Tire Temperature Grades A, B and C Explained

What the temperature grade describes

The temperature grades are A (the highest), B and C. They represent the tire’s resistance to generating heat and its ability to dissipate heat, tested under controlled conditions on an indoor laboratory test wheel. This is the wording of the federal rule, 49 CFR 575.104.

The letter is about the tire’s performance on that test. It is not an outdoor temperature range or a climate rating.

How the lab test works

Per the rule, the tire is mounted, inflated to a set pressure and kept at 95 °F. It is pressed against a large steel test wheel at 88 percent of its maximum rated load. After a two-hour warm-up stage, the wheel speed is raised in 25 rpm steps, each lasting 30 minutes, up to 575 rpm or until the tire fails.

A stage counts as completed only if the tire shows no visible separation, chunking, broken cords, cracking or open splices, and has kept its pressure.

What C means

The rule says grade C corresponds to the level of performance all passenger car tires must meet under Federal Motor Vehicle Safety Standard No. 109. Grades B and A represent higher levels of performance on the lab test wheel than that legal minimum.

Why heat matters, and the built-in warning

The rule explains why heat is graded at all: sustained high temperature can cause tire material to degenerate and reduce tire life, and excessive temperature can lead to sudden tire failure.

It also requires a warning with the grade: the temperature grade “is established for a tire that is properly inflated and not overloaded. Excessive speed, underinflation, or excessive loading, either separately or in combination, can cause heat buildup and possible tire failure.”

A higher grade doesn’t make up for wrong pressure or overloading. For the right pressure and load for your vehicle, follow the vehicle maker’s information.

Temperature grades in the data

Most rated lines in NHTSA’s data carry an A or B temperature grade. You can browse the lines published with a B temperature grade, or filter by grade with the finder.

Source

49 CFR 575.104, paragraphs (d)(2)(iii) and (g), and Figure 2. Grades on this site: NHTSA UTQG ratings data (data source).