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How to Read Tyre Size (With Examples for UK Drivers)
Have you ever looked at the side of your tyre and wondered what all those numbers and letters mean? For example: 225/45 R17 94W.
Understanding your tyre size is essential — especially when buying tyres online. The wrong size can affect safety, fuel efficiency, handling, and even your MOT result.
If you're in Park Royal, Wembley, Ealing, Acton, Willesden, or Harlesden, this simple guide will help you understand tyre sizes with confidence.
At www.parkroyaltyres.co.uk, you can search by tyre size or vehicle registration number to instantly find the correct tyres for your car.
Where Do You Find Your Tyre Size?
Your tyre size can usually be found:
- On the sidewall of your current tyre
- Inside the driver’s door frame
- In your vehicle handbook
- On the inside of the fuel cap (on some cars)
The size appears as a series of numbers and letters, such as:
225/45 R17 94W
Let’s break it down.
Breaking Down a Tyre Size – Step by Step
Using the example: 225/45 R17 94W
225 – Tyre Width (in Millimetres)
The first number represents the tyre width.
225 = 225mm wide (from one sidewall to the other).
A wider tyre:
- Provides better grip
- Improves stability
- May slightly increase fuel consumption
A narrower tyre:
- May improve fuel efficiency
- Can perform better in snow
45 – Aspect Ratio (Sidewall Height)
The second number is the aspect ratio.
45 means the sidewall height is 45% of the tyre width.
For 225/45:
45% of 225mm = sidewall height
Lower aspect ratio (e.g., 40):
- Sportier handling
- Lower-profile appearance
- Firmer ride
Higher aspect ratio (e.g., 60):
- More comfort
- Better cushioning
- Softer ride
R – Radial Construction
The letter R stands for Radial.
Almost all modern tyres are radial. They offer:
- Better road contact
- Improved durability
- Enhanced fuel efficiency
17 – Wheel Diameter (in Inches)
The number after the R indicates the wheel diameter.
17 = 17-inch wheel
This must match your wheel size exactly. If your wheels are 17 inches, you must use tyres designed for 17-inch rims.
94 – Load Index
The load index shows how much weight each tyre can safely carry.
94 corresponds to a specific maximum weight rating.
Your vehicle manufacturer sets the minimum required load rating. Using a lower load index than recommended can:
- Compromise safety
- Cause MOT failure
- Lead to tyre damage
W – Speed Rating
The final letter represents the speed rating.
W = rated up to 168mph (270 km/h)
You don’t need to drive at that speed — but you must meet or exceed your vehicle’s required speed rating.
Common UK speed ratings:
- H – Up to 130mph
- V – Up to 149mph
- W – Up to 168mph
- Y – Up to 186mph
Real-Life Examples for UK Drivers
Common tyre sizes seen in NW London include:
- 205/55 R16 – Popular on hatchbacks
- 225/45 R17 – Common for executive cars
- 225/40 R18 – Sport models
- 245/40 R18 – Larger saloons
If you're unsure of your tyre size, you can search using your vehicle registration number online.
Can You Change Tyre Size?
You should only change tyre size if:
- It is manufacturer-approved
- The rolling diameter remains correct
- Load and speed ratings match requirements
Incorrect tyre size can cause:
- Inaccurate speedometer readings
- Poor fuel efficiency
- Handling problems
- MOT failure
Always consult experts before changing sizes.
What If You Have Run-Flat Tyres?
Some vehicles are equipped with run-flat tyres, allowing limited driving after a puncture.
If your car currently uses run-flats, switching to standard tyres may require adjustments. We can advise you on the safest option.
Professional Tyre Fitting in Park Royal
Visit us at:
Unit 4 Unimix House, Abbey Road, Park Royal, London, NW10 7TR
Garage Hours:
Mon – Sat: 08:00 – 20:00
Sun: 10:00 – 18:00
We provide:
- Expert tyre fitting
- Computerised wheel balancing
- Hunter Wheel Alignment
- Pressure checks
Proudly serving Park Royal, Wembley, Ealing, Acton, Willesden and Harlesden.
24-Hour Mobile Tyre Service
Flat tyre and unsure about your size?
Call: 07476 586 589
Our mobile vans operate across Park Royal, Wembley, Ealing, Acton, Willesden, Harlesden and surrounding areas. We dispatch the nearest technician to reach you quickly.
- Emergency tyre replacement
- Home fitting
- Workplace fitting
- Fast response
No guessing — we bring the correct tyre to you.
Why Knowing Your Tyre Size Matters
Understanding tyre size helps you:
- Avoid buying the wrong tyres
- Save time when booking online
- Stay road legal
- Improve vehicle performance
- Avoid unnecessary costs
It gives you peace of mind when replacing tyres.
Ready to Find the Right Tyres?
You now know how to read tyre sizes — finding the correct tyres is easy.
Contact Park Royal Tyres Today
Phone: 020 3886 2355
Email: info@parkroyaltyres.co.uk
Address: Unit 4 Unimix House, Abbey Road, Park Royal, London, NW10 7TR
Serving Park Royal, Wembley, Ealing, Acton, Willesden & Harlesden.
Know your size. Choose the right tyres. Drive safely with Park Royal Tyres.
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