Traction grade (AA, A, B, C)

How to read it

The traction grade is one of the Uniform Tire Quality Grading Standards grades (49 CFR 575.104): the word TRACTION followed by AA, A, B or C. The regulation’s explanation says the grades represent the tire’s ability to stop on wet pavement, measured on government test surfaces of asphalt and concrete; the skid pads are ones NHTSA establishes and monitors. Each grade needs a minimum adjusted traction coefficient on both surfaces: A needs more than 0.47 on asphalt and 0.35 on concrete, and AA more again (0.54 and 0.38). A tire at or below 0.38 on asphalt, or 0.26 on concrete, is graded C. NHTSA’s tire page says a higher grade should let a car stop on wet roads in a shorter distance.

Also searched as: traction rating, UTQG traction.

What the grade leaves out

The regulation’s warning says the traction grade is based on straight-ahead braking traction tests, and does not include acceleration, cornering, hydroplaning or peak traction. Its explanation adds that a tire marked C may have poor traction performance. USTMA’s guide makes the same point about cornering.

How grades are spread

NHTSA’s tire page gives the spread across current tires: 15% are rated AA, 77% A and 7% B, and only four tire lines are rated C.

Tires without a grade

The grades apply to new passenger car tires. Winter-type snow tires, temporary spares, tires for rims of 12 inches or less and limited production tires are exempt (see the treadwear grade).