We will use the example 205/55 R16 91V, a common size for family hatchbacks and saloons. Look at the sidewall of your own tyre as you read.
205: the section width
The first number is the width of the tyre in millimetres, measured from sidewall to sidewall. A 205 tyre is about 205mm wide. A wider tyre puts more rubber on the road, which can add grip but may also affect fuel economy and noise.
55: the aspect ratio
The second number is the height of the sidewall as a percentage of the width. In our example the sidewall is 55 per cent of 205mm, around 113mm. A lower number means a shorter, stiffer sidewall, common on sporty cars; a higher number gives a softer ride with a taller sidewall. This is why low-profile tyres are more prone to pothole damage; see tyre bulge in the sidewall.
R: the construction
The R stands for radial, the construction used on virtually all modern car tyres. You may see other letters on older or specialist tyres but radial is the standard.
16: the rim diameter
The number after R is the diameter of the wheel rim in inches. This tyre fits a 16-inch wheel. The tyre must match the wheel, so you cannot fit a 16-inch tyre to a 17-inch rim.
91: the load index
The two- or three-digit number is the load index, which refers to the maximum weight each tyre can carry. It is a code rather than a weight, so 91 equates to a specific load figure in a standard table. See load index explained. You should never fit a tyre with a lower load index than the vehicle maker specifies.
V: the speed rating
The letter is the speed rating, the maximum speed at which the tyre can carry its rated load. See speed ratings explained. Like the load index, you should not go below the vehicle's required rating.
Other markings you may see
- C after the rim size indicates a commercial tyre, as on vans; see van tyres.
- XL or Reinforced shows an extra load tyre.
- M+S or the three-peak mountain snowflake symbol marks tyres built for mud and snow or severe winter use; see winter vs all-season tyres.
- RFT or Run Flat indicates a run-flat tyre; see run-flat tyre puncture.
- DOT followed by characters includes the date code; see DOT code guide.
Where to find the right size for your car
The size recommended by the maker is in the handbook, often on a label inside the driver's door frame or fuel flap. Do not assume the tyres on your car now are correct: a previous owner may have fitted something else. Where a car was sold with several wheel options, check the wheel size too.
Why the size matters
Fitting the wrong size can affect speedometer accuracy, handling, braking and ABS or stability control operation. It may also cause rubbing on the bodywork or suspension and cause an MOT or insurance problem. If you are unsure, ask a technician.
Getting the right tyre fitted
When you call TyreBlitz, read out the full size, load index and speed rating, as well as the vehicle registration. Our technicians can then bring the correct tyre. See mobile tyre fitting and emergency tyre fitting. We work across areas including London, Manchester, Birmingham and Leeds; see the areas list. Call now for a quote on 0800 772 0355 or book now.
A quick worked checklist
- Find the sidewall markings on the tyre you want to replace.
- Write down width, aspect ratio, rim size, load index and speed rating.
- Check them against the handbook.
- Note whether the tyre is a run-flat, XL, directional or commercial type.
- Check the age using the DOT code.
Common mistakes
Reading the DOT code number as the size, forgetting the load index and speed rating, ordering a tyre for the wrong wheel diameter, or assuming all four tyres on the car are the same size. Some cars, especially performance models, use different sizes at the front and rear.
Frequently Asked Questions
What does 205/55 R16 mean?
205mm width, sidewall height 55 per cent of the width, radial construction, 16-inch rim.
Can I fit a different size tyre?
Only within the sizes approved for your vehicle. Check the handbook or ask a fitter.
Where is the size on the tyre?
Moulded into the sidewall.
Can you help me work out my size?
Yes. Call now for a quote on 0800 772 0355.
Related Help
Need help with your tyres now?
Call now for a quote, or book now online. Phone 0800 772 0355.