Metric Tire Codes vs. Wheel Offset
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.
Wheel Offset (denoted as ET from the German 'Einpresstiefe', measured in millimeters) is the distance from the wheel's true centerline to the mounting hub face. Dictating whether wheels tuck inside fenders (Positive ET), sit centered (Zero ET), or poke outwards (Negative ET), offset directly controls suspension scrub radius, steering stability, and brake caliper clearance.
Specification Comparison Table
13 Parameters| Parameter / Spec | ||
|---|---|---|
|
Standardization
|
ISO 4000-1 / ETRTO (European Tyre and Rim Technical Organisation) / US Tire & Rim Association (TRA) | — |
|
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) | — |
|
Definition of Offset (ET)
|
— | Distance in millimeters from the physical geometric centerline of the wheel width to the mounting hub contact face |
|
Positive Offset (+ET, e.g. ET+45)
|
— | Hub face is located toward the outer street-facing side of the wheel (standard on front-wheel drive and modern AWD cars) |
|
Zero Offset (ET0)
|
— | Hub mounting face aligns exactly with the true centerline of the wheel width |
|
Negative Offset (-ET, e.g. ET-12)
|
— | Hub face is recessed toward the back/suspension side, pushing the wheel outwards into a deep-dish stance (lifted 4x4 trucks) |
|
Scrub Radius Impact
|
— | Decreasing positive offset pushes wheels outwards and creates positive scrub radius (increases steering kickback and torque steer) |
|
Brake Caliper Clearance (X-Factor)
|
— | Spoke curvature independent of ET that clears large Brembo multi-piston fixed brake calipers |