How to choose tyres for your car: sizes, load rating, budget vs premium

Start with the numbers already on your car

Every tyre carries a size string on the sidewall, something like 225/45 R17 94Y. The first number is the tread width in millimetres, the second is the sidewall height as a percentage of that width, then the wheel diameter in inches. The 94 is the load index and the Y is the speed rating. The same string is printed on the sticker inside the driver's door shut or on the fuel flap, and that sticker is the one to trust if a previous owner fitted something unusual.

You can go up in load index or speed rating without problems. Going down is not worth the risk: an under-rated tyre flexes more under load, runs hotter and can fail at motorway speed. If your car is a heavier diesel estate or an EV, the extra weight is exactly why the manufacturer specified the higher rating.

Budget or premium: the per-mile maths

A budget tyre can cost half what a premium one does, but it usually wears faster and stops further from a standstill in the wet. Independent wet-braking tests regularly show a several-metre gap between the best and worst tyres in the same size, and that gap is roughly the difference between stopping and not stopping behind a lorry on a damp motorway.

The cheaper option also tends to need replacing sooner. If a budget tyre lasts 18,000 miles and a premium tyre lasts 30,000, the premium set often works out similar per mile while delivering shorter stopping distances for all of it. Mid-range brands are where most drivers should be looking: they usually carry a decent EU tyre label wet grip rating without the flagship price.

When a tyre actually needs replacing

• The legal UK minimum is 1.6mm across the central three-quarters of the tread, around the whole circumference.
• Wet performance drops off sharply below 3mm, so that is a sensible personal limit rather than the legal one.
• Cracking, bulges, or anything cut down to the cords means replace it now, regardless of tread depth.
• Uneven wear across the tread usually points to tracking or suspension, not the tyre itself.

Fit them in pairs, and put the better pair on the back

Match tyres across an axle: same size, same construction, ideally the same model. Mismatched grip left to right makes the car behave differently in each direction under braking. When you are replacing two of four, the newer pair goes on the rear axle. It sounds counter-intuitive on a front-wheel-drive car, but it is the rear losing grip that spins you, and the rear is the axle you cannot correct with the steering wheel.

Buying online and booking the fitting

Buying tyres online and paying a local garage to fit them is usually the cheapest route. Budget for fitting on top of the tyre price: valves, balancing and disposal of the old tyre are normally charged per wheel. Check the date code on the sidewall when the tyres arrive (four digits, week and year) — anything older than a couple of years has been sitting in a warehouse, even though it is still perfectly usable.

If your car has a space saver, a repair kit instead of a spare, or staggered wheels front to rear, write the sizes down before you shop. Staggered setups need two different sizes and cannot be rotated front to back.

Where to compare prices

Prices move week to week and stock differs by size, so check both retailers in the block above with your exact size in hand. If you are buying tyres because of an MOT advisory, our guide to MOT fail parts and costs covers what else a tester may have flagged, and our MOT legality checker tells you whether a modification is likely to be an issue at test.