Tyre Size Explained: How To Read Your Tyre Markings
The numbers on your tyre sidewall look like a secret code — 205/55R16 91V. But each part means something specific. Here's how to decode it and why it matters when buying new tyres.
Breaking Down the Code: 205/55R16 91V
Let's take the most common tyre size in the UK as our example:
- 205 — Tyre width in millimetres. This is the distance across the tread from sidewall to sidewall. Common widths range from 155mm (small city cars) to 315mm (performance vehicles).
- 55 — Aspect ratio (profile). This is the height of the sidewall as a percentage of the width. A 55 profile means the sidewall height is 55% of 205mm = 112.75mm. Lower numbers mean a thinner sidewall (sportier, less comfortable). Higher numbers mean a taller sidewall (more comfortable, better pothole absorption).
- R — Radial construction. Virtually all modern car tyres are radial. You'll almost never see anything else.
- 16 — Wheel diameter in inches. This must match your wheel rim size exactly. Common sizes: 14" (small cars), 15–16" (family cars), 17–19" (SUVs and performance), 20"+ (luxury/sport).
- 91 — Load index. This indicates the maximum weight each tyre can support. 91 = 615 kg per tyre. Your replacement tyres must meet or exceed the original load index.
- V — Speed rating. The maximum speed the tyre is certified for. V = 149 mph. Common ratings: T (118 mph), H (130 mph), V (149 mph), W (168 mph), Y (186 mph). Your replacement tyres must meet or exceed the original speed rating.
Where to Find Your Tyre Size
Three places to look:
- On the tyre itself — the size is moulded into the sidewall in raised lettering. Look for the format XXX/XXRXX.
- Driver's door frame sticker — shows the factory-approved tyre size(s) along with recommended pressures.
- Vehicle handbook — lists all approved tyre sizes for your specific model and trim.
Can I Fit a Different Size?
In some cases, yes — but with important caveats. You can often go one size up or down in width (e.g., 205 to 215) as long as you adjust the profile to maintain the same overall diameter. This is called "plus sizing" when you increase width and decrease profile (for a sportier look/feel) or "comfort sizing" when you do the reverse.
However, you must never fit a tyre with a lower load index or speed rating than specified by your vehicle manufacturer. Doing so is illegal and invalidates your insurance. When in doubt, stick to the exact size on your door frame sticker.
Other Markings Worth Knowing
- DOT code (4 digits) — Manufacturing date. "2423" = week 24 of 2023. Important for checking tyre age.
- M+S or 3PMSF — Mud and Snow or Three Peak Mountain Snowflake symbols indicating winter/all-season capability.
- XL or Reinforced — Extra load tyre, capable of carrying more weight. Often required for heavier vehicles.
- Manufacturer markings — ★ (BMW), MO (Mercedes Original), AO (Audi Original), N0/N1 (Porsche). These indicate tyres developed specifically for that manufacturer.