by GraMarie Walker

Created on: March 24, 2007   Last Updated: September 15, 2011

Do you realize that just about everything you need to know about your tire is recorded in the numbers located on the sidewalls? I didn't! Oh, I knew the tire size information, but not what it actually meant. The rest of that stuff was just gibberish as far as I was concerned and only meaningful for "tire guys". This just goes to show how wrong a gal can be! All of us responsible for the maintenance of a car and the replacement of our tires should know what this information signifies. Those little numbers contain specific information about the tire, its width, height and even how it is constructed, its relative tread wear potential and speed rating. When I need to know how much air my tire needs to operate properly, that's there too. It can also let us know when a bargain tire is no bargain!

Let's start with the most obvious lettering on a tire, which is almost always the manufacturer and model. This tells us the name of the company that made it and their marketing name for that specific tire like "Grabber", "Enforcer" or other catchy moniker.

Smaller, but still prominently displayed is the tire type and size designation. A common passenger car tire might read: P215/75 R 14, with 92V off to the side.

-"P" stands for passenger, LT would be for a light performance truck and HP or H/P if shown would indicate high performance tires made for special uses. Tires without the letter designation are considered "Euro Metric" and may have slightly different load capacities and inflation rates. When all else is the same, these two types may be interchangeable when used in axle pairs or full sets. Matching tires is important! I highly recommend reading the link provided under "Tire Rack Online Performance Source Mixing Tires" for information on mixing and matching tires safely.

-215 is the tire width from sidewall to sidewall. This is measured in millimeters and tires for a passenger car can range from 195 mm to 345 mm for some of the specialty tires.

-75 indicates the "Aspect Ratio" or more simply, the height of the tire from the bead or edge of rim hole to the edge of the tread. I am not going to get into the math of the aspect ratio, but a rule of thumb is the smaller the aspect ratio, the wider the tire in relation to its height. Those short, wide little tires seen on fast little sport cars are a good example of this. They are made for cornering at high speeds and keeping a lot of tread on the pavement. Depending on the intended use, the aspect ration can vary from 30

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