What do the numbers in a tire size mean

Together these figures make up the tires service description. 1 These are some of the most important numbers on any tire as they tell you how big your tires are.

Inch marking such as 28 x 1 58 x 1 38 approximate outer diameter x tire height x tire width is also common.

What do the numbers in a tire size mean. Is the ratio of the height of the tires cross-section to its width. The two-digit number after the slash mark in a tire size is the aspect ratio. For example in a size P21565 R15 tire the 65 means that the height is equal to 65 of the tires width.

The bigger the aspect ratio the bigger the tires sidewall will be. Tire size specifications are outlined by the numbers and letters found on the sidewall of tires. It is important that we understand tire geometry and be informed of the parameters that govern their performance.

Tire sizes are defined by specifications such as the type width aspect ratio speed rating tire construction type and service description. C Commercial Example. 31x1050R15 C 109R Euro-Metric tire sizes ending with a C are commercial tires for use on delivery trucks and vans capable of carrying heavy loads.

In addition to the C designation these sizes are also branded with a load range and service description rating load range B C or D. P Passenger Car Tire The first letter on a tire indicates the tires class. P designates this tire as a passenger car tire an LT before the tire size would mean the tire is a light truck tire and a European metric tire would have no letter before the tire size.

245 Section WidthTread mm. Understanding Three Numbers in Tire Sizes. The first number in a tires size say 225.

The final number group the 18 is the size of wheel the tire fits. In our example size the tire will fit a 18-inch wheel. Some manufacturers build off-road tires using inches instead of millimeters so you may see sizes like 3317 This simply means the total height of the tire is 33 inches and it fits a 17-inch wheel.

If theres no letter before the first number you have a metric tire most commonly referred to as European size. Its also measured in millimeters but may have different load capacity than a P or LT tire. TIRE WIDTH The three-digit number following the letter is the tires width from side to side looking at the tire head on in millimeters.

Also called the section width this measurement is taken from outer sidewall to inner sidewall. The following tire numbers represent rimwheel diameter measured from one side to another. The two-digit number is in inches and the most regular sizes are the following.

8 10 12 13 14 15 17 18 19 20 22 23 24 26 28. You can see such tires on most passenger vehicles. 1 These are some of the most important numbers on any tire as they tell you how big your tires are.

In this case the tire is 245 millimeters at its widest point when its mounted on a wheel of. The first number is your overall diameter of the tire. In this example the tire diameter or height is 33 inches tall.

The second number represents the width of the tire. In most cases with inch measurement tires the width will have a50 decimal after the initial number. If a tire size has three sets of numbers 15x600-6 26x1200-12 31x1550-15 then the first number 26 x1200-12 is the approximate height in inches the second number 26x 1200 -12 is the approximate width in inches and the third number 26x1200- 12 is the rim diameter in inches.

An example of tractor tire sizes expressed in the standard format would be 149-42. The 149 means the tire is 149 inches wide and the 42 tells us that this tire fits a 42-inch diameter wheel. The dash - indicates the tire construction is bias-ply but this could be an R if the tire is radial.

If your tire size starts with LT rather than a P then it identifies the tire as a Light Truck tire. 225 identifies the tire section width which is the measurement of the tire from sidewall to sidewall in millimeters. This measurement varies depending on the rim to which it is fitted.

There are 254 millimeters per 1 inch. After the forward slash the next number on our example tire is 65. This is the tires aspect ratio or its percentage of width to sidewall height.

In this case 65 means that the tires height is. A smaller number means a lower profile and the height-to-width ratio is shown as a percent. For example if the aspect ratio is 90 that means that your tires cross-sectional height is 90 of its width.

If the tire has the metric alpha or low-profile inch numbering system the aspect ratio will appear immediately after the width. 28 x 140 states the approximate outer diameter 28 inches and the tire width 140 inches. Inch marking such as 28 x 1 58 x 1 38 approximate outer diameter x tire height x tire width is also common.

Inch sizes are not precise and lack accuracy. The first number is 18 which means the tire is roughly 18 in diameter. The next number is 850 which means the tire is roughly 85 inches wide and the final number is 8 which means the tire mounts on a wheel with an 8 diameter.

Both speed rating and load index are part of a group of three digits at the tail end of the tire size information. Together these figures make up the tires service description. If your vehicle is still equipped with its factory tires you can refer to the drivers side doorjamb placard which includes tire information.