GMC Trucks

Plus Sizing Your Tires

Tire Topics - Plus Sizing Your Tires

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Plus sizing your wheels and tires is the best way to improve both the performance and appearance of your vehicle. By using a larger diameter wheel with a lower profile tire it's possible to properly maintain the overall diameter of the tire, keeping odometer and speedometer changes negligible. By using a tire with a shorter sidewall, you gain quickness in steering response and better lateral stability. The visual appeal is obvious, most wheels look better than the sidewall of the tire, so the more wheel and less sidewall there is, the better it looks. Please contact our sales team for assistance in the proper sizing for your vehicle.

Plus Sizing Your Tires
Reading Your Sidewall

There is a lot to learn from the sidewall of your tire. Although at first glance you may think you stumbled across tire hieroglyphics, you've actually found molded into the tires side its own user manual.

Example: P205/55R16 91W

P - identifies your tire as a Passenger Tire. The P stands for PMetric. If your tire size starts with LT rather than a P than it identifies the tire as a light truck tire.

205 - identifies the tire section width, which is the measurement of the tire from sidewall to sidewall in millimeters. This measurement varies depending on the width of rim to which it is fitted. That is why when you are looking at the tire specifications, the manufacturer will list a measuring rim width. Generally, section width will vary by 0.2 inches (5mm) per inch of rim width. For example, a 205mm tire with a section width of 8.1 inches (205mm) on a 6.5-inch wide rim will measure 8.3 inches (210mm) of section width when installed on a 7.5-inch wide rim. (There are 25.4 millimeters per 1 inch.)

Reading Your Sidewall

55 - is the two-figure aspect ratio. This percentage compares the tire's section height with the tire's section width. This aspect ratio of 55 means that the tire's section height is 55% of the tire's section width. For example, this tire has section width of 8.1 inches (205mm), which calculates to a section height of 4.5 inches (113mm).

R - indicates the construction used within the tires casing. R stands for radial construction. B means belted bias and D stands for diagonal bias construction.

16 - The last dimension listed in the size is the diameter of the wheel rim, which is almost always measured in inches.

91 - The load index and speed rating, or service description, are the numbers that follow the tire size. The load index tells you how much weight the tire can support when properly inflated. Load indices range from 75 - 105 for passenger tires, with each numeric value corresponding to a certain carrying capacity. The carrying capacity for each value can be found on a load index chart. On each U.S. passenger car tire, the load limit is listed in pounds. European tires have the load limit listed in kilograms and sometimes pounds.

W - Speed ratings are represented by letters ranging from A to Z. Each letter coincides to the maximum speed a tire can sustain under its recommended load capacity. For instance, W is equivalent to a maximum speed of 270 kph. Even though a tire can perform at this speed, Davis Pontiac does not advocate exceeding legal speed limits.

DOT Serial Number - The "DOT" symbol certifies the tire manufacturer's compliance with the U.S. Department of Transportation tire safety standards. Tires made in the United States have the DOT serial number located on the inside sidewall near the rim. Starting with the year 2000, four numbers are used for the Date of Manufacture, first two numbers identify the week and the last two numbers identify the year of manufacture.

Reading Your Sidewall

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