How to Read Tire Size?

Have you ever noticed letters and numbers on your tire sidewall?  These are known as tire codes.  By gaining knowledge of these codes and what they refer to, you can get to know about the size, type, and performance of your vehicles tire. This information will allow you to enhance the riding performance of your vehicle to the fullest.  

Meaning of Tire Codes

Before starting, we will take an example of a Tire Code and break it into different parts explaining how every part conveys a unique meaning. 

Tire Type: The first letter of the tire code tells the type of tire .  There are three different types of tires.

Letter "P" refers to a passenger vehicle tire.  Cars, SUVs, crossovers, minivans, and smaller pickup trucks all come under P-Set tires.

LT stands for "Light truck tire", these are designed for heavy loads carrying vehicles like towing trailers. 

ST is referred to as a "Special Trailer". These tires are never installed on the actual vehicle that is being driven. It's only intended for use on trailer axles, as well as boat and utility trailers.

If there’s no letter at the start of the code, it means you have a metric tire which is referred to as European size. 

Tire Width: After the letter, you can see three digits, this is the width of tires in millimeters. It is also known as section width.

Aspect Ratio: The Two-Digit Number after the slash is referred to as the Aspect ratio. This is the ratio of the height of the cross-section to its width. For example, in a size P 205/65 R15 tire, the 65 means that the height is equal to 65% of the tire's width. A bigger Aspect ratio means a bigger sidewall.

Construction Type: The single letter after aspect ratio tells about the internal structure of tires. 

The letter "R" is referred to as Radial, which means the layers run radially across the tire. Most of today's tires use this as an internal structure because it provides less resistance and better road grip, comfortable ride, and more durability than previous tires.

If you see the letter "D" in tire size, this means diagonal (crisscrossed) plies, called bias-constructed tires. Some bike tires use this structure.

Wheel Diameter: The size of a wheel is measured from one end to another end in inches and this is referred to as wheel diameter and is located after the construction type.

Load Index: Next is the load index, which tells us about the maximum load capacity handled by properly inflated tires. This may be a two or three digits number.

Speed Rating: The last letter of the code symbolizes speed rating which indicates the maximum speed (safe for driving) achieved by the tires. Tires with a High-speed rating provide better control on high speed and they also handle heat better than lower-speed rating tires.