Metric Tire Codes vs. Tire Speed Ratings
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 Speed Ratings (standardized under ISO 4000-1 and ECE Regulation 30) are alphabetical index symbols indicating the maximum sustained velocity a tire can safely maintain under its rated load capacity. Ranging from Q (160 km/h / 99 mph) for dedicated winter tires to V (240 km/h), W (270 km/h), Y (300 km/h), and (Y) (>300 km/h / >186 mph) for hypercars.
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 / UN ECE R30 / SAE J1561 |
|
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) | — |
|
Q Rating
|
— | 160 km/h (99 mph) — Studded and studless Nordic winter tires |
|
S & T Ratings
|
— | S: 180 km/h (112 mph) | T: 190 km/h (118 mph) — Standard family sedans, minivans, and all-season tires |
|
H Rating (High Speed)
|
— | 210 km/h (130 mph) — Touring sedans and premium crossovers |
|
V Rating
|
— | 240 km/h (149 mph) — Sport compacts and performance GT cars |
|
W & Y Ratings
|
— | W: 270 km/h (168 mph) | Y: 300 km/h (186 mph) — Exotic sports cars and track-focused performance vehicles |
|
(Y) In Parentheses
|
— | Speeds in excess of 300 km/h (>186 mph) — Certified individually with vehicle manufacturer for hypercars (Bugatti, Koenigsegg, Porsche GT3 RS) |