Sports Utility Vehicles and lifted trucks have made off-roading a common venture in the United States. Even drivers with regular full size trucks can purchase "lift kits" that lift their truck to make it off-road ready. After lifting a truck, however, it is important to be careful about choosing a new tire size to go with your new lift kit. Luckily, there is a simple formula for choosing the correct tire size for your vehicle.
Look on the side of your current tires to obtain your current tire size. The tire size will be in the following format: 225/50R16 with the dimensions of your specific tire in place of the numbers provided here.
Write down the three sets of numbers. For a tire with the size information 225/50R16, you would write down 225, 50, 16. The first number is in millimeters and stands for the tire's width from sidewall to sidewall. The second number is the tire's aspect ratio or ratio or sidewall height to section width (more on this later). The third number is the diameter of your wheel, measured in inches.
Multiply the tire's width by the aspect ratio. Write the answer down. This number is the height of one sidewall of your tire. For the example, the equation would be 225 x 0.50 = 112.5.
Multiply the diameter of your wheel by 25.4 to convert the inches into millimeters. Write the answer down. For the example, the equation would be 16 x 25.4 = 406.4.
Use the equation 2 x the height of one sidewall in millimeters + the diameter of the wheel in millimeters = the diameter of the tire. For the example, the equation would be 2(112.5) + 406.4 = 631.4. This number is the overall diameter of your tire.
Select a tire that is at most 15% larger in diameter than your current tire. To find a diameter that is 15% larger, multiply your tires diameter by 1.15. For the example, the equation would be 631.4 x 1.15 = 726.1. The largest sized tire that could be installed on the vehicle in the example would have a diameter of 726.1 millimeters.
