Every tyre carries a small block of code on its sidewall, and most drivers walk straight past it. That code is not decoration. It tells you the tyre's size, how much weight it can carry, how fast it is rated to go, and roughly how old it is. Learning to read it takes about two minutes, and it can stop you buying the wrong tyre, running an unsafe one, or being talked into a replacement you do not need.
Start with the size
The most prominent marking looks something like 205/55 R16. Read it in three parts. The first number, 205, is the tyre's width in millimetres, measured from one sidewall to the other. The second number, 55, is the aspect ratio: the height of the sidewall expressed as a percentage of the width. A lower number means a shorter, stiffer sidewall and usually sharper handling; a higher number means a taller sidewall and a softer ride. The R stands for radial construction, which is standard on virtually every modern car tyre, and the final number, 16, is the diameter of the wheel rim in inches that the tyre fits.
Getting this string exactly right matters. A tyre that is the wrong size may rub against the wheel arch, throw your speedometer reading off, or in the worst case not seat properly on the rim at all. Your car's correct size is listed in the owner's manual and usually on a sticker inside the driver's door frame or fuel filler flap. If you are ever unsure, that sticker beats any guess.
Load index and speed rating
Immediately after the size you will see a number and a letter, for example 91V. The number is the load index, a code for the maximum weight each tyre can carry. A load index of 91, for instance, corresponds to 615 kg per tyre. You do not need to memorise the table, but you do need to respect it: fitting tyres with a lower load index than your car requires means each tyre is carrying more than it was designed for, which builds heat and raises the risk of failure.
The letter is the speed rating, the maximum speed the tyre is designed to sustain. V means 149 mph, H means 130 mph, T means 118 mph. Most UK drivers will never approach these speeds, but the rating is still a useful proxy for the tyre's construction and heat tolerance. As with load index, never fit a tyre rated below what your car manufacturer specifies.
The age code
Tyres age even when they are not being used, as the rubber compound slowly hardens. The date of manufacture is stamped in a small oval on the sidewall, usually starting with the letters DOT followed by a four-digit code. The first two digits are the week of manufacture and the last two are the year, so 2224 means the tyre was made in the twenty-second week of 2024. There is no legal maximum age for car tyres in the UK, but as a rule of thumb, tyres older than five or six years deserve a close inspection for cracking, and any tyre approaching ten years old should be replaced regardless of how much tread is left. If you are buying a used car, checking these four digits on all four tyres takes seconds and tells you a lot about how the car has been maintained.
Tread wear, traction and temperature
You may also see three ratings grouped together: treadwear, traction and temperature. Treadwear is a comparative number, not a mileage promise — a tyre rated 400 should last roughly twice as long as one rated 200 under the same test conditions. Traction is graded from AA down to C and describes wet grip in a straight-line braking test, while temperature, graded from A to C, describes how well the tyre resists heat build-up. These grades are a helpful comparison tool when choosing between two tyres, but they are no substitute for checking your actual tread depth. The UK legal minimum is 1.6 mm across the central three-quarters of the tread, and safety organisations recommend replacing tyres at 3 mm, because wet grip drops off sharply below that point.
What to check before you buy
Before ordering any tyre, run through this short checklist. First, confirm the full size code against your door sticker or manual. Second, check that the load index and speed rating meet or exceed the manufacturer's specification. Third, read the four-digit date code so you know you are not paying full price for old stock. Fourth, look at the tread wear indicators, the small raised bars inside the main grooves, which sit flush with the tread surface when the tyre reaches the legal minimum. And finally, inspect the sidewalls for cuts, bulges or cracking, any of which means the tyre should come off the car regardless of tread depth.
A surprising number of tyre problems start with a simple mismatch: the wrong size, a lower load rating, or a tyre that has quietly aged past its best. Reading the sidewall puts that information in your hands before you spend anything. If you do spot a problem, a mobile tyre fitting service can check the tyre at your home or workplace and replace it without a trip to a garage, which is worth knowing when a bulge or a flat leaves you unable to drive safely.
Two minutes spent reading a sidewall is one of the cheapest safety checks in motoring. It will not make you a tyre expert, but it will make you a much harder driver to sell the wrong tyre to.
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