![]() Just as your load index number corresponds to a particular load, your speed rating letter corresponds to a specific speed capability based on a standardized laboratory test.įor example, a tire with a speed rating "S" is rated for up to 112 mph, while a tire rated "R" is up to 106 mph. The final figure in a tire size sequence is the speed rating indicated by a letter: P225/70R16 91S. If there is no load index measurement on your tires, check the owner's manual or contact your local Bridgestone tire dealer for more information. This is because the load index is not required by law to be printed on tires. Beginning with one and ending with 150, numbers in the load index represent carrying capacities of 99 to 7385 lbs.Īdditionally, you may not find this number present on all tires. Instead, the number corresponds to a specific load capacity listed in an index. It is called the load "index" because the figure doesn't tell us the precise number of pounds the tire can support, at least not by itself. The load index tells us how much weight, in pounds, the tire can support when fully inflated: P225/70R16 91S. The next figure needed to read tire size numbers is your tire's load index. Tires designed to fit a 16-inch wheel diameter will not stretch to fit on new 18-inch rims. Take note: if you decide to change your rims' size, you will also need to get new tires that are compatible with the change in size. For example, a tire with the P225/70R16 91S would fit a rim with a 16-inch diameter. Radial construction means the tire's internal ply cords are oriented in a radial direction (at 90 degrees to the centerline of the tread). In fact, you will almost always see the letter "R" on tires as radial tires have been the industry standard for over 40 years. But radial tires represent the vast majority of tires on the road in the United States today. "Bias-ply" tires were used on automobiles and light trucks until the '70s," reports the classic car site, Hemmings. There are two types of construction that you may see on the sidewall of a tire "R" refers to the internal structure of your tire and gives you a general idea of its stability. CONSTRUCTIONĪfter the aspect ratio comes a letter to indicate the tire's construction: P225/70R16 91S. Lower aspect ratio tires, such as a 60 series, generally offer vehicle handling performance advantages over higher aspect ratio tires, such as a 75 series. If a tire has an aspect ratio of 70, it means the tire's height is 70% of its width. Tire makers calculate the aspect ratio by dividing a tire's sidewall height by its width. Aspect ratios are delivered in percentages. ASPECT RATIOĪfter the slash mark, the next number you see is for the tire's aspect ratio, which essentially tells you how tall your tire's profile is: P225/70R16 91S. Thus, a tire with the measurement "P225" is for a passenger vehicle and has a nominal width of 225 millimeters. Tire width always refers to the measurement from one sidewall to another. The first number to appear in your tire size information is the width, in millimeters, of the correct tires for your vehicle: P225/70R16 91S. Light truck tires are designed to be used on vehicles capable of carrying heavy cargo or pulling trailers. If you see "LT" instead of "P," it's because you need "light truck" tires – "LT" is short for "LT-metric," which is a designation by the Tire and Rim Association for a "light truck" type tire. A "P" signifies the tire was designed to primarily be used on passenger vehicles, which can include cars, minivans, SUV's and other light-duty pickup trucks. The "P" is short for "P-metric," which is a designation by the Tire and Rim Association for a "passenger car" tire type. THE LETTERS "P" AND "LT"įor most vehicles, you'll see the letter "P" before the number sequence begins: P225/70R16 91S. We'll be using this tire size as an example: P225/70R16 91S. Let's take a look at what each number or letter stands for, one by one, in the order they appear in your tire size data. Let's break down how to read car tire size. Don't worry if it looks confusing at first - every letter and number has a straightforward meaning. However, no matter where you find your tire size, you will have to decipher a sequence of numbers and letters. You can also find tire size data on the sidewall of your current tires (assuming they're the proper size). The best place to start looking is the owner's manual.ĭon't worry if you can't locate the manual you may also find a tire fit guide in these locations: No matter what vehicle you drive, finding the manufacturer-recommended tire size should be easy. Knowing how to read car tire sizes also means understanding terms like load index and speed rating that affect your vehicle's overall capabilities. While actual, physical measurements like width and diameter are factors in finding the right tire size, there are additional details to consider.
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