Every passenger tire sold in the US has a string like “400 AA A” molded into its sidewall. It’s not a size code or a date stamp — it’s the Uniform Tire Quality Grading (UTQG) rating, a federally mandated label that’s been required since 1979. It’s also one of the most misunderstood numbers in car ownership, because the two most common assumptions about it — “bigger treadwear number means it’ll last longer, full stop” and “the government tested this tire” — are both only half right.
The three grades, and what each one actually measures
Treadwear is a comparative index. A tire graded 400 is rated to wear roughly twice as long, under the test’s specific conditions, as one graded 200 — but there is no direct “400 = 40,000 miles” conversion. It’s a relative number, not an odometer prediction.
Traction grades wet-pavement stopping ability on a scale of AA, A, B, C (AA is best), measured by locked-wheel braking distance on specified asphalt and concrete government test surfaces. It says nothing about dry grip, snow, or cornering — just straight-line wet stopping.
Temperature grades a tire’s resistance to heat buildup at sustained high speed, from A (best) to C. Every tire legally sold in the US must at least meet grade C; A and B ratings indicate a wider safety margin at speed.
The catch: manufacturers assign their own grades
This is the part most “best tires” content glosses over. NHTSA does not run these tests. Under the UTQG regulation (49 CFR 575.104), the tire manufacturer tests its own product against its own reference tire and self-reports the grades. NHTSA’s role is to spot-check compliance and investigate discrepancies — not to independently grade every line in the market.
The practical effect: treadwear numbers are genuinely useful for comparing tires within one brand’s own lineup — a Michelin graded 820 really is rated to outlast a Michelin graded 500. Comparing across brands is much rougher, because each manufacturer picks its own reference tire and testing conditions. A 600-treadwear Goodyear and a 600-treadwear Continental are not guaranteed to wear at the same real-world rate. Treat cross-brand UTQG comparisons as a rough sort, not a lab-verified ranking — and treat any “best tires by UTQG” list (including ours) as ranking manufacturer claims, not independent test results.
Why the mileage warranty is the number that keeps UTQG honest
Because treadwear grades are self-reported, the number that actually costs the manufacturer money if they’re wrong is the mileage warranty — a contractual promise, backed by a pro-rated replacement, that’s a much stronger incentive to be accurate than a sidewall grade nobody enforces retail-side. A tire graded 820 treadwear with an 80,000-mile warranty (like Michelin’s Defender T+H) is a manufacturer putting its money behind the number. A high treadwear grade with no comparable warranty is a weaker signal. We treat the two together — grade plus warranty — as the real evidence, which is why both are sortable columns in our UTQG tire data table.
Winter tires don’t get a UTQG treadwear grade
Tires branded specifically as winter/snow tires are exempt from UTQG treadwear and temperature grading entirely — their tread compounds are designed to stay pliable in the cold, which would grade poorly against the UTQG test’s warm-weather wear and heat-resistance conditions even though that’s exactly the behavior you want in snow. If a “tire” in a treadwear comparison shows no grade at all, that’s very likely why. It’s a separate reason all-weather tires (3PMSF-rated, but not dedicated winter tires — like Michelin’s CrossClimate2 or Goodyear’s Assurance WeatherReady) still carry full UTQG grades: they’re all-season tires with a snow-traction certification layered on top, not winter-tire-exempt.
What we did with this
We pulled UTQG grades for a curated set of current, widely sold passenger all-season and touring lines from the major brands, cross-referenced with each line’s manufacturer mileage warranty, into a sortable data table. Our Top 10 Long-Wearing All-Season Tires list is built directly on that table — ranked on treadwear grade, mileage warranty, and traction together, with a pick for several real use cases (best overall, best warranty, best budget, best for SUVs, best UHP all-season). Every number carries the same caveat as this article: it’s the manufacturer’s own claim, not an independent lab result — read it as a starting point for cross-shopping, and confirm the exact grade on the size you’re buying before you check out.