Tire Sidewall & Tire Size

How to Read the Side of Your Tire

ASPECT RATIO
The relationship of a tire's sidewall height to its section width.

DOT MARKINGS
A code (tire identification numbers) molded into the sidewall of a tire signifying that the tire complies with U.S. Department of Transportation (DOT) motor vehicle safety standards. The DOT is followed by ten, eleven or twelve letters and/or numbers that identify the manufacturing location, tire size and manufacturer's code, along with the week and year the tire was manufactured.

LOAD-CARRYING CAPACITY
Indicates how much weight a tire is certified to carry at maximum inflation pressure.

LOAD INDEX
An assigned number ranging from 0 to 279 that corresponds to the load-carrying capacity of a tire.

OVERALL DIAMETER
The diameter of the inflated tire, without any load.

OVERALL WIDTH
The distance between the outside of the two sidewalls, including lettering and designs.

SIZE
The combination of tire width, construction type, aspect ratio, and rim size used in differentiating tires.

SPEED RATING
This indicates the maximum safe speed at which a tire is certified to travel under specified conditions. Speed ratings range from A (the lowest) to Y (the highest).

TIRE DESIGNATION
An alphanumeric code molded into the sidewall of the tire that describes the tire's size, including width, aspect ratio, rim diameter, load index, and speed rating. Most designations use the P-Metric system.

TIRE BRAND
This is the brand or manufacturer of your tire.

TIRE PATTERN NAME
The tire pattern name is the model or name designated to a particular tire - this information is usually found after the manufacturer's name on the sidewall.

TIRE WEAR INDICATOR
Tread wear indicators ("wear bars") are located at the base of the main grooves and are equally spaced around the tire. The tread wear indicators, which look like narrow strips of smooth rubber across the tread, will appear on the tire when that point of wear is reached. When you see these wear bars, the tire is worn out and it's time to replace the tire. Always remove tires from service when they reach a remaining tread depth of two millimetres (2 mm). Another easy way to check is to do the coin test. Take a five cent coin and place it with Queen's head down in the tread groove. If the tread covers the top of the Queen's head, then your tires are OK. If the tread does not cover the top of the Queen's head, it is time to replace your tires.

TIRE TYPE
This designates the type of vehicle the tire fits. P is for passenger metric. Other letters are LT (for light truck), T (for temporary spare) and ST (for special trailers). If your tire has no letter, it signifies that your tire is a euro "metric" size.

TIRE WIDTH
The width of your tire from sidewall to sidewall. In this example the width of the tire is 225mm.

TIRE ASPECT RATIO
This identifies the tire's aspect ratio, which is the relationship of the tire's sidewall height to the tire's width. In this example, the sidewall height of the tire is 55% of its width. The lower the ratio, the smaller the sidewall height, which means better cornering, but a rougher ride.

TIRE CONSTRUCTION
This is the tire's internal construction, which is "radial." Almost every tire on the road has radial construction, which means the cords of the carcass plies inside the tire "radiate" directly across from one side of the tire to the other. Other letters used are D, for diagonal construction, and B, for belted.

WHEEL DIAMETER
This number (in inches) indicates that the tire is designed to fit on a wheel with a 18-inch diameter.

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