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We’re getting to that time of year when I’m sure I’ll have plenty of reports relating to tyres but before we get into the summer/winter tyre debates a question has come up regarding speed ratings on tyres. When a car is new tyres are often fitted by the manufacturer that have a speed rating much higher than the car is capable of travelling. For example a car may be fitted with V rated tyres, safe to a speed of 149 miles per hour. The question is should the same tyres be fitted when they are due Read more »

Recent discussions regarding the use of winter tyres in the UK following our harsh winter has spurred on many to provide more advice suggesting that winter tyres may not be necessary if drivers simply treated tyres with a little more respect. Simple maintenance such as the regular checking of pressures would be a start. The National Tyre Distributors Association have followed up with the following points when replacing tyres:

• Tyre size markings across an axle must be identical.
•  Tyre construction across an axle must be the same
• The load index must be equal or be higher than the manufacturer approved tyre for the vehicle
• It is recommended that the speed rating is either equal or greater than the original approved tyre.
• Mud and snow – winter tyres should ideally be fitted in complete sets and should not be mixed with other tyre types across an axle.
• It is recommended that when fitting two new tyres, they are fitted to the rear axle unless rear tyres are a different size to the fronts or the vehicle manufacturer’s handbook states otherwise.
• There may be special dimensional requirements preventing the mixing of tyres such as 4WD vehicles. 

I know I have provided this information before but do you know what the markings mean on a tyre? Lets take a tyre that reads 195/65 R 15 91 H. Here’s what the markings mean: 

195 : The width of the tyre in mm, also called the section width.
65 : The aspect ratio is the ratio between the sidewall height (side of the tyre) and the width of the tyre. It is expressed as a percentage.
R : The type of construction (R for radial).
15 : The internal diameter of the rim in inches.
91 : A tyre’s load rating is identified by a number and corresponds to the maximum load the tyre can withstand at maximum pressure.
H : Speed rating (also known as Performance Index). Indicates the maximum speed at which the tyre can bear a load corresponding to its load rating 

For more information on the tyre markings visit any of the major tyre fitter websites. By Graham Hill

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