A typical tyre marking looks something like 205/55 R16 91V. The first number — 205 — is the tyre width in millimetres. The second number — 55 — is the aspect ratio, which is the height of the tyre sidewall expressed as a percentage of the width. R indicates radial construction, and 16 is the rim diameter in inches. These three figures together tell you what size tyre will fit your wheel.
The number 91 is the load index, indicating the maximum weight each tyre can support at its rated pressure. Every load index number corresponds to a specific weight — 91 equates to 615kg per tyre. Never fit a tyre with a lower load index than your vehicle manufacturer specifies. The letter V is the speed rating, indicating the maximum speed the tyre is designed to sustain. V-rated tyres are approved for speeds up to 240 km/h.
When ordering replacement tyres, always match all four values — width, aspect ratio, rim diameter and speed/load rating — to what is currently on your vehicle. Fitting the wrong size can affect speedometer accuracy, handling and even your insurance validity. If you are ever unsure about which tyre is right for your car, the team at Royal Mobile Tyres Cardiff is happy to advise and fit the correct tyres at your home or workplace.