Do I have to replace tyres in pairs, and where should new ones go?
When one new tyre is acceptable and when it is not, why new tyres belong on the rear whatever drives the car, and what four-wheel drive changes about all of this.
- Difficulty
- beginner
- Time
- 12 min
- Read
- 5 min
- Safety
- warning
Short answer
There is no law requiring tyres to be replaced in pairs, but the two on one axle should match in make, model, size and tread pattern, and they should be reasonably close in tread depth. If you are buying two, the new pair goes on the rear — on every car, including front-wheel drive — because losing grip at the back in the wet is far harder to catch than losing it at the front. Four-wheel drive is the exception, where an odd tyre can damage the drivetrain — check the handbook.
Two pieces of received wisdom collide here and one of them is wrong. The first is that new tyres go on the driven wheels, which for most people means the front. That sounds logical — that is where the power and most of the braking is — and it is precisely backwards. The second, that tyres must always be replaced in pairs, is a commercial habit rather than a rule. The reasoning behind the rear-axle guidance is worth understanding rather than just accepting: a car that understeers in the wet slows down, runs slightly wide and gives the driver time. A car that oversteers rotates, and most drivers cannot correct that. Every major tyre manufacturer and most driving organisations give the same advice for the same reason.
Safety
Step by step
- Decide whether one tyre will do.Replacing a single tyre is acceptable if the other one on the same axle is the same make, model and size, and has broadly similar tread depth. A brand new tyre next to one at 3 mm on the same axle gives noticeably different grip left and right in the wet, which is why fitters push back on it.
- Match make and model across the axle, always.Two tyres of the same size from different manufacturers have different compounds, different tread patterns and different wet performance. On the same axle that produces an imbalance under braking. Different tyres front to rear is much less of an issue, provided each axle is matched.
- Put the new pair on the rear.This applies to front-wheel drive, rear-wheel drive and everything else. The best tread goes on the back so that the rear of the car keeps grip in standing water and in an emergency swerve. Ask any fitter to do this; reputable ones do it as standard.
- Move the better existing pair backwards.If you have two half-worn tyres on the rear and are fitting two new ones, the correct arrangement is new on the rear and the old rears moved to the front. That gets the deepest tread where it protects you most.
- Check what four-wheel drive requires.This is the real exception. Many all-wheel-drive systems, and most with a mechanical centre differential, are damaged by significant differences in rolling circumference between axles. Some manufacturers specify that all four tyres are replaced together, or that a difference of more than a few millimetres of tread is unacceptable. Your handbook will say.
- Match the load and speed ratings the car specifies.The placard in the door shut or the fuel flap gives them. Fitting a lower load or speed rating than specified affects roadworthiness and can affect an insurance claim, and it is a false economy that costs very little to avoid.
- Think about rotation deliberately, not habitually.Rotating tyres front to rear evens out wear so all four wear out together, which is convenient and slightly cheaper. It also removes the diagnostic value of wear patterns and means you replace four at once rather than two. Some manufacturers recommend it, others do not, and directional or asymmetric tyres restrict how they can be moved. Check the handbook and the sidewall before doing it.
- Judge by tread depth, not by the legal minimum.The UK legal minimum is 1.6 mm across the central three-quarters of the tread around the whole circumference. Wet grip falls away well before that — most tyre manufacturers and safety organisations suggest replacing at around 3 mm. Treat 1.6 mm as the point at which you are committing an offence, not as a target.
Common mistakes
- Putting new tyres on the front of a front-wheel-drive car — It sounds right and it is the wrong way round. It creates a car that will spin its rear end in standing water, which is the failure mode drivers cannot recover.
- Mixing summer and winter tyres, or different constructions, on the same axle — The two sides of the axle then have different grip and different behaviour under braking, which is unpredictable exactly when it matters.
If it doesn't work
Fitter insists on selling two when you only need one
Cause: Either a genuine mismatch on the axle, or a sales habit — Fix: Ask them to measure the tread on the other tyre and tell you the difference. A small difference with the same make and model is fine; a large one, or a different tyre, is a legitimate reason.
You want the new tyres on the front and the fitter refuses
Cause: They are following manufacturer and industry guidance — Fix: They are right, and many will not do it. The rear-axle rule is about controllability in the wet, not about which wheels are driven.
Car has a different tyre size front and rear from the factory
Cause: Staggered fitment, common on performance and rear-drive cars — Fix: Then the rule becomes match each axle to its own specification. You cannot move tyres between axles at all on a staggered car.
One tyre is much newer than the other three on a four-wheel-drive car
Cause: A puncture replacement without checking the handbook — Fix: Ask a specialist to measure rolling circumferences. Some systems tolerate it, some do not, and the repair for a damaged transfer case or centre differential is expensive.
New tyres wear unevenly within a few thousand miles
Cause: Alignment out, or worn suspension components — Fix: Have the alignment checked before the new tyres are ruined too. The catalogue's tyre wear guide reads the pattern for you.
Questions people ask
Is it illegal to have different tyres on a car?
Different tyres on the front axle from the rear axle is legal, provided each axle is matched and all meet the vehicle's specification. Mixing tyres of different construction on the same axle — for example a radial and a cross-ply — is not permitted, and mixing different types across an axle is poor practice even where it is not specifically prohibited.
At what tread depth should I replace a tyre?
The legal minimum is 1.6 mm across the central three-quarters of the tread around the full circumference. Wet braking distances lengthen substantially below about 3 mm, which is why manufacturers and safety bodies commonly recommend replacing then rather than waiting for the legal limit.
Do I have to replace all four on a four-wheel-drive car?
Some manufacturers say yes; many specify a maximum permitted difference in tread depth or rolling circumference between axles. It is genuinely vehicle-specific and it is one of the few tyre questions where the handbook is the only reliable answer.