Decoding the Numbers on Your Tyre Sidewall
Every tyre has a sequence of numbers and letters on the sidewall that tells you exactly what type of tyre it is. For example: 205/55 R16 91V. Let's break this down. The first number — 205 — is the tyre width in millimetres, measured from sidewall to sidewall. The second number — 55 — is the aspect ratio, the height of the sidewall as a percentage of the width. So a 55 series tyre has a sidewall height of 55% of 205mm, which is approximately 113mm.
The letter R indicates the tyre is of radial construction — virtually all modern tyres are radial. The number 16 is the diameter of the wheel rim in inches that the tyre is designed to fit. This is arguably the most critical dimension — fitting a tyre to the wrong rim diameter is impossible.
Load Index and Speed Rating
The number after the rim diameter — 91 in our example — is the load index. This is a code that refers to the maximum load the tyre can carry. Load index 91 means a maximum of 615kg per tyre. Never fit a tyre with a lower load index than specified for your vehicle.
The final letter — V — is the speed rating. This indicates the maximum sustained speed the tyre is rated for. V = up to 149mph. Common speed ratings include T (118mph), H (130mph), V (149mph), W (168mph), and Y (186mph+). Again, never fit a tyre with a lower speed rating than your vehicle requires.
Finding the Right Tyre Size for Your Car
Your vehicle's correct tyre size is listed in the owner's manual and on a sticker inside the driver's door jamb. Some vehicles can accept multiple sizes (staggered fitments on sports cars, for example). When you book with Slick Mobile Tyres, simply give us your vehicle registration and we'll identify the correct size automatically.
- Width: mm (e.g., 205)
- Aspect ratio: % of width (e.g., 55)
- Rim diameter: inches (e.g., 16)
- Load index and speed rating must meet vehicle specs