How to Calculate Tire Dimensions

When your tires are beginning to have a worn look, you should start thinking about replacing them as soon as you can. The last thing you want is having a flat tire in the traffic. Learn how you can know what they are talking about at the tire store when you are buying your next set.

• Prior to going to get the tires replaced, write down the numbers on your current tires. You can use these to get new ones without being overwhelmed by a fast talking tire salesman. These can be found on the tire sidewall in small print.


• Take the first number in the series. (We will use a 225/45R17 here.) The 225 stands for the width of the tire measured in millimeters from sidewall to sidewall. (For general info, dividing that number – 225 by 25.4 – will give you the inches.)


• Looking at the next two numbers–45–is the tires aspect ratio or profile. It is basically the ratio of the width to the height of the sidewall stated in percentages. This is used for determining what the tires are normally used for. High performance tires will have a much lower ratio so they can corner better.


• Observing the last number-17–is the wheel diameter in inches. If you need to covert to millimeters just use the 25.4 (from above) and multiply times 17. (431.8 in this example.)


• The letter R simply stands for radial. Basically these tires are on most automobiles and trucks today.


• Take this to the tire store and you may know as much as the person selling you the tires. At least you can hold your own in the conversation. It is not complicated once the proper information is in your hands.