Tire FAQ: fitment, replacement, ratings, EV & seasonal tires

Your factory tire size is printed on the driver-door placard (the white-and-yellow sticker on the door jamb) and in your owner's manual. It reads as three numbers — for example 225/45R17 — meaning 225 mm wide, 45% sidewall aspect ratio, on a 17-inch rim. Any tire matching that exact size and an equal-or-higher load index and speed rating is a direct OEM-equivalent fit. Alternative sizes are acceptable only if the overall diameter stays within ±3% of OEM so the speedometer, ABS, and stability-control systems stay calibrated.

Sources: NHTSA — Tire Safety: Everything Rides on It

Reading 225/45R17 94H left-to-right: 225 is section width in millimeters, 45 is the aspect ratio (sidewall height as a percentage of width), R means radial construction, 17 is the rim diameter in inches, 94 is the load index (max ~1,477 lb per tire), and H is the speed rating (max sustained ~130 mph). The full code is standardized under DOT 49 CFR §571.109 (Federal Motor Vehicle Safety Standard 109) and ISO 4209.

Sources: ECFR — FMVSS 109 (49 CFR §571.109)

Yes, within limits. Plus-sizing (larger rim, lower-profile tire) is acceptable when overall diameter stays within ±3% of OEM, the load index meets or exceeds the original, and the wheel offset clears suspension and bodywork. Outside that envelope, the speedometer reads incorrectly, ABS and traction-control logic gets confused, and load capacity may drop below what the vehicle's GVWR requires — all of which can void warranties and create safety issues. Tire & Rim Association (T&RA) and ETRTO publish the engineering tables manufacturers use to verify these substitutions.

Sources: Tire & Rim Association (T&RA) — Standards

Replace tires when tread depth reaches 2/32" (the legal minimum in most U.S. states, marked by built-in wear bars in the tread grooves), or sooner — NHTSA wet-weather testing shows that braking distance roughly doubles between 4/32" and 2/32" on wet pavement. Replace immediately for any sidewall cut, bulge, puncture in the shoulder, or visible cord. Most tire manufacturers also recommend replacement after 6 years of service regardless of tread depth, and mandatory replacement at 10 years from the DOT date code (week/year stamped on the sidewall).

Sources: NHTSA — Tire Aging Research Program, USTMA — Tire Care Guide

Tread life ranges from about 25,000 to 80,000 miles depending on compound, vehicle, alignment, and driving style. Manufacturer treadwear warranties (commonly 40,000–80,000 miles) are pro-rated and require documented rotation every 5,000–7,500 miles. Independent of mileage, USTMA recommends a thorough inspection at 5 years from the DOT date code and replacement by 10 years regardless of remaining tread, because rubber compounds oxidize and lose flex strength over time.

Sources: USTMA — Tire Aging

On all-wheel-drive and full-time 4WD vehicles, yes — manufacturers typically require all four tires to be within 2/32" of each other to prevent driveline damage from differing rolling diameters. On front- or rear-wheel-drive vehicles, replacing in pairs (both fronts or both rears) is acceptable, and the new pair should be mounted on the rear axle regardless of drive layout — Michelin and Continental wet-handling research shows worn fronts under-steer predictably while worn rears can cause sudden over-steer in the wet.

Sources: Michelin — Why New Tires Go on the Rear

UTQG (Uniform Tire Quality Grading) is a three-part rating molded into the sidewall of every U.S. passenger tire, mandated by NHTSA under 49 CFR §575.104: Treadwear (a relative number — 300 means three times the reference tire's wear life in the government test), Traction (AA / A / B / C — wet-pavement skid grip), and Temperature (A / B / C — heat resistance at sustained high speed). UTQG is comparative within a brand and useful as a rough cross-brand indicator, but the test is run by each manufacturer, not by NHTSA, so cross-brand comparisons are imperfect.

Sources: NHTSA — UTQG Ratings Guide, ECFR — 49 CFR §575.104 UTQG

Load index is a coded number (typically 70–130 for passenger tires) corresponding to maximum load per tire — 94 = 1,477 lb, 100 = 1,764 lb, 109 = 2,271 lb. Speed rating is a letter (Q / S / T / H / V / W / Y / Z) for maximum sustained speed — H = 130 mph, V = 149 mph, W = 168 mph, Y = 186 mph. Both are mandated under FMVSS 119 and 139. Never fit a replacement tire with a lower load index or speed rating than OEM — the vehicle's brake-system tuning and stability calibration assume those minimums.

Sources: ECFR — FMVSS 139 (passenger tires)

The DOT code starts with the letters "DOT" followed by 8–13 characters, ending with a 4-digit week-and-year date — "2624" means the 26th week of 2024. NHTSA requires the date code on at least one sidewall (often only on the inboard sidewall — check both sides). Use it to verify a "new" tire isn't actually old warehouse stock; most chains will replace a tire dated more than 12 months before sale. The DOT code is also what NHTSA recall notices reference when a manufacturing-defect campaign is opened.

Sources: NHTSA — Tire Identification Number (TIN)

Not legally, but yes practically. Electric vehicles are 15–30% heavier than ICE equivalents of the same footprint (battery mass), deliver peak torque instantly, and demand low rolling resistance to preserve range. EV-specific tires (Michelin Pilot Sport EV, Continental EcoContact 6 Q, Pirelli P Zero Elect, Bridgestone Turanza EV) use reinforced sidewalls, higher load indexes (often XL or HL — Extra Load / High Load — per ETRTO 2021 spec), foam noise-insulating liners, and silica-heavy tread compounds. Fitting standard passenger tires to an EV typically reduces range 5–10% and shortens tread life by 30–50%.

Sources: Continental — Tires for Electric Vehicles, ETRTO — Standards Manual (load-capacity update for EVs)

Mount winter tires when daily average temperatures fall below 7°C (45°F) and remove them when they rise back above that for a sustained period. Below 7°C the rubber compound of all-season tires stiffens, dropping grip on dry pavement before snow or ice are even factors. Winter tires (marked with the 3-Peak Mountain Snowflake symbol, certified to ASTM F1805 traction performance) use softer compounds and biting edges that stay flexible to about −30°C but wear quickly in summer heat. Quebec and several U.S. mountain pass jurisdictions legally require winter tires from December to mid-March.

Sources: Transport Canada — Winter Tire Use in Canada, USTMA — Snow Tire Branding (3PMSF)

Standard M+S (Mud + Snow) all-seasons are adequate for occasional light snow and clear roads down to about freezing, but they don't meet the traction threshold for the 3-Peak Mountain Snowflake symbol — the actual cold-weather and packed-snow standard. "All-weather" tires (3PMSF-rated but designed to run year-round, e.g. Michelin CrossClimate 2, Nokian WR G4, Goodyear Assurance WeatherReady) are the middle ground: legal as winter tires in most jurisdictions, no seasonal swap required, but compromise about 10–15% of dry summer grip and 15–20% of deep-snow grip versus dedicated season-specific tires.

Sources: USTMA — Tire Types and Tread Design