Tyre Sidewall Markings Explained: What Every Number and Letter Means

# Tyre Sidewall Markings Explained: What Every Number and Letter Means

The sidewall of a tyre is packed with numbers, letters, and codes. Understanding them helps you buy the right replacement tyre and understand your vehicle's requirements.

Here is a complete guide to everything written on the sidewall of a modern tyre.

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The Main Size Code

Example: 205/55R16 91W

Width: 205

The first number is the tyre width in millimetres, measured across the widest point of the tyre when correctly inflated and fitted (not across the tread). In our example, the tyre is 205mm wide.

Aspect Ratio / Profile: 55

The second number is the aspect ratio — the sidewall height as a percentage of the width. In our example, the sidewall height is 55% of 205mm = 112.75mm.

Lower numbers (30, 35, 40) = lower profile, shorter sidewall, sportier feel but less cushioning. Higher numbers (60, 65, 70) = taller sidewall, more comfortable, better for rural roads.

Construction: R

The R stands for Radial construction — how the internal fabric cords run (perpendicular to the direction of travel). Virtually all modern passenger car tyres are radial. If you see a B, that indicates Bias-ply (crossply), found on older or specialist vehicles.

Rim Diameter: 16

The number after R is the wheel rim diameter in inches. This tyre fits a 16" wheel. Common sizes: 14", 15", 16", 17", 18", 19", 20", 21", 22".

Load Index: 91

The load index number indicates the maximum weight each tyre can carry at its rated maximum speed. In our example:

Load Index	Max load (kg)	Load Index	Max load (kg)
87	545	103	875
91	615	107	975
94	670	112	1,120
99	775	116	1,250
101	825	120	1,400

Never fit a tyre with a lower load index than specified by the manufacturer. This is illegal and dangerous. Fitting higher is always acceptable.

EVs and PHEVs often require a higher load index than the equivalent petrol car because of battery weight.

Speed Rating: W

The speed rating is the final letter. It indicates the maximum sustained speed the tyre is designed for:

Rating	Max speed
Q	100mph (160km/h)
R	106mph (170km/h) — common on vans/caravans
S	112mph (180km/h)
T	118mph (190km/h)
H	130mph (210km/h)
V	149mph (240km/h)
W	168mph (270km/h)
Y	186mph (300km/h)
Z	150mph+ (240km/h+)

You must fit a tyre with at least the speed rating specified by the manufacturer. Fitting a higher speed rating is fine (and common with performance upgrades).

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Special Markings

XL or EXL — Extra Load

Indicates a tyre with reinforced construction and higher load capacity than a standard tyre of the same size. XL tyres are often required by EVs and heavier cars to compensate for vehicle weight. They are run at slightly higher pressures than standard.

If your vehicle specifies XL tyres, always replace with XL. Fitting a standard (non-XL) tyre of the same size could result in inadequate load carrying.

RFT, ROF, RSC — Run-Flat Tyre

Indicates a run-flat tyre. These can support the vehicle for approximately 80km at 80km/h after losing air pressure. Required on vehicles without spare tyres (most BMWs, MINIs, and Mercedes).

MOE or MOExtended — Mercedes-Benz Run-Flat

Mercedes-specific run-flat designation. MOE tyres are approved and specification-compliant for Mercedes-Benz vehicles.

EMT — Extended Mobility Tyre

Bridgestone's run-flat designation. Used as original equipment on various vehicles.

FR — Flange Ridge

Indicates a raised protective rib on the lower sidewall that protects the wheel rim from kerbing damage.

MFS — Maximum Flange Shield

Similar rim protection feature to FR.

(*) — BMW Star Marking

A small star or asterisk indicates the tyre has been approved and optimised for BMW vehicles. BMW-star tyres may have specific noise, rolling resistance, or handling properties tuned for BMW models.

AO — Audi Original

Tyre approved as original equipment for Audi vehicles.

MO — Mercedes Original

Mercedes-approved original equipment tyre (different from MOE/MOExtended).

NO — Nissan Original

VOL — Volvo Original

XL FR MFS combinations

You may see multiple codes: e.g., 225/40R18 92Y XL FR. This means extra load construction with flange protection — a common specification for performance cars.

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The DOT Code

DOT followed by a series of letters and numbers is the US Department of Transportation code indicating the tyre was manufactured to US safety standards. This is required for all tyres sold in the UK.

The last four digits indicate manufacture date:

• Example: DOT XXXXXX 2619 = 26th week, 2019

See our [tyre age limit guide](/blog/tyre-age-limit-scotland) for what these dates mean for your safety.

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EU Tyre Label Ratings

Since 2012, all new tyres in Europe and the UK carry a label showing:

• Fuel efficiency: A (lowest rolling resistance) to G
• Wet grip: A (shortest stopping distance) to E
• External noise: measured in dB

These ratings are also typically printed on the tyre sidewall or packaging. Look for:

• A/A = excellent on both metrics (buy these)
• Never buy wet grip rating below C for normal Scottish road use

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Reading Your Current Tyres

If you are not sure what size or specification your vehicle needs:

1. Look on the driver's door sticker (inside the door frame)
2. Check the fuel cap sticker on some vehicles
3. Read the current tyre sidewall — if they were originally fitted, they are likely the correct size

Call 0141 266 0690 or [book online](/book) for expert advice on tyre specification and mobile fitting across Scotland.

[Tyre buying guide Scotland](/blog/tyre-buying-guide-scotland) | [Run-flat tyres Scotland](/blog/run-flat-tyres-scotland-guide) | [Tyre age limit Scotland](/blog/tyre-age-limit-scotland)