. Many four-wheel-drive vehicles specify a maximum difference in tread depth or circumference to avoid stressing the drivetrain. Check your handbook.
Not sure how many tyres you need? Send us your tyre size and the tread depth of the other tyre, or call 07415955827 about mobile tyre replacement.