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:

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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.

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:

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

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.

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© 1999-2013 by Delticom / mytyres.co.uk 25.05.2013 15:25