Metric Tire Codes vs. TPMS & Valve Stems
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.
Tire Pressure Monitoring Systems (TPMS, mandated by the US TREAD Act and EU UNECE Regulation 64) utilize Direct TPMS wheel-mounted valve sensors communicating via RF radio frequencies (315 MHz in North America, 433.92 MHz in Europe and Global). Utilizing the standard Schrader pneumatic valve with unified 8V1-32 UNEF cap threads.
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) | — |
|
Pneumatic Valve Standard
|
— | Schrader automotive tire valve (standard TR413 / TR414 rubber snap-in or metal clamp-in) |
|
Valve Thread Specification
|
— | 8V1-32 UNEF (0.305 in / 7.7 mm diameter with 32 threads per inch) |
|
North American TPMS Frequency
|
— | 315 MHz UHF radio frequency (FCC Part 15 compliant) |
|
European & Global TPMS Frequency
|
— | 433.92 MHz UHF radio frequency |
|
Direct vs Indirect TPMS
|
— | Direct: Physical pressure sensor in each wheel | Indirect: ABS/ESP wheel speed sensors calculate rolling circumference drops |
|
TPMS Warning Threshold
|
— | Mandated dash warning triggers when pressure drops 25% below the placard recommended cold pressure |