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Identifying the size of tyres on your car

Sidewall Markings

On the sidewall of a tyre you will find various codes and markings. Amongst these you will find the size.

Tyre Sizes

Tyre sizes are made up of a number of different numbers and letters. For example tyre size 185/60 R 14 82 H is made up of the following information:

185 The tyre section width in millimetres
60 The aspect ratio in % (the height of the sidewall divided by the tyre's width)
R Denotes the tyre's construction type - in this case it's a radial
14 Rim diameter in inches
82 Load Index
H Speed Rating

This is all the information you need to order your tyres if you would like to know more read on

Aspect Ratio

Aspect ratio is the ratio of a tyre's width to it's height. A 60 series tyre, therefore, is a tyre whose height is equal to 60% of its width.

Speed Ratings

All tyres carry a speed symbol in the form of a letter indicating the maximum speed for which the tyre is intended. The table below shows which speed goes with each letter.

Speed symbol Maximum speed km/h
mph
N 140 87
P 150 93
Q 160 99
R 170 106
S 180 112
T 190 118
H 210 130
V 240 149
W 270 168
Y 300 186
ZR 240 149
Load Indices

The load-index figure imprinted on the sidewall of the tyre denotes the maximum load capacity of a tyre when driven at maximum speed. A list of load indices and maximum weights is give below:

Li kg Li kg
65 290 94 670
66 300 95 690
67 307 96 710
68 315 97 730
69 325 98 750
70 335 99 775
71 345 100 800
72 355 101 825
73 365 102 850
74 375 103 875
75 387 104 900
76 400 105 925
77 412 106 950
78 425 107 975
79 237 108 1000
80 450 110 1030
81 462 110 1060
82 475 111 1100
83 487 112 1120
84 500 113 1150
85 515 114 1180
86 530 115 1215
87 545 116 1250
88 560 117 1285
89 580 118 1320
90 600 119 1360
91 615
 
92 630
 
93 650

Tyre Age

Tyres carry a three digit age code on the sidewall indicating the month and year of manufacture. For example 129 means the tyre was manufactured in December 1999.

Other Markings

M+S - Identifies Mud and Snow tyres

DOT Codes - Coding satisfying the requirements of the US Department of Transportation contain a mixture of letters and numbers such as DOT DVDE MTA 129

E-Marks - Tyres for sale in the European Community must carry an E -Mark in accordance with ECE Reg 30 - eg E4 027550

Air Pressure

The main function of a tyre is to carry the load of the car. Therefore, it is vital that correct air pressure is maintained. Over-inflation will cause rapid and irregular wear.
Under-inflation will damage the tyre structure leading to possible accidents.
Improper air pressure will not allow the tyre to function within its design. For best performance maintain the air pressure recommended by the vehicle manufacturer and/or the tyre manufacturer.

Wheel Alignment and Balancing
A major cause of rapid tread wear is improper wheel alignment and balancing. Abnormal noise, vibration and harshness of steering is a signal that alignment and balancing may be improper.
And finally, The Law
  1. Tyres on cars, light vans (not exceeding gross weight) and light trailers must have a tread depth of at least 1.6mm across the central three-quarters of the breadth and in a continuous band around the entire circumference of the tyre.
  2. Tyres must be suitable (ie of the correct specification and size) for the use to which the vehicle is being put and must be inflated to the manufacturers' recommended pressures.
  3. Tyres of different types must not be fitted to opposite wheels of the vehicle (for example, radial-ply tyres must not be fitted to a wheel on the same axle as wheels already fitted with cross-ply tyres and vice versa, and a two-axle vehicle must not have radial ply tyres on the front axle if cross ply tyres are fitted to the rear axle)
  4. No tyre must have a break in its fabric or a cut deep enough to reach the body cords. No cut must be more than 25mm or 10% of the tye's section width in length, whichever is greater.
  5. There must be no lump, bulge or tear caused by separation or partial fracture of its structure, neither must any portion of the ply or cord structure be exposed.

© 1999-2014 by Delticom / mytyres.co.uk 22.10.2014 09:28