How to Read a Tyre Sidewall: Decoding the Numbers

Take a typical tyre marking: 205/55 R16 91V. The first number, 205, is the tyre width in millimetres measured across the widest point of the inflated tyre. The second number, 55, is the aspect ratio — the height of the tyre's sidewall expressed as a percentage of its width. So a 55 profile means the sidewall height is 55% of 205mm, which is about 112mm.

The R stands for radial construction — the way the internal cords of the tyre run. Virtually all modern car tyres are radial. The 16 is the rim diameter in inches — the size of the wheel the tyre fits. Always match this to your wheel size exactly.

The 91 is the load index — a code that represents the maximum weight each tyre can carry. A load index of 91 corresponds to 615kg per tyre, so four tyres can support up to 2,460kg of vehicle weight. Never fit a tyre with a lower load index than your vehicle requires — check your owner's manual for the minimum specification.

The V is the speed rating — the maximum sustained speed the tyre is designed for. V-rated tyres are good to 149mph. Other common ratings include T (118mph), H (130mph), W (168mph), and Y (186mph). Again, never fit tyres with a lower speed rating than your car requires.

The DOT code gives you the tyre's date of manufacture — the last four digits are the week and year (e.g., 2224 = 22nd week of 2024). XL or REINF indicates a reinforced tyre with higher load capacity. M+S (mud and snow) indicates the tyre has some winter capability, though it's not the same as a full winter tyre. The three-peak mountain snowflake symbol (3PMSF) means the tyre meets proper winter tyre performance standards.

Some tyres also carry manufacturer-specific markings. BMW's run-flat tyres are marked RFT or RSC. Tyres approved for Mercedes are marked MOE. Porsche-approved tyres carry N0, N1, N2 markings. These indicate the tyre has been specifically tested and approved for use on that manufacturer's vehicles.