How to read a tire size: what 225/45 R18 95H means

Take 225/45 R18 95H. It is a tire 225 mm wide with a sidewall 45% as tall as it is wide, for an 18-inch wheel. It carries up to 690 kg at speeds up to 210 km/h. The sections below read the line in the order it appears on the tire.

Where to find the code

The line is molded into the sidewall next to the tire’s model name. The size and indexes always appear together, in the same order.

Width and profile height: 225/45

The first number, 225, is the tire width in millimeters, from one sidewall to the other. The second, 45, is the sidewall height as a percentage of that width. It runs from the rim to the tread: about 101 mm on this tire.

The smaller the second number, the lower the sidewall. A 225/45 tire has a lower sidewall than a 225/55 of the same width. It responds to the steering faster but rides harder, and a pothole hits the rim sooner.

Rim diameter: R18

R18 is the rim diameter: 18 inches. A tire marked R18 fits only an 18-inch wheel. The R itself stands for radial construction. Car tires sold today are radial, so the letter does not affect your choice.

Load index: 95

The number after the size is the load index. It is a code, not kilograms. It tells you the weight one tire can carry at the correct pressure. Index 95 means up to 690 kg.

Do not fit tires with a lower load index than your car maker specifies. An overloaded tire can fail, for example with a burst sidewall.

Speed index: H

The letter after the load index is the speed index: the highest speed the tire is rated for.

The speed index of new tires should not be lower than the one your car maker specifies.

XL, M+S and the snowflake

Next to the size you may find other marks. XL (Extra Load) marks a reinforced tire: at a higher pressure it carries more than a standard tire of the same size. M+S (mud and snow) is applied by the tire maker by its own criteria, with no standard winter test behind it. The three-peak mountain and snowflake symbol means the tire passed a standard winter traction test. If you drive on snow, look for it.

Date of manufacture

The date is at the end of the DOT code: the long string of letters and digits on the sidewall. Of the last four digits, the first two are the week and the last two the year.

Which size fits your car

A previous owner may have fitted a different size, so check the car maker’s data. It is in the owner’s manual and on a placard, most often in the driver’s door opening or on the fuel filler flap. Many cars have more than one approved size.

Kazakhstan’s rules forbid driving on tires whose size or load capacity does not match the vehicle model. Tires on one axle must share the same size, construction, model, and tread pattern.