Metric Tire Codes vs. Tire Load Index
Comparing 2 standards across 13 specifications. 13 key differences identified.
The ISO Metric Tire Code (standardized under ISO 4000-1 and ETRTO conventions, e.g. P225/45R17 91V) is the universal automotive tire sizing nomenclature. Decoding section width in millimeters, aspect ratio sidewall height percentage, internal radial carcass construction, wheel rim diameter in inches, load index, and maximum speed symbol.
The Tire Load Index (standardized under ISO 4000-1) is a numerical code assigned to a passenger or commercial tire indicating the maximum physical weight (in kilograms and pounds) the tire can carry when inflated to its maximum operating cold tire pressure. Spanning Load Index 70 (335 kg / 739 lb) to Load Index 120 (1400 kg / 3086 lb) per tire.
Specification Comparison Table
13 Parameters| Parameter / Spec | ||
|---|---|---|
|
Standardization
|
ISO 4000-1 / ETRTO (European Tyre and Rim Technical Organisation) / US Tire & Rim Association (TRA) | ISO 4000-1 / ETRTO / TRA Load Tables |
|
Prefix Designation
|
P: Passenger Car | LT: Light Truck (heavier plies) | ST: Special Trailer | T: Temporary Spare | — |
|
Section Width (e.g. '225')
|
Nominal cross-sectional tire width in millimeters from sidewall to sidewall (225 mm) | — |
|
Aspect Ratio / Profile (e.g. '45')
|
Sidewall section height expressed as a percentage of width (Height = 225 × 0.45 = 101.25 mm) | — |
|
Internal Construction (e.g. 'R')
|
R: Radial ply cord orientation (90° to travel) | D / B: Bias ply / belted bias (historic) | — |
|
Rim Diameter (e.g. '17')
|
Wheel rim bead seat diameter in whole inches (17.0 inches = 431.8 mm) | — |
|
DOT Date Code
|
4-digit oval stamp (e.g. '2422' = manufactured during the 24th week of 2022) | — |
|
Standard Load (SL) Pressure
|
— | Calibrated at 2.5 bar (36 psi) cold inflation pressure for passenger car tires |
|
Extra Load (XL / Reinforced)
|
— | Reinforced internal carcass calibrated at 2.9 bar (42 psi) for heavy electric vehicles (EVs) and SUVs |
|
Common Passenger Load Indices
|
— | LI 82: 475 kg (1,047 lb) | LI 88: 560 kg (1,235 lb) | LI 91: 615 kg (1,356 lb) | LI 95: 690 kg (1,521 lb) |
|
Heavy EV & SUV Load Indices
|
— | LI 100: 800 kg (1,764 lb) | LI 104: 900 kg (1,984 lb) | LI 108: 1,000 kg (2,205 lb) | LI 112: 1,120 kg (2,469 lb) |
|
Vehicle Axle Calculation
|
— | Sum of two tire load capacities on an axle must exceed the Gross Axle Weight Rating (GAWR) |
|
HL (High Load) EV Benchmark
|
— | New standard for heavy battery packs carrying higher load at equivalent tire volume and pressure |