Tyre Guide: Sizes, Types, Tread Depth and Replacement

Why Tyres Are Critical for Safety

Your tyres are the only part of your car that touches the road. Every action you take — accelerating, braking, steering, cornering — is transmitted through four patches of rubber, each roughly the size of a postcard. The condition of those patches determines how well your car responds.

Good tyres in the right condition provide:

• Grip — the friction that allows you to brake, steer, and accelerate without sliding
• Handling — predictable, responsive behaviour when cornering or changing direction
• Water dispersal — tread patterns channel water away from the contact patch to prevent aquaplaning
• Comfort — tyres absorb road imperfections and reduce noise

Worn, damaged, or incorrectly specified tyres compromise all of these. In wet conditions, the difference between 3mm and 1.6mm of tread can add several car lengths to your stopping distance. In an emergency, that difference can be the difference between stopping safely and a collision.

Tyres are also a legal matter. In the UK, driving with tyres below the legal minimum tread depth, with incorrect sizes, or with dangerous damage is a criminal offence. The penalty is up to £2,500 and three penalty points per tyre — so four illegal tyres could mean a £10,000 fine and 12 points (an automatic driving ban).

How to Read Tyre Size Markings

Every tyre has a series of numbers and letters moulded into the sidewall. A typical marking looks like this: 205/55 R16 91V. Here is what each part means:

205 — Section Width (mm)

The first number is the tyre's width in millimetres, measured from sidewall to sidewall. In this example, the tyre is 205mm wide. Wider tyres generally provide more grip but can increase fuel consumption and road noise.

55 — Aspect Ratio (Profile)

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

Lower profile tyres (e.g., 35 or 40) have shorter sidewalls. They offer sharper handling and a sportier look but ride more harshly and are more susceptible to damage from potholes. Higher profile tyres (e.g., 60 or 65) absorb more bumps and are common on comfort-oriented or off-road vehicles.

R — Construction Type

The letter R indicates radial construction, which is the standard for virtually all modern car tyres. Radial tyres have layers of fabric cord running at 90 degrees to the direction of travel, providing better grip, comfort, and longevity than older bias-ply designs.

16 — Rim Diameter (inches)

This is the diameter of the wheel rim the tyre is designed to fit, measured in inches. In this case, the tyre fits a 16-inch wheel. You must always match the tyre size to your wheel size — a tyre designed for a 16-inch rim cannot be fitted to a 17-inch wheel.

91 — Load Index

The load index is a code that corresponds to the maximum weight the tyre can support. A load index of 91 means the tyre can carry up to 615 kg. You can find load index lookup tables online or in your owner's manual.

You must never fit tyres with a lower load index than specified by the manufacturer. An underrated tyre could fail under the weight of the car, especially when fully loaded.

V — Speed Rating

The speed rating indicates the maximum speed the tyre is certified to sustain safely. Common ratings include:

Letter	Max speed
T	118 mph (190 km/h)
H	130 mph (210 km/h)
V	149 mph (240 km/h)
W	168 mph (270 km/h)
Y	186 mph (300 km/h)

You should always fit tyres with a speed rating equal to or higher than your car's top speed. Fitting lower-rated tyres is illegal and dangerous — they may not withstand the forces at higher speeds.

What Tyre Ratings Mean

Beyond size markings, tyres also carry an EU Tyre Label rating system (similar to energy labels on appliances). These labels rate three key attributes:

Fuel Efficiency (A to E)

This measures rolling resistance — how much energy the tyre wastes as it rolls. An A-rated tyre reduces fuel consumption compared to an E-rated tyre. Over the life of the tyre, this can save a meaningful amount of fuel.

Wet Grip (A to E)

This rates braking performance on wet roads. An A-rated tyre stops significantly shorter on a wet surface than an E-rated tyre. Wet grip is arguably the most important safety rating, particularly in the UK's frequently rainy climate.

Road Noise (measured in decibels)

This indicates the external noise the tyre produces. Lower decibel ratings mean quieter tyres. While this is less critical for safety, it affects comfort, especially on motorway journeys.

Types of Tyres Explained

Summer Tyres

Summer tyres are the default type fitted to most new cars in the UK. They are designed for temperatures above 7°C and offer:

• Excellent grip on dry and wet roads in warm conditions
• Good handling and responsive steering
• Lower rolling resistance (better fuel economy)

However, summer tyres lose grip significantly in cold weather. Below 7°C, the rubber compound hardens and provides less traction, particularly on icy or frosty roads.

Winter Tyres

Winter tyres are designed for temperatures below 7°C. They use a softer rubber compound that remains flexible in the cold and feature deeper tread patterns with sipes (tiny slits) that grip snow and ice.

Benefits include:

• Dramatically improved grip on cold, wet, icy, and snowy roads
• Shorter stopping distances in winter conditions
• Better traction when pulling away on slippery surfaces

In the UK, winter tyres are not legally required but are strongly recommended during the colder months (October to March), especially in Scotland and northern England. Many European countries mandate winter tyres during winter months.

All-Season Tyres

All-season tyres are a compromise between summer and winter tyres. They offer:

• Reasonable performance in both warm and cold conditions
• Convenience — no seasonal tyre swaps needed
• Adequate grip in light snow and frost

They do not match the outright performance of dedicated summer tyres in warm weather or winter tyres in severe cold, but for the UK's generally mild climate, they are an increasingly popular choice.

Run-Flat Tyres

Run-flat tyres have reinforced sidewalls that can support the car's weight even after a complete loss of pressure. After a puncture, you can typically continue driving at up to 50 mph for up to 50 miles — enough to reach a garage.

Advantages:

• No need for a spare wheel or emergency tyre repair kit
• You can continue driving safely after a puncture rather than being stranded

Disadvantages:

• Harsher ride quality due to stiffer sidewalls
• More expensive to buy and replace
• Cannot always be repaired after a puncture — they often need full replacement
• Must be fitted to cars equipped with a tyre pressure monitoring system (TPMS)

Legal Tread Depth in the UK

The law requires a minimum tread depth of 1.6mm across the central three-quarters of the tyre's width, around the entire circumference.

However, 1.6mm is the absolute legal minimum, not the point at which you should replace tyres. Safety organisations and tyre manufacturers recommend replacing tyres at 3mm, because:

• At 1.6mm, wet braking distances are significantly longer than at 3mm
• At 80 km/h on a wet road, a tyre with 1.6mm of tread takes approximately 11 metres longer to stop than one with 3mm
• Below 3mm, the tyre's ability to channel water decreases rapidly, increasing aquaplaning risk

Replacing at 3mm gives you a safety margin and ensures you never accidentally drop below the legal limit.

How to Measure Tread Depth

The 20p Coin Test

The simplest method is the 20p test:

1. Insert a 20p coin into the main tread grooves of the tyre
2. If the outer band of the coin is hidden by the tread, you have more than 1.6mm remaining
3. If you can see the outer band, the tread is too low and the tyre needs replacing

Check in at least three places across the width of the tyre and at several points around its circumference. Tyres do not always wear evenly.

Tread Depth Gauge

For a precise measurement, use a tread depth gauge (available for a few pounds from any motor factors). Insert the probe into the main groove, press the base flat against the tread surface, and read the measurement. Check at several points.

Tread Wear Indicators

All modern tyres have built-in tread wear indicators (TWIs) — small raised bars in the main grooves. When the tread surface wears down to the level of these bars, the tyre has reached 1.6mm and must be replaced.

Signs Tyres Need Replacing

Cracks in the Sidewall

Small cracks or crazing on the tyre's sidewall indicate the rubber is ageing and becoming brittle. This is common on older or infrequently driven cars. Cracked sidewalls can lead to sudden blowouts and the tyre should be replaced regardless of tread depth.

Bulges or Blisters

A bulge or blister on the sidewall means the internal structure has been damaged, usually from hitting a pothole or kerb. This weakens the tyre and it can blow out without warning. Replace immediately.

Uneven Wear

If the tread is wearing unevenly — more on one side than the other, or in the centre versus the edges — this indicates a problem:

• Worn on both edges: under-inflation — the tyre has been running with too little air pressure
• Worn in the centre: over-inflation — the tyre has been running with too much pressure
• Worn on one edge only: incorrect wheel alignment — the wheels are pointing slightly off-centre
• Patchy or cupped wear: worn suspension components (shock absorbers, springs, or bushes)

Uneven wear should be investigated and the cause corrected before fitting new tyres, otherwise the new tyres will wear the same way.

Vibration at Speed

If you feel vibration through the steering wheel or body at certain speeds, the tyres may be unbalanced, damaged, or have developed a flat spot (common after a car has been parked in one position for weeks or months).

When to Replace Tyres by Age

Even if the tread looks fine, tyre rubber degrades over time. UV light, ozone, temperature changes, and the chemical properties of rubber all cause gradual deterioration.

Industry guidance:

• Replace tyres after 5–6 years from the date of manufacture, regardless of tread depth
• Never use tyres older than 10 years, even if they appear to have plenty of tread

You can find the manufacture date on the tyre sidewall. Look for the DOT code — the last four digits indicate the week and year of manufacture. For example, 2321 means the tyre was made in week 23 of 2021.

Tyre Rotation and Alignment

Tyre Rotation

Front tyres wear faster than rears on most front-wheel-drive cars (which make up the majority of UK vehicles). Rotating tyres — swapping front and rear — every 6,000 to 8,000 miles helps ensure even wear across all four tyres and extends the overall life of the set.

Some tyre types (directional or asymmetric) can only be rotated front-to-rear on the same side. Check the tyre's sidewall markings for rotation instructions.

Wheel Alignment

Wheel alignment (also called tracking) ensures all four wheels are pointing in the correct direction. Misalignment causes:

• Uneven tyre wear
• The car pulling to one side
• Increased fuel consumption
• Less predictable handling

Alignment should be checked every 12 months, after hitting a significant pothole or kerb, or whenever new tyres are fitted. An alignment check typically costs £30 to £60, and a full four-wheel alignment costs £60 to £120.

Typical Tyre Replacement Costs

Tyre prices vary significantly by size, brand, and type:

Tyre category	Typical cost per tyre
Budget (e.g., Linglong, Sailun)	£40 – £70
Mid-range (e.g., Firestone, Hankook)	£60 – £110
Premium (e.g., Michelin, Continental, Pirelli)	£90 – £180+
Run-flat (any brand)	£100 – £250+
Winter tyres	£60 – £150+

These prices are for common sizes (195/65 R15 to 225/45 R17). Larger wheels, low-profile tyres, and performance specifications cost more.

Fitting and balancing are usually included in the price or cost an additional £10 to £15 per tyre. Disposal of the old tyre is typically included.

Saving Money on Tyres

• Compare prices from multiple fitters — online tyre retailers (e.g., Black Circles, mytyres) often offer competitive prices with fitting included at a local partner garage.
• Buy in pairs — replacing two tyres at a time (on the same axle) is standard practice and some fitters offer pair discounts.
• Consider mid-range brands — they often offer 90% of the performance of premium tyres at 60% of the price.
• Check for seasonal offers — many fitters run promotions in spring and autumn when drivers switch between summer and winter tyres.

Your tyres are a critical safety component and not the place to cut corners. Budget tyres from reputable brands are fine; unknown, ultra-cheap imports with no EU tyre label should be avoided.