Whether you need information on tire pressure or wheel diameter, a tire's sidewall carries a lot of useful information when shopping for new car tires. Each sidewall is stamped with tire codes, which are a series of alphanumeric digits that lists various specifications. However, the combination of different numbers and letters can be tough to translate. Here is a helpful break down for reading tire codes.
Reading tire sizes
Tire size specifications start with one or two letters that specify the tire class. In most cases, this is either indicated by a P for a passenger vehicle or LT for SUVs or light trucks. The tire type is followed by tire width, which is a three-digit number measuring tire width from sidewall to sidewall in millimeters.
The tire's aspect ratio is listed after a slash to separate it from the tire class and width.This two-digit number is a percentage comparing sidewall height to the tire's width. After aspect ratio, you'll typically notice a letter R. This notes the internal construction of your tire, and most tires are constructed with a radial configuration. Other construction codes that might also appear includea D to denote diagonal construction or a B for belted construction.
Tire size codes conclude with a two-digit number listing the wheel diameter in inches. The wheel diameter indicates which size wheel the tire is fitted. This is important for drivers looking to upgrade their rims. If your new wheels are bigger, then you'll need to find a set of tires with larger wheel diameters.
Learn more about tire sizes
Tire load and speed rating
Load index and speed rating are listed to the right of tire size codes. The tire load index determines the maximum weight a properly inflated tire can safely support. The larger the number, the higher capacity your tires can handle. A tire load index chart translates the two or three-digit figure to the exact load capacity in pounds.
Tire load index is followed by a letter that marks the speed rating.Tire speed rating specifies a tire's maximum sustainable speed. This is scored using a letter, which can be converted into exact speeds using a tire speed rating chart. Higher ratings usually mean a tire can handle better at legal street speeds.
Tire DOT code
The U.S. Department of Transportation tire code is a serial number recorded in case of a recall. This figure is found along sidewall edge near the rim starting with "DOT." A tire DOT code lists the manufacturer's code and a tire manufacture date. The tire date code marks a tire's production year and is placed at the end of the DOT code.The date lists the week the tire was mass-produced and is followed by a one or two digit number representing the year it was made.
Learn more on how to read tire date codes
Uniform Tire Quality Grading ratings are featured on the bottom of sidewall and list a tire's treadwear traction and tire temperature grades. These ratings are established from tests administered by the manufacturer that are required by the National Highway Traffic Safety Administration. A treadwear rating measures a tire's durability in comparison to a standard reference tire. The higher this three-digit is, the longer the tread and actual tire should last.
Tire traction rating measures how a tire stops on wet roads. These results are based on performances in controlled tests and are graded as AA, A, B or C. Traction ratings with a AA grade means a tire has the best possible traction while a C grade denotes the lowest. The temperature ratinguses a similar system to score a tire's ability to handle heat at high speeds. These are rated from A through C, with A being able to withstand the most heat.