Coupled with the “max load” number, which is found near to “max press” on the sidewall, you can know the maximum load-carrying ability of a tire. Know this: It’s air pressure that allows the tire to carry a load. At one pound per square inch (psi) of air pressure a tire can support no weight. To increase its load-carrying capacity, air pressure must be increased. (Imagine a plastic soft-drink bottle: With the top off, it’s easily crushed, but new and unopened it can support a grown man.) However, at some pressure, adding more air to the tire will not provide increased weight-carrying capacity: That’s what the “max load/max pressure” means.
Molded into every tire sidewall is a series of codes that give valuable information to the consumer regarding that
specific tire, such as name of the tire, its size, whether it is tubeless or its tube type, the tire grade, speed rating, the maximum load, maximum inflation, important safety warnings, etc. Let’s look at a typical passenger car tire to see what those letters and number really mean:
Example: P255/60R15 102T
“P” means this is a passenger car tire (as opposed to a tire made for a truck or other vehicle). P-metric is the U.S. version of a metric tire-sizing system. LT designates the tire as a light truck (or SUV) tire.
“255” Section Width: The width of the tire in millimeters from sidewall to sidewall. This measurement varies depending on the width of the rim to which the tire is fitted: larger on a wider rim, smaller on a narrow rim. The number on the side of tire indicates the width measured with the tire fitted to the tire manufacturers recommended rim width.
“60” Aspect Ratio: The ratio of height to width (this tire’s height is 60 percent of its width).
“R” Construction: How the plies are constructed in the tire carcass. “R” means radial. “B” in place of the “R” means the tire is belted bias construction. “D” in place of the “R” means diagonal bias construction. The vast majority of modern cars, SUVs, and trucks use radial tires.
“15” Rim Diameter: The diameter of the steel or aluminum wheel in inches the tire will fit.
“102” Load Index: This tire has an industry-standard maximum load of 1,874 lbs. Different numbers correspond to different maximum loads. The maximum load is shown in lbs. (pounds) and in kg (kilograms), and maximum pressure in PSI (pounds per square inch) and in kPa (kilopascals).
“T” Speed Rating: This tire has an industry-standard maximum service speed of 118 mph. Tires using an older European system carry the speed rating in the size description: 255/60HR15. Different letters correspond to different maximum service speeds.
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