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Understanding Tyre Size Markings
The long code printed on your tyre sidewall is not random — it describes exactly how the tyre is built and what it can safely handle.
A typical example looks like this:
205/55 R16 91V
This tells you the tyre’s:
- Width
- Sidewall height (profile)
- Construction type
- Wheel size
- Weight capacity
- Maximum speed capability
You should always match or exceed the tyre size, load index and speed rating listed in your vehicle handbook or door sticker. If unsure, a professional fitter like GForce Tyres can confirm the correct specification.
Let’s break the code down properly.
The Sidewall Code Explained
Example: 205/55 R16 91V
| Part | Meaning |
|---|---|
| 205 | Tyre width in millimetres |
| 55 | Aspect ratio (profile) |
| R | Radial construction |
| 16 | Wheel diameter (inches) |
| 91 | Load index |
| V | Speed rating |
Once you understand this pattern, you can read almost any tyre size.
Tyre Width Explained
The first number shows the tyre’s width in millimetres.
205 = approx 205 mm wide
How width affects driving
Wider tyres (225–235)
- More dry grip
- Sportier handling
- Slightly higher fuel consumption
- More sensitive to standing water
Narrower tyres (185–195)
- Better in rain & snow
- Quieter ride
- Improved fuel economy
- Less dry grip
The printed width is always your starting point when choosing replacement tyres.
Aspect Ratio (Tyre Profile)
The second number shows the sidewall height as a percentage of width.
For 205/55
Sidewall height = 205 × 55%
What profile changes
Higher profile (65–70)
- Softer ride
- Better pothole protection
- More comfort
Lower profile (40–45)
- Sharper steering
- Sportier appearance
- Firmer ride
Low profile tyres often feel harsh on damaged UK roads because there is less rubber cushioning the wheel.
Radial Construction (R)
The letter R stands for radial construction — used on almost all modern vehicles.
Radial tyres:
- Run cooler
- Grip better
- Last longer
Cross-ply tyres are now only used on classics or specialist vehicles.
Wheel Size (Rim Diameter)
The number after R is the wheel size in inches.
R16 = fits a 16-inch wheel
This must match exactly.
A 16-inch tyre will not safely fit a 15-inch or 17-inch wheel.
If you change wheel size, you must also change tyre size accordingly.
Load Index Explained
The number after the rim size shows how much weight the tyre can safely carry.
Example: 91
Higher number = higher load capacity
Important rule
Never fit a tyre with a lower load index than the manufacturer specification.
Equal or higher is safe — lower is unsafe.
Some tyres are marked XL (Extra Load), commonly used on SUVs and heavier cars.
Speed Rating Explained
The final letter shows the tyre’s maximum safe speed capability.
Common ratings:
| Rating | Typical Use |
|---|---|
| T | Standard family cars |
| H | Medium performance |
| V | High performance |
| W/Y | Performance & sports cars |
Even if you never drive that fast, you should not downgrade the speed rating. Vehicle stability systems are tuned for that specification.
Other Markings on Tyres
You may also see:
- M+S – Mud & snow
- 3PMSF snowflake – Winter approved tyre
- Run Flat (RFT) – Can drive short distance after puncture
- Manufacturer marks – BMW, Audi, Mercedes approvals
How Tyre Size Affects Driving Feel
Larger wheels & lower profile
✔ Sharper handling
✔ More grip
✖ Firmer ride
✖ Higher pothole risk
Smaller wheels & higher profile
✔ Comfortable ride
✔ Better on rough roads
✔ Often quieter
✖ Less sporty feel
Keeping the overall rolling diameter close to original is essential to maintain speedometer accuracy and safety systems.
Common Tyre Size Mistakes
Drivers often:
- Mix sizes on the same axle
- Buy lower load rating tyres
- Choose wrong profile
- Fit incorrect rim size
- Prioritise price over safety spec
These can cause uneven wear, handling issues and potential insurance problems.
Why Professional Advice Helps
Reading the sidewall is only part of choosing tyres.
A specialist like GForce Tyres considers:
- Local road conditions
- Driving habits
- Vehicle weight
- Comfort vs performance needs
They ensure tyres are correctly matched, fitted, balanced and inflated — preventing premature wear and safety risks.
Proper fitting also includes balancing and alignment. Learn why this matters on our wheel alignment service page.
Final Checklist Before Buying Tyres
Before purchasing tyres, confirm:
✔ Correct size matches handbook
✔ Load index not lower
✔ Speed rating not lower
✔ Profile suits driving comfort
✔ Wheel diameter matches rim
Understanding tyre sizes means you never have to guess — the sidewall contains all the information you need to choose safely.
If you’re unsure which tyres suit your driving style, you can view our range of cheap tyres in Aldershot to compare budget and premium options.
FAQ – Tyre Size Explained
1. What do tyre size numbers actually mean?
Tyre size numbers describe the tyre’s width, height (profile), wheel diameter, load capacity and speed rating.
For example 205/55 R16 91V shows the tyre width in millimetres, the sidewall height percentage, the wheel size in inches, how much weight it can carry and the maximum safe speed.
2. Can I use a different tyre size than recommended?
You should only use tyre sizes approved by the vehicle manufacturer.
Using the wrong size can affect braking distance, steering accuracy, speedometer readings and may invalidate insurance. A tyre specialist can advise safe alternatives if needed.
3. What happens if the load index is lower than recommended?
A lower load index means the tyre cannot safely carry the vehicle’s weight.
This increases the risk of tyre failure, overheating and blowouts — especially at motorway speeds or when carrying passengers.
4. Does tyre width affect fuel economy?
Yes.
Wider tyres create more rolling resistance which can reduce fuel economy slightly, while narrower tyres usually improve efficiency and wet weather performance.
5. Is a higher speed rating better?
Not always better — but safer.
A higher speed rating improves tyre stability and heat resistance. You should never fit tyres with a lower speed rating than specified for your vehicle.
6. Where can I check my correct tyre size?
You can find it in three places:
- Driver door frame sticker
- Vehicle handbook
- Current tyre sidewall
If unsure, a tyre garage can confirm the correct size before fitting.
