Every tyre carries a string of numbers and letters on its sidewall that looks like a secret code. Understanding what these markings mean helps you order the correct replacement, compare prices accurately, and avoid dangerous mismatches. Here is the full breakdown.
A typical tyre size looks like this: 225/45 R17 94W. Each segment tells you something specific. The first number — 225 — is the tyre width in millimetres, measured from sidewall to sidewall. The second number — 45 — is the aspect ratio, or profile height. It is the sidewall height as a percentage of the width. A 45 profile means the sidewall is 45 percent of 225mm, or about 101mm.
The letter R stands for Radial, which describes the construction method. Almost all modern car tyres are radial, so you will almost always see an R here. The next number — 17 — is the wheel rim diameter in inches. This must match your wheel exactly.
The load index — 94 in our example — tells you the maximum weight each tyre can support. A load index of 94 equates to 670kg per tyre. Your car's manual specifies the minimum load index required. Using tyres with too low a load index is dangerous and illegal.
The speed rating — W in our example — indicates the maximum speed the tyre is designed for. W-rated tyres are safe up to 168mph. Common ratings include T (118mph), H (130mph), V (149mph), and Y (186mph). Again, your car's manual specifies the minimum required rating.
Additional markings include extra load (XL or Reinforced) for heavier vehicles, run flat (RFT, ZP, SSR, or specific brand codes), and directional arrows indicating which way the tyre must rotate. Winter tyres often carry a 3PMSF (Three Peak Mountain Snowflake) symbol, certifying winter performance.
If you are unsure about your tyre size, the easiest solution is to provide your vehicle registration number when ordering. At Tayside Mobile Tyres, we cross-reference your registration against the manufacturer database to confirm the exact specification. We then source and fit the correct tyres at your location, eliminating any guesswork.
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