Mixing Tyres: The Rules on Sizes & Types

There are firm rules about mixing tyres, some of them law and some strong safety practice. They exist because a car handles predictably only when the tyres are working consistently, especially the two on the same axle.

What the law says

UK law is clearest on construction. It is illegal to fit tyres of different construction, radial and cross-ply, on the same axle. It is also illegal to run radial tyres on the front axle with cross-ply on the rear; if the two are ever mixed front to back, the radials must be on the rear.

In practice this rarely bites, because almost every modern car tyre is radial and cross-ply has all but disappeared from mainstream sizes, but the law remains, and matters for classic vehicles. Tyres across an axle should also match in size, and obviously mismatched sizes on one axle can fail an MOT.

Same construction, different brand

Fitting tyres of the same construction and size but different brands or patterns across an axle is not in itself illegal. It is, however, not recommended by tyre makers. Different brands use different compounds and tread designs, so grip and behaviour differ from side to side, which can show up as uneven handling, particularly in the wet. For consistent results, identical tyres in matching pairs per axle are the sensible standard, and buying a matching pair, the two ordered together online from Tyres.co.uk, keeps grip even across the axle.

New tyres to the rear

When only two tyres are replaced, the newer pair belongs on the rear axle, regardless of whether the car is front- or rear-wheel drive. The reasoning is stability: better grip at the rear keeps the back of the car planted, where a rear that lets go first is much harder to control than understeer at the front. It is a point that surprises front-wheel-drive drivers, but it is the settled advice.

Categories and condition

Different tyre categories should not be mixed, and never across an axle. Summer, winter, all-season, run-flat and on or off-road tyres each behave differently, so combining them undermines the consistency the car relies on. The same caution applies to badly mismatched wear, and to directional tyres, which must also be fitted the correct way round. Some 4x4 makers go further and specify a maximum tread-depth difference between axles, so the handbook is worth checking.

One exception is the temporary-use spare, which is allowed to differ while in use, provided its speed limit, usually 50mph, is observed until a proper tyre is refitted.

From the workshop: the cross-ply rule is mostly history now, but the everyday version still holds, match tyres across each axle and put the newer pair on the back. We see cars pulling under braking because someone fitted one odd tyre, and on a wet road that is exactly when it bites.

Sources and accuracy. The mixing rules here, including the radial and cross-ply law and the new-tyres-to-the-rear guidance, reflect UK regulations and trade advice at the time of writing. Anything safety-critical should be confirmed against current official guidance and the vehicle handbook. If anything here looks wrong, get in touch and we will check it and put it right.