Ever Wondered What Do Those Numbers On Side Of Tires Mean? Mystery Solved

Tire numbers

Ever looked at your car’s tyre and wondered what those alphanumeric codes mean? They are not just for the US Department of Transportation or the manufacturer to understand, you too can extract valuable information from them. Apart from brand, model and size there is more information than you think.



First letter usually indicates the tire class. As LT means Light Truck and designates that the tyre is suitable for small payload trucks. Same way tyres for passenger cars are allotted the letter “P”

 Section Width Tread(mm)


Next three digits account for the section width of the tyre. Section width is basically the width of the tyre from one side wall to the other.

Aspect Ratio


This actually tells you about the height of the side wall. An aspect ratio for example of 45 means that the side wall height is 45% of the section width.



This letter donates the construction. If it is R it means radian which means layers of fabric run radially across the tyre.

Wheel Diameter


This number is designated for the wheel diameter, which is usually given in inches.

Speed Rating

This states the maximum speed at which a properly fixed and inflated tyre can run on. For example, a rating of H  indicates the maximum rating of 210Km/h. Usually this matches the maximum speed of your car. Z donates the highest rating, and Z rating tyres also have an extra W or Y rating after the load index telling the actual speed.

Load Index

Load Index indicates the maximum load the tyre can carry. It is advised you install tyres with greater or equal load index as stated by your car’s manufacturer.

 US Department of Transportation Markings


All tyres must have a DOT number which indicates that they have either met or passed the DoT minimum criteria. The code in the picture represents the plant it was manufacturer in which is given by R8, the size as told by LN, LMJR conveys the user about additional information on construction and the final digits represent when this tyre was made, in the picture this tyre was made in week 46 and 10th year of the decade.

Uniform Tire Quality Grading (UTQG) Marking

DoT requires each manufacturer to grade its tyre safety rating through UTGQ. Three properties are to graded treadwear, traction and temperature resistance. Tread wear might refer to durability and not necessarily the life of the tyre. The traction ability is actually the tyres ability to stop in a straight line on wet concrete and not its cornering ability. The traction grades consist of AA, A, B or C, with AA being the highest. Heat grade refers to the rate at which tyres temperature increases at high speed, grades are given A to C with A being the best as these tyres dissipate heat quickly.

Maximum Inflation Pressure and Load

Maximum inflation pressure indicates the maximum air pressure tyre can hold during operation.

So based on all these factors, you need to decide the tire specs that work for you. Hope this was useful. Stay tuned to Wonderful Engineering!

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