UTQG grades: what treadwear, traction and temperature mean

Most passenger tires sold in the United States carry three grades moulded into the sidewall, in this order: a number, then one or two letters, then one letter. 600 A B is a treadwear grade of 600, a traction grade of A, and a temperature grade of B.

The three come from three unrelated tests, and only two of them have externally defined pass marks.

Treadwear: a projection, self-assigned

A convoy of vehicles runs the candidate tire alongside a Course Monitoring Tire over a fixed public road loop in West Texas for 7,200 miles, with wear measured at intervals. The candidate's wear rate is compared with the control tire's, which is defined as 100, and the ratio is rounded to a multiple of 20 and moulded on.

So 400 means the manufacturer projects four times the control tire's life; 800 means eight times.

The critical qualifications:

• The grade is assigned by the manufacturer, from its own testing, using the standardised method. It is not certified by an outside body.
• It is a projection from 7,200 miles, not an observation of a tire worn out.
• It is comparable within a brand and unreliable between brands. Manufacturers apply different internal margins, and there is no mechanism forcing two companies' 500s to mean the same thing.
• It converts to no mileage figure whatsoever. A grade does not become a warranty, and tread life on your vehicle depends on load, pressure, alignment, climate and how you drive.

Traction: a wet skid coefficient with published thresholds

This one has hard numbers behind it. The tire is dragged, locked, across two wet test surfaces — one asphalt, one concrete — and the resulting coefficient of friction is measured. The grades are defined by thresholds on both surfaces at once:

Grade	Wet asphalt	Wet concrete
AA	above 0.54	above 0.38
A	above 0.47	above 0.35
B	above 0.38	above 0.26
C	0.38 or below	0.26 or below

Two things this does not measure, and the omissions are large: it is straight-line and locked, so it says nothing about cornering grip, and it is wet only, so it says nothing about dry braking, snow or ice. A tire's snow capability is a separate question with a separate marking — M+S and the three-peak snowflake cover it.

Temperature: heat resistance at speed

The tire is run on an indoor test wheel at increasing speeds, and the grade records the highest band it completed without failing:

• A — sustained speeds above 115 mph.
• B — between 100 and 115 mph.
• C — between 85 and 100 mph.

Grade C is the minimum permitted for a passenger tire, so every graded tire has cleared it. The test is conducted at a specified inflation and load, which is the point of it: heat resistance collapses when a tire is run underinflated, and the grade assumes it is not.

Note the overlap with the speed symbol. They are related but not interchangeable — the speed symbol is an endurance test at a rated load, and the temperature grade is a heat-resistance band. A tire can carry a high speed symbol and a temperature grade of A, and the two were established separately.

Why the treadwear numbers cluster where they do

Scan a shelf and the grades bunch: touring tires in the 500s to 800s, all-season passenger tires in the 400s to 600s, summer performance tires in the 200s to 300s, and track-focused tires below 200.

That spread is real and it reflects a genuine engineering trade. Grip comes from a compound that deforms into the road surface and recovers, and the same property that produces grip produces wear. A compound optimised to last is one that resists deforming, which is the opposite requirement.

What the spread does not support is fine-grained comparison. A 620 and a 640 from different manufacturers are indistinguishable claims; a 620 and a 300 are telling you something real about what each compound was designed to do.

Which tires carry grades, and which do not

The grading requirement covers passenger car tires. It does not extend to:

• Light-truck tires marked LT,
• Deep tread, winter and snow tires,
• Temporary spares,
• Trailer, off-road and special-purpose tires.

That absence catches people comparing an all-terrain LT tire with a highway P-metric tire: the grades exist on one and not the other, and no grade is not a low grade.

How to use the grades honestly

• Within one manufacturer's range, treadwear is a genuine ranking of that company's own compounds against each other.
• Traction grades are comparable across brands, because the thresholds are absolute and published.
• Temperature grades rarely discriminate, because most modern tires reach A.
• Nothing in the set describes ride, noise, dry grip, wet cornering or snow.

The grades sit alongside the size code, the service description and the identification number as one of four independent markings, none of them derived from the others. Neither the grades nor this site's arithmetic says anything about whether a tire suits your vehicle — the geometry is computed here, the grades are moulded there, and the fitment decision belongs to neither.