Buying Guide
How to Read Your Tire Size
Oct 15, 2024 · 8 min read
Every tire sidewall carries a code that tells you its width, profile, rim diameter, and speed rating. Here is how to decode it in under a minute.
A tire size such as 225/45R17 94W looks cryptic, but each block of characters answers one simple question about the tire. Once you know the pattern you can read any sidewall in seconds and order replacements with total confidence.
225 - Section width
The first three digits are the width of the tire in millimetres, measured from sidewall to sidewall on the correct rim. A wider tire puts more rubber on the road, which usually improves dry grip but can increase road noise and fuel consumption.
45 - Aspect ratio
The two digits after the slash are the sidewall height expressed as a percentage of the section width. On a 225/45 tire the sidewall is 45% of 225 mm, so roughly 101 mm tall. A lower number means a shorter, stiffer sidewall: sharper steering, firmer ride.
R17 - Construction and rim diameter
R stands for radial construction, which is what almost every modern road tire uses. The number after it is the wheel diameter in inches that the tire is designed to fit. This number must match your wheel exactly.
W - Speed rating and performance certification
The letter is the certified speed rating: W is certified up to 168 mph, Y up to 186 mph. Never fit a tire with a lower speed rating than your vehicle handbook specifies.
Where to find it
Check the sidewall of your current tires first. You will also find the recommended sizes on a placard inside the driver's door jamb, inside the fuel filler flap or in the owner's manual.
