Understanding Tire Sizes for Your Vehicle

Many people have no idea what the tire size is for their vehicle much less what those numbers mean. There is a tag on the drivers' side door that tells you the size of your tires and any other manufacturer recommended sizes. These are the only sizes that should be put on your vehicle. They are specified by the manufacturer for maximum safety and comfort. Many states also have state inspection laws that require the inspection mechanics to fail your vehicle if it has tires other than the manufacturer specified sizes on it.

Do you know what the P225/50R16 91S on your tire means? Amazingly, a lot of people do not. The "P" means it is for a passenger vehicle and is seen on cars, mini vans, SUV's, and small trucks. The "225" is the width of the widest point of its outer sidewall to the widest point of its inner sidewall when mounted. The "50" is the percent in which the sidewall height is compared to the width. So with the width being 225 millimeters the sidewall height from the rim to the tread is 112.5 millimeters. The "R" is how your tire is made or the internal construction of the tire. In this case, the R means radial. The "16" is the rim size. The "91S" are the service description for the tires. The"91" is the number that determines the load in which the tires can handle. For example, the 91 can handle 1356 pounds. The higher the number the higher the load capacity. The "S" is the speed rating of the tire. An S speed rating has been determined to be safe for up to 112 miles per hour. The further down the alphabet the higher the speeds that are considered safe for that tire.

Generally speaking, a sports car will have a wide width with a low percentage of sidewall and a low alphabet letter (usually W, Y, or Z) for maximum steering and handling capabilities. A passenger car will have a medium width with a higher percentage of sidewall for a more luxury style ride.

So now, you are wondering why you need to know this. Well the answer is simple. You need to understand what these numbers and letters mean to accurately purchase tires for your vehicle. Most mechanics will help you select the right tires for your needs, but it is helpful when you understand the differences from one tire to the next.