How to Read Your Tyre Size: A Plain-English Guide

By Salek Tyre & Mechanic · Ashford, TW15

Every tyre has a code on the sidewall — something like 205/55 R16 91V. It looks complicated but it's straightforward once you know what each part means. Here's what it all says, explained in plain English.

Where to find your tyre size

Look at the sidewall of any tyre already on your car — the code is moulded into the rubber in large print. You can also find the recommended size on a sticker inside the driver's door jamb, in the fuel filler flap, or in your owner's manual. All four tyres should normally be the same size.

Breaking down 205/55 R16 91V

205 — Width (in millimetres)

The first number is the tyre's width, measured across the tread from sidewall to sidewall in millimetres. A 205mm tyre is 205mm wide. Common widths for everyday UK cars range from around 175mm to 255mm. Wider tyres generally offer more grip but cost more and can affect fuel economy.

55 — Aspect ratio (profile height as a % of width)

This number is the height of the tyre's sidewall expressed as a percentage of its width. A 55 profile means the sidewall height is 55% of 205mm — about 113mm. Lower numbers (e.g. 35, 40, 45) mean a lower-profile, sportier-looking tyre. Higher numbers (65, 70) mean a taller sidewall, which typically gives a softer ride.

R — Radial construction

The letter R stands for Radial, meaning the tyre's internal cords run radially from bead to bead. Almost every modern tyre on a standard car is radial — this part of the code is rarely a decision point.

16 — Rim diameter (in inches)

This tells you the diameter of the wheel the tyre fits, measured in inches. A 16 means the tyre fits a 16-inch diameter wheel rim. This must match your wheels exactly — fitting a 17-inch tyre on a 16-inch rim is physically impossible.

91 — Load index

The load index is a number that corresponds to the maximum weight each tyre can carry. 91 means each tyre can support up to 615kg. You must never fit a tyre with a lower load index than recommended for your vehicle — check your owner's manual or the door sticker for the minimum rating.

V — Speed rating

The speed rating is the maximum sustained speed the tyre is designed for. V means up to 240 km/h (149 mph). For most UK driving this makes little practical difference, but again you should not fit a tyre with a lower speed rating than recommended for your car.

Other markings you might see

XL or Extra Load

XL (or "Reinforced") means the tyre is built to carry a heavier load than a standard tyre of the same size. Some modern cars — particularly those that originally came fitted with run-flat tyres — require XL-rated replacements. If your car requires XL, fitting a standard tyre is unsafe.

Run Flat (RF, ROF, SSR, DSST)

Different manufacturers use different abbreviations but they all mean the same thing — the tyre can be driven on for a limited distance (typically 50 miles at up to 50 mph) after a puncture. See our guide: What are run-flat tyres?

The manufacture date (e.g. 2524)

A four-digit code on the sidewall tells you when the tyre was made. The first two digits are the week, the last two are the year. "2524" means week 25 of 2024. Tyres degrade with age even if they have plenty of tread — have them checked once they're 5 years old.

How to order the right tyres

When calling a garage or ordering online, you just need to quote the three main numbers from the sidewall — for example: "205/55/16". We'll confirm the load and speed rating from your car's specification. If you're unsure, just give us a call and we'll look it up for you.