Tire Traction Grades AA, A, B and C Explained
What the traction grade measures
The traction grade shows a tire’s ability to stop on wet pavement, measured under controlled conditions on government test surfaces of asphalt and concrete. The grades, from highest to lowest, are AA, A, B and C. That’s how the federal rule, 49 CFR 575.104, puts it.
AA is a single grade, the top one. It isn’t two A’s.
How the test works
The rule describes the test: a test trailer is towed at 40 mph over wetted asphalt and concrete skid pads at Goodfellow Air Force Base in Texas. One wheel is locked and the friction (“traction coefficient”) is recorded. The result is adjusted against a standard reference tire tested in the same session.
A grade requires minimum results on both surfaces. Using the rule’s thresholds for the adjusted coefficient:
| Grade | Asphalt | Concrete |
|---|---|---|
| AA | more than 0.54 | more than 0.38 |
| A | more than 0.47 | more than 0.35 |
| B | more than 0.38 | more than 0.26 |
| C | 0.38 or less, or concrete 0.26 or less |
These are coefficients, not stopping distances. The rule gives no conversion to feet or seconds, and neither do we.
What the grade leaves out
The rule carries a warning that has to be included with the grade: the traction grade “is based on straight-ahead braking traction tests, and does not include acceleration, cornering, hydroplaning, or peak traction characteristics.”
The grade also says nothing about snow or ice. And the rule says a tire marked C “may have poor traction performance.”
Traction vs. temperature letters
Both grades use letters, which makes them easy to mix up. Traction uses AA, A, B and C and is about wet braking. Temperature uses A, B and C and is about heat in a lab test. On a sidewall the letters always follow their label, so read “TRACTION” and “TEMPERATURE” before the letter.
Finding AA-traction tires on this site
You can set “Traction: AA” in the filter tool on our home page, or see the ranking of top grades: AA traction and A temperature.
Source
49 CFR 575.104, paragraphs (d)(2)(ii) and (f), and Figure 2. Grades on this site: NHTSA UTQG ratings data (data source).