by Theresa England

Created on: February 10, 2010   Last Updated: February 12, 2010

There is such a misconception as to what all the numbers on your tires mean. The reason the tire manufacture has these numbers branded into your tire is to tell them a number of things. We will begin with the most basic, the letters that are branded into the tire. If the series of size numbers begin with a P, this simply means that this tire is for a passenger car. If it begins with a LT it means light truck and T would mean temporary - as in your spare.

Let's now take a look at the numbers that follow the letters. E.g.: 235/75/16.These numbers represent the size of your tires.The first number is your width. This is measured in millimeters, therefore 235millimeters is your tire width. The second number in the series is 75.this is the aspect ratio of the tire i.e.: this tells you the height of the tire from the road to the tread. The smaller the aspect ratio is the wider the tire would be to the height; as in racing tires, these are also known as low profile tires. The height or aspect ratio is much lower because of the needed traction for the road. Now the last of the series of numbers is 16. This represents the rim size. So to simplify things...your tire size is P235/65/17; this tire is for a passenger car, with a tire width of 235millimeters, it has an aspect ratio of 65 and the rim size is 17.

The other branded numbers and letters found on the tire are for rating purposes.We will start with the number following the size of the tire. This is normally a two digit number followed by a letter .E.g. :235/65/17 89S.This represents the load index and the speed rating. The higher the tires load index number the higher the load capacity is.There are charts to follow to get into the technical side of the load capacity. The standard for a load capacity of 89 is 1279lb.So if necessary the tire chart would be able to give you this information. The letter following the numbers is the speed ratings. The letter S represents family sedans and vans, this gives a speed -rating of no more than 112mph; the higher speed rated tires are for sports cars.  The letter Z is one of the highest speed rated tires. This is capable of speeds over 149 mph.

There are other markings on the tire that tells the car manufacture what the traction, temperature and tread wear is.  These are usually a series of letters. Tire traction is rated AA;A;B:or C.  This measures the tires  ability for the tire to stop on wet roads, the higher the rating the better the traction. The temperature also rated with the letters A:B:C. This measures how quickly the tire dissipates the heat.

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