How to understand your tyre size, speed rating and more

Written by Summit Tyres April 2019

 

Have you ever taken a good look at your tyres and noticed number and letters that you don’t quite understand? Well, if you haven’t, you should, because this combination of letters and number tells you everything you need to know about your tyres.

These markings define unique elements of your tyres such as the speed rating, load rating, rim diameter and width. By taking note of our simple diagrams and tables below, you will be able to understand your tyres in no time.

To begin with, the diagram below shows a tyre size; a combination of numbers and letters: 205 55 R16 91W

 

A diagram to highlight tyre size markings

 

In order to understand exactly what this means, please see below:

A. TYRE WIDTH

The width of the tyre in millimetres.

B. ASPECT RATIO

A percentage of the tyre width, or otherwise known as the profile height.

C. WHEEL DIAMETER

The tyre’s inner rim diameter in inches.

D. LOAD INDEX

The Load Rating of the tyre

E. SPEED RATING

The Speed Rating which indicates the tyre’s maximum speed at full load

 

But it does not stop there. Another combination of letters and numbers represents different aspects of your tyres that you may want to take into consideration. These will tell you the date of manufacture, whether your tyres are run flat tyres, if your car tyres have been reinforced and which car manufacturer your tyres are best suited with.

You can read more about these tyre elements, as well as others, by clicking the text below.

Understanding your tyre size
How to read your tyre speed rating
What is your tyre load rating?
What is my tyre's manufacture date?
My tyres say they are 'reinforced', what does this mean?
Are my tyres run flat Tyres?
What does homologation mean?

 

Understanding your tyre size

It depends completely on your car and wheels as to what your tyre size is, but your tyre size will always be present on your wheels as a sequence of numbers and one letter that is 8 digits long. This can look like this: 205 55 R16. Check our table above to see the meanings of each element of your tyre size.

Before you decide to change your car tyres, it is essential to understand them. Check the current tyre size and also your vehicle handbook to ensure they are the correct ones. If you misunderstand your car tyres and buy the wrong ones, they may not fit at all or be appropriate for your car.

 

How to read your tyre speed rating

It is important to understand the absolute maximum speed that your car can physically perform. Although the law decides how fast your car can go on the roads, the speed rating informs you of the ultimate speed your car can reach. This is presented by a letter at the end of the tyre size combination on your tyres.

See the table below for more information on Speed Rating:

Speed Rating

Maximum Speed

Q

99mph

R

106mph

S

112mph

T

118mph

H

131mph

V

149mph

W

168mph

Y

186mph

 

What is your tyre load rating?

Your tyre’s load rating informs you how much weight your car can hold safely. Whether you’re heading on holiday or moving to a new house, there always comes a time when your car is full to the brim with people and possessions. But do you ever think about the maximum load capacity your car is capable of carrying?

This is when your tyre load rating can come into play. The tyre load rating highlights the absolute maximum weight each tyre is able to carry. It is essential to understand your tyre load rating as, if you over exceed this rating, you could be in for an unsafe and uncomfortable drive, invalidate your insurance or even damage your tyres.

See the below table for the weight capacity in kg of each possible load rating:

Load Index

Load in kg

62

265

63

272

64

280

65

290

66

300

67

307

68

315

69

325

70

335

71

345

72

355

73

365

74

375

75

387

76

400

77

412

78

425

79

437

80

450

81

462

82

475

83

487

84

500

85

515

86

530

87

545

88

560

89

580

90

600

91

615

92

630

93

650

94

670

95

690

100

710

101

825

102

850

103

875

104

900

105

925

 

A diagram to show tyre information

 

What is your tyre's manufacture date?

Your tyre’s manufacture date tells you when and where your tyres were manufactured. This date comes after the words DOT on your tyres. These letters stand for ‘Department of Transport’ which means that the applicable tyre meets the Department of Transport safety standards.

After DOT, there are characters that are only applicable to individual manufacturers. If there was ever a problem with your tyre, these characters would help identify exactly which tyre yours is and the exact production facility it was produced in.

The last four numbers after the manufacturer code represent the week and year of which the tyre was produced. To give an example, 1218 shows that the tyre was created in the 12th week of 2018.

 

Reinforced tyres: what does this mean?

The word ‘Reinforced’ on your car tyres means that your car tyres have been reinforced to handle their maximum capacity load.

If you cannot see the word ‘Reinforced’ printed on the sidewall, you may see a two to five long letter combination. These letter combinations are outlined below for their definition. They either mean your car tyres can handle an extra load or they have been reinforced.

‘Reinforced’ Combination

Definition

XL

Extra Load

EXL

Extra Load

RF

Reinforced

REINF

Reinforced

RFD

Reinforced

 

Are my tyres run flat tyres?

If your tyres are run flat tyres you will see a small combination of letters displayed after the date of manufacture. These letters have different definitions and are applicable to certain manufacturers.

If you have your tyres state that they are run flat, this simply means they have been specially produced with a strengthened sidewall. A strengthened sidewall can help hold the weight of your tyres become punctured or lose air pressure.

Below is a table that represents the different kinds of run flat tyre combinations you may see on your tyres:

Letter Combination

Definition

Manufacturer

RFT

Run Flat Technology

Pirelli, Firestone, Bridgestone

EMT

Extended Mobility Technology

Goodyear

ROF

RunOnFlat

Goodyear

DSST

Dunlop Self Supporting Technology

Dunlop

SSR

Self-Supporting Run Flat

Continental

MOE

Michelin Run Flat

Michelin

ZP

Zero Pressure

Michelin

 

What does homologation mean?

A homologation is a combination of digits that show if your tyres were specifically designed for a particular car manufacturer.

Most vehicle brands and manufacturers that you know will have their own symbol or letter combinations to show that they have received an OE status and met the tyre manufacturer’s safety standards.

Refer to the table below for more information regarding particular manufacturer’s homologation symbols:

Homologation Symbol

Manufacturer

A0

Audi

R0

Audi Quattro and S variants

A

Toyota Auris

G

Volkswagen Golf

VO

Volkswagen Touareg

LRO

Land Rover

FO

Ford

MO

Mercedes

MO1

Mercedes AMG

J

Jaguar

N0, N1, N2, N3, N4, N5, N6

Porsche

AR, AZ

Alfa Romeo

MOE

Mercedes Run Flat

BMW and Mini

 

For everything you need to know about your tyres, visit our help and advice page.

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