![]() ![]() This means the sidewall height is 70% (.70 in calculation) of the width of the tire. The conversion is 1"= 25.4mm so for our example: 285/25.4= 11.22" width.ī- This part is the "aspect ratio" of the tire and is a relation of the tire's width to the sidewall height of the tire. To help you understand tire sizes a little better here's a quick lesson.įor an example we'll use a fairly common tire size for trucks with a 3" lift, a 285/70/R17.Ī- This is the width of the tire in millimeters. So, anyone that doesn't understand what the numbers mean, Read up so you can understand too! I also teach how to calculate the sizes to standard US measurements for times when you don't have a size calculator available, like the one on our site. I decided that far too many don't know this valuable information and set out to do a write up thats easy to understand as to what the numbers mean. You can use a conversion calculator to find the equivalent P-metric and flotation tire sizes.I was recently PMed by a member for information regarding fitment of tires on his truck, but it was obvious to me that they had very little knowledge as to what the metric sizing numbers really meant. Parts of a flotation tire size 28.5x9R17LT 115R Part of Tire Size here’s what the parts of a flotation tire size 28.5x9R17LT 115R mean. For instance, you might see a tire size in the format 28.5x9R17LT 115R.įlotation tire sizes are a little different in that they are measured in inches rather than millimeters and the numbers refer to different attributes of the tire. While euro metric and P-metric sizing are the most common, you might also see sizing using a different standard when looking for high-flotation or light truck tires. The tire size chart below shows common metric tire sizes and their height and width converted to inches.Ĭhart showing the tread width and tire height in inches for common metric tire sizes Tire Size Of course, you can use a calculator to compare two tires, but keep reading to learn how to calculate the size of a tire. Ensure the tires have a rating equal to or greater than the vehicle’s speed capability. ![]() The final letter in the tire designation is the speed rating and corresponds to the rating for the maximum speed the vehicle can travel when using the tires. ![]() The load index is a code that corresponds to a load rating for the tire. For instance, a P225/65R17 98H tire fits a wheel diameter of 17″.Īfter the rim diameter, there will be a space then another number, which denotes the tire’s load index. The next number denotes the rim diameter, or wheel size, in inches. An “R” is the most common and denotes a radial construction, but some other types might be used, such as “D” for diagonal bias construction. The letter following the aspect ratio indicates the tire construction. Similar to the aspect ratio for a TV, the aspect ratio is the ratio of the tire height to the width and is used to determine the height using a formula. The two or three numbers immediately after the slash (“/”) indicate the aspect ratio of the tire. The section width and the wheel offset need to be taken into consideration to determine where the wheel will sit in relation to the vehicle to determine if the tires will rub the wheel-well or stick out too far from the vehicle. This is the width from sidewall to sidewall and is also called the section width or tread width. The first three numbers in the tire designation before the slash (“/”) denote the tire width in millimeters. ![]() A “P” indicates that the size is a P-metric size, but there are also euro metric and LT-metric types. The first letter in the tire designation is the vehicle type and denotes which type of designation the tire uses. A P-metric size designation contains several key pieces of information about the tire. Today, most passenger vehicles use metric or P-metric tire size designations such as P225/65R17 98H. This is the tire size and pressures suggested by the manufacturer for the vehicle, but as stated above, it might not match the tires that are currently installed. Note that while this is the actual tire installed on the vehicle, it might have been replaced in the past and it’s not guaranteed to be the suggested size for the vehicle.Ģ: A yellow or white “tire and loading information” sticker should be visible on the inside of the driver’s side door frame. You can find it it two places.ġ: Each tire will have the size code printed or embossed in the sidewall of the tire. But, tire sizes can be confusing, and it might not be immediately clear what the numbers in a tire size mean, or even where to find it.Īt this point you might be wondering where to find the tire size for your vehicle. If you need new tires, the first thing you need to know is how to size them for your vehicle. Remember that the circumference is 80.8″. For example, let’s find the revolutions per mile of the 245/40R18 tire. ![]()
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