How to Read the Numbers on a Tyre Sidewall

The sidewall of every tyre is packed with information — size, load rating, speed rating, age, construction, and whether it is a run-flat or reinforced tyre. Knowing how to read it means you can buy the correct replacement and understand what you are paying for.

This guide decodes everything written on a tyre sidewall, with a worked example. If you want us to look up the correct tyre for your car, call our mobile tyre fitting team on 01279 881234 with your registration.

The Tyre Size — Worked Example: 205/55 R16 91V

The main string of numbers and letters on the sidewall describes the tyre size. Here is what each part means for the common size 205/55 R16 91V.

205 — Tyre Width

The first number is the width of the tyre in millimetres across the tread, from sidewall to sidewall. 205 means the tyre is 205mm wide.

55 — Aspect Ratio (Profile)

The second number is the aspect ratio — the height of the sidewall as a percentage of the width. 55 means the sidewall height is 55% of 205mm, which is about 113mm. A lower number means a lower-profile tyre.

R — Construction

The letter R stands for radial construction, which is used on virtually all modern car tyres. You may occasionally see D (diagonal) or B (bias-belted) on specialist or vintage tyres.

16 — Rim Diameter

The last number in the size is the inner diameter of the tyre in inches — the wheel size the tyre fits. 16 means the tyre fits a 16-inch wheel.

91 — Load Index

The number after the size is the load index — the maximum weight each tyre can carry. 91 corresponds to 615kg. Higher numbers mean higher load capacity. See the load index table below.

V — Speed Rating

The final letter is the speed rating — the maximum sustained speed the tyre is designed for. V means up to 149mph. See the speed rating table below.

Speed Rating Guide

• T = 118mph
• H = 130mph
• V = 149mph
• W = 168mph
• Y = 186mph

It is legal to fit a tyre with a higher speed rating than originally specified, but not a lower one. Insurance policies can be invalidated by fitting under-rated tyres. See our UK tyre law guide.

Load Index — Common Values

• 84 = 500kg
• 87 = 545kg
• 91 = 615kg
• 94 = 670kg
• 98 = 750kg
• 99 = 775kg

Heavier vehicles and EVs need higher load indices. See our EV tyres guide for why load rating matters on electric cars.

The DOT Code and Tyre Age

The DOT code shows the tyre's age. It ends in a 4-digit number — the week and year of manufacture. "2319" means the 23rd week of 2019. See our tyre age guide for when to replace old tyres.

XL / Reinforced

"XL" (Extra Load) or "Reinforced" means the tyre has a higher load capacity than a standard tyre of the same size. These are often required on heavier vehicles, estates, SUVs and EVs. An XL tyre has a higher load index than the standard equivalent.

Run-Flat Indicators

Run-flat tyres are marked with one of several codes depending on the manufacturer:

• ROF or RFT — Goodyear / generic
• SSR — Continental
• DSST — Dunlop
• ZP — Michelin
• RSC — BMW system

Run-flats cannot be repaired after being driven flat. See our run-flat guide.

M+S and the Snowflake Symbol

• M+S (Mud and Snow) indicates a tyre with a tread pattern designed for mud and snow, but with no cold-weather compound guarantee
• The 3PMSF symbol (a snowflake inside a mountain) means the tyre has been tested and certified for severe snow performance — this is the proper winter/all-season mark

See our winter tyre guide for more.

Other Useful Markings

• DOT — the tyre meets US Department of Transportation standards
• E with a number — the tyre meets European ECE type approval
• TWI — Tread Wear Indicator location (small raised bars in the grooves at 1.6mm)

Not Sure What Size You Need?

Reading the sidewall is useful, but the easiest way to get the right tyre is to give us your registration number — we look up the correct size, load and speed rating for your exact car. Call 01279 881234 and we'll supply and fit the right tyres at your home or workplace anywhere across Essex, Hertfordshire and Cambridgeshire. See our all locations page for coverage.