Tyre Size Guide - How to Read Sizes & Match Them to Wheels

Reading the size

Every tyre size follows the same code. Take 265/60R18: 265 is the tread width in millimetres. 60 is the aspect ratio — the sidewall is 60% of the width, so 159 mm tall. R means radial. 18 is the wheel diameter it fits, in inches. After the size you'll see something like 114H — the load index (114 = 1,180 kg per tyre) and speed rating (H = 210 km/h).

Matching tyre width to wheel width

Ranges are general guidance — the tyre manufacturer's approved rim widths for each size govern. We match this for you on every wheel-and-tyre order.

Too narrow a tyre on a wide rim stretches the sidewall (looks aggressive, compromises the bead); too wide bulges and squirms. Mid-range keeps the tyre working the way its engineers intended.

Upsizing wheels? Keep the overall diameter

When you move from an 18" to a 20" wheel, the tyre's sidewall must shrink so the overall rolling diameter stays within about 3% of factory — otherwise your speedometer, gearing and safety systems drift. Example: a factory 265/60R18 (≈775 mm tall) plus-sizes cleanly to a 265/50R20 (≈773 mm) — near-identical diameter, bigger wheel.

The full mathematics — and what happens to your speedo when you get it wrong — is covered in our speedometer variance guide.