Understanding Tire Sidewall Markings: 225/45R17 91V, DOT Codes, Load Index, Speed Rating, UTQG Decoded

The Sidewall: Your Tire's Birth Certificate

A tire sidewall is dense with alphanumeric codes — every marking communicates a specific engineering specification or regulatory requirement. Understanding these codes enables you to buy the right replacement tires, verify tire age, and confirm load and speed suitability for your vehicle.

Tire Size: 225/45R17 91V

This is the universal tire size format. Let's decode each element using a common performance tire size:

225 — Section Width (mm)

The tire's section width in millimeters, measured from the widest point of the outer sidewall to the widest point of the inner sidewall (not the tread width) when mounted on the specified rim width. In this example, the tire is 225mm wide (approximately 8.9 inches).

Real-world section widths vary slightly based on the rim width the tire is mounted on. A 225mm tire on a 7.5-inch rim will measure slightly wider than the same tire on a 7-inch rim.

Common section widths: 195mm (economy cars), 205-215mm (compact cars), 225-235mm (mid-size sedans), 245-265mm (sports cars and sport sedans), 275-315mm (supercars and trucks).

45 — Aspect Ratio (%)

The sidewall height expressed as a percentage of the section width. In this example, 45 means the sidewall height is 45% of 225mm = 101.25mm (approximately 4.0 inches).

Lower aspect ratios (35, 40, 45) mean shorter, stiffer sidewalls: sharper steering response, harsher ride quality, greater vulnerability to pothole damage. Higher aspect ratios (55, 60, 65, 70) mean taller, more compliant sidewalls: softer ride, better pothole absorption, less precise steering.

R — Construction Type

"R" stands for Radial construction — the standard for all passenger car tires manufactured since the 1980s. Radial tires have body plies running perpendicular to the direction of travel (radially around the tire), with steel belts under the tread for strength. "D" indicates diagonal/bias-ply construction (still used on some trailer tires and heavy equipment). "B" indicates bias-belted (belted bias-ply).

17 — Rim Diameter (inches)

The diameter of the wheel the tire is designed to mount on, in inches. Common sizes: 15-17 inches (economy and compact cars), 17-19 inches (mid-size and sport sedans), 20-22 inches (luxury SUVs and trucks). Rim diameter must match exactly — a 225/45R17 tire will not physically mount on a 16-inch or 18-inch wheel.

91 — Load Index

A numerical code that specifies the maximum load the tire can carry when inflated to its maximum pressure. The "91" corresponds to 615 kg (1,356 lbs) per tire.

Load Index	Max Load (lbs)	Max Load (kg)	Typical Application
87	1,201	545	Subcompact cars (Honda Fit)
91	1,356	615	Compact cars (Honda Civic, Toyota Corolla)
94	1,477	670	Mid-size sedans (Toyota Camry, Honda Accord)
98	1,653	750	Crossovers (Honda CR-V, Toyota RAV4)
102	1,874	850	Full-size sedans, small SUVs
108	2,205	1,000	Full-size SUVs (Toyota Highlander)
114	2,601	1,180	Heavy SUVs (Ford Expedition)
120	3,086	1,400	Light trucks, heavy SUVs
126	3,748	1,700	Heavy-duty trucks

The total load capacity of all four tires must exceed the vehicle's gross vehicle weight rating (GVWR).

V — Speed Rating

A letter code indicating the maximum sustained speed the tire is certified for under laboratory test conditions (note: this is a test standard, not a recommendation to drive at this speed).

Rating	Max Speed (mph)	Max Speed (km/h)	Typical Application
S	112	180	Economy cars, minivans
T	118	190	Family sedans, many all-season tires
H	130	210	Standard for most modern sedans and touring tires
V	149	240	Sport sedans, performance touring
W	168	270	High-performance cars
Y	186	300	Ultra-high-performance and exotic cars
(Y)	186+	300+	Specialized supercar tires

The replacement tire's speed rating must equal or exceed the vehicle's factory tire specification. Installing a lower speed rating (e.g., H-rated tires on a vehicle that came with V-rated tires) is a safety liability and may void insurance coverage in some jurisdictions.

DOT Code: Manufacturing Date

The Department of Transportation (DOT) code includes the tire's serial number, manufacturer code, and — critically — the date of manufacture in the final four digits:

DOT U2LL LMLR 3223 — The last four digits "3223" mean this tire was manufactured in the 32nd week of 2023 (August 7-13, 2023).

DOT CXAP 4519 — Manufactured in the 45th week of 2019 (early November).

DOT ABC 126 — A three-digit code means the tire was manufactured before 2000, and must be replaced immediately. These tires are at minimum 26 years old.

Always check the DOT date when buying new tires, especially from online retailers or discount warehouses. Tires that have been sitting in a warehouse for 2-3 years are still safe (rubber aging accelerates once mounted and exposed to UV and ozone), but always confirm the age before installation.

UTQG Ratings (Uniform Tire Quality Grading)

The U.S. Department of Transportation requires UTQG ratings on all passenger car tires (except winter tires, deep-tread light truck tires, and temporary spares). Ratings are self-certified by the manufacturer, and there is NO independent government verification — use UTQG as a rough guideline, not a precision measurement.

Treadwear (e.g., 400)

A comparative number representing the tire's wear rate. A tire graded 200 would wear approximately twice as long as a tire graded 100 under the specified test conditions — but this is NOT linear or uniform across brands. A Michelin rated at 500 and a Kumho rated at 500 may have different real-world tread life due to the self-certification process.

Treadwear Rating	Typical Tire Category	Approximate Mileage Expectation
100-200	Extreme performance summer tires	15,000-25,000 miles
200-300	Ultra-high-performance tires	25,000-40,000 miles
300-500	Standard all-season touring	40,000-65,000 miles
500-700	Long-wearing touring tires	60,000-85,000 miles
700+	Maximum tread life tires	80,000-100,000 miles

Traction (e.g., AA, A, B, C)

Wet coefficient of friction measured on asphalt and concrete surfaces. AA is the highest rating; C is the lowest permissible.

Temperature (e.g., A, B, C)

Resistance to heat buildup at high speed. A is the highest rating; C is the minimum required.

Additional Markings to Know

• M+S: Mud and Snow rated. Indicates a tread pattern with some winter capability. Does not necessarily indicate 3PMSF certification.
• 3PMSF (3-Peak Mountain Snowflake): Winter performance certification. Meets minimum snow traction standards. Required for winter tires in some jurisdictions.
• Rotation arrow: Directional tires only. Indicates required rolling direction.
• INSIDE / OUTSIDE: Asymmetric tires only. Must be mounted with the correct face outward.
• Max Load XXX lbs / Max Press XX PSI: The tire's maximum structural limits. NOT the recommended operating pressure.
• Plies: Number and material of tire layers ("Tread: 2 polyester + 2 steel + 1 nylon").
• E-mark: European Economic Commission approval number, required for tires sold in the EU.

Conclusion

Every marking on a tire sidewall serves a specific engineering or regulatory purpose. For purchasing decisions, focus on: size (must match factory spec exactly), load index (must meet or exceed factory spec), speed rating (must meet or exceed factory spec), and DOT date code (prefer tires manufactured within the last 2 years). Use UTQG ratings as a comparative guide within the same brand, but do not rely on them for cross-brand comparisons. When in doubt, the tire information placard on your driver's door jamb lists the factory specifications — match these numbers and you cannot go wrong.