How to Find Your Tyre Size: A Simple Guide for UK Drivers (Sidewall & Door Frame)

Why the correct tyre size matters

Your tyre size is not just a shopping detail—it affects speedometer accuracy, load capacity, grip, and clearance within the wheel arch. Fitting an incorrect size can invalidate insurance assumptions and create MOT-related issues if the combination is unsuitable for the vehicle.

When you book mobile tyre fitting, giving the right size upfront helps the technician bring the correct stock and avoid a wasted visit. This guide shows you two reliable places to find your size: the tyre sidewall and your vehicle documentation.

Reading the sidewall: what the numbers mean

Look at the side of your tyre. You will usually see a string similar to: 225/45 R17 94W.

225 — Section width in millimetres (tyre width across the tread).
45 — Aspect ratio: the sidewall height as a percentage of the width. Lower numbers mean a “lower profile” tyre.
R — Radial construction (almost all modern car tyres).
17 — Rim diameter in inches.
94 — Load index (weight capacity code).
W — Speed rating (maximum speed the tyre is designed for under load).

When you quote a size for a booking, read it exactly as printed, including load and speed symbols if asked. Some vehicles require specific load indices—especially SUVs, vans, and performance cars.

Check your door pillar or fuel flap sticker

Many vehicles have a manufacturer placard on the driver’s door frame (or inside the fuel filler flap) showing recommended tyre sizes and pressures. This is useful when:

Your current tyres are not original and you want to confirm what the maker intended.
You run winter and summer sets and want to match OEM guidance.
You are unsure whether your car has optional wheel sizes from the factory.

Your owner’s handbook remains the authoritative source if anything conflicts.

Run-flat tyres and unusual markings

Some tyres include extra markings (e.g. run-flat symbols, XL for extra load, or manufacturer-specific codes). If you are unsure, photograph the full sidewall text and send it when you book—mobile fitters can confirm compatibility with your vehicle registration.

Quick checklist before you call or book online

Note all numbers and letters from the sidewall of the tyre you want replaced (or all four if changing a set).
Confirm whether you need same axle pairs replaced together (often recommended for grip and wear).
Mention locking wheel nut key location if applicable.
If you have modified wheels, say so—offset and width can matter for clearance.

How Mobile Tyre Pro uses this information

When you provide your registration, postcode, and tyre size, we can route the right technician and stock for your job. Accurate sizing means faster turnaround and fewer surprises on the day—whether you are at home in Essex or stuck near a retail park in Suffolk.

If you are still unsure after checking the sidewall, contact us—we would rather clarify once than send the wrong specification. Safe, correctly sized tyres are non-negotiable for every job we attend.