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What Do Tyre Markings Mean?

By: Kevin Watson MSc - Updated: 28 Oct 2012 | comments*Discuss
 
Tyre Width Load Capacity Speed Markings

Check the sidewall of a vehicle’s tyre. There’s the maker’s name, the type of tyre, the country of manufacture and perhaps a short description of the tyre such as ‘tubeless steel belted radial’. There’s also a sequence of numbers and letters. This sequence confirms the size of the tyre and other details. It also verifies that the tyre meets European and UK standards for tyre safety.

Width

The best way of explaining these markings is to take a common example. Consider a standard tyre on a mid-range saloon. This may read: 205/55R16 91H. The first of the numbers is 205. This refers to the width of the tyre in millimetres. The tyre is therefore 205 mm wide.

Aspect Ratio

The next number is 55. This is a percentage. The industry calls this percentage the aspect ratio of the tyre. The ratio is the height of the sidewall compared to the width of the tyre. With a 55 tyre, therefore, the height of the sidewall is 55% of the tyre’s width.

Radial

The next marking is R. This is fairly common and stands for radial. Radial tyres date back to 1915 when the inventor and tyre maker Arthur W. Savage took out a patent for the design. A radial tyre has cords that run along it. These cords are usually polyester, aramid or steel. They help to give the tyre its strength and longevity. There are also cords that run across the tyre from one edge to the other.

Diameter

After ‘R’, a tyre has another number. This is the diameter of the inner rim of the tyre. But unlike the first number, which is in metric millimetres, the measurement is in inches. In the example above, the tyre has an inner rim diameter of 16 inches.

Load Capacity

The next number gives the load capacity of the tyre. To establish the capacity, it’s necessary to refer to a load index chart. A tyre with a load index number of 91 can cope with a maximum weight of 615 kg. The load index numbers range from 65 to 108. At the lower end, a 65 tyre can bear a weight of 290 kg. At the other, a 108 tyre can handle a maximum weight of 1000 kg.

Speed Symbol

The final symbol in the sequence of numbers and letters gives the maximum speed for the tyre. This maximum speed assumes a full load. The full load is the carrying capacity of the tyre as given in the load index and indicated by the previous number.

‘H’ refers to a maximum speed of 131 mph. A tyre with a 91H marking can therefore safely reach 131 mph with a full load of 615 kg.

The speed symbols are not in a logical order. They begin with Q, which represents 99 mph. Then they proceed with R (106 mph), S (112 mph), T (118 mph), H (131 mph), and V (149 mph).

After V come VR (131 mph), W (168 mph), Y (186 mph), and ZR (149 mph).

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