Tire Sizing Guide

A tire sidewall, decoded.

Every tire's sidewall has a code that looks like 225/65R17 102H. Each number means something specific — here's the breakdown.

Section width — 225

The tire's width in millimetres, measured sidewall to sidewall when mounted on its design rim and inflated to spec. A 225 mm tire is wider than a 205 mm tire, but the actual contact patch depends on tread pattern, inflation, and load.

Aspect ratio — 65

Sidewall height as a percentage of section width. 65 means the sidewall is 65% of 225 mm = 146.25 mm tall. A lower aspect ratio (45, 40, 35) means a shorter sidewall — sportier handling but a harsher ride and more wheel damage from potholes.

Construction — R

R means radial (internal cords run perpendicular to direction of travel). Virtually every modern passenger tire is radial. You may occasionally see D (bias-ply, mostly trailer tires) or B (belted-bias, vintage).

Rim diameter — 17

The wheel diameter the tire is designed to mount on, in inches. A 17" tire mounts on a 17" wheel — they're not interchangeable. This is the number that connects your tire size to the wheel selection.

Load index — 102

A coded number indicating the maximum weight the tire can support. 102 = 850 kg per tire. Always match or exceed your vehicle's OE load index — going lower can void insurance and warranty. Common ranges: 91-95 for compact cars, 99-105 for sedans/SUVs, 110-120 for trucks.

Speed rating — H

Maximum sustained speed the tire is rated for:

• Q — 160 km/h (winter tires)
• S — 180 km/h
• T — 190 km/h
• H — 210 km/h (most all-season)
• V — 240 km/h
• W — 270 km/h (performance)
• Y — 300 km/h

When sizes get prefixed

Some sizes have a letter before the section width — most commonly P (P-metric, passenger car) or LT (light truck). LT tires have stiffer sidewalls and higher load capacity; don't fit them on a vehicle that calls for P-metric without a knowledgeable check.