Everything You Need to Know to Keep Your Tyres in Shape

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If you’re flummoxed by the strange jumble of numbers and abbreviations that circle your car’s tyres, as well as amazed by the price variations, this guide will help you to unravel the jargon and keep your wheels in prime shape.

Tyre Width

If you need a replacement tyre, you need to know the size of tyre that you require. This should be noted in your car’s handbook and it can also be found on the existing car tyre. Not all cars have the same tyres front and back, so check them all individually before replacing. The first three digits shown on the tyre refers to its width in millimetres. The most common tyre sold in the UK measures 205mm across the tread from side to side. The fourth and fifth digits reflect the tyre’s aspect ratio or the correlation between the width of the tyre and its height. An aspect ratio of 55, for example, would mean that the tyre’s height amounts to 55% of its width.

Radial Tyres

If your car has an R marked after its aspect ratio, this means it is a radial tyre. In a radial tyre the cord plies within the tyre’s construction are positioned at a 90° angle to the direction the tyre will be travelling in. This serves to make the tyre stronger and more hard-wearing. These days most cars are fitted with radial tyres.

Tyre Diameter

The next two digits written along the rim of the tyre indicate the diameter of the wheel rim that the tyre needs to be fitted to. So, a tyre marked 18 will fit on an 18-inch wheel rim. Strangely, the width of the tyre is measured in metric units - millimetres, but its wheel rim diameter is measured in imperial units, in inches!

Load Index

The figure following the diameter shows the tyre’s load index or the maximum weight it can take. A load index of 75, for example, would be able to hold a maximum load of 387kg. Some tyres are marked to show that they have been reinforced to hold an additional weight, this could be illustrated by REF, REINF, RFD for reinforced of XL or EXL for extra load.

Speed rating

At the end of the tyre code will be a letter that illustrates the tyre’s maximum maintainable speed. A rating of Q, for example, equates to a maximum speed of 99mph.

Tyre Age

After the letters DOT, which stand for Department of Transport, there are eight characters which are the tyre’s serial number and following this are four digits that show which week of which year it was made. So 30/16 would be the thirtieth week of 2016.


Some tyres are designed to be used for a short time in the event of a puncture. The acronyms for this vary from manufacturer to manufacturer, so you will need to check your car’s handbook to clarify this.


Homologation tyres are those that have been developed and approved for a specific vehicle, these are generally associated with high performance sports cars and, again, you will need to consult your car’s handbook for additional information on this.

Why Are There Vast Price Differences in Tyres With the Same Description?

Any tyre can be damaged by a freak nail in the road or similar, but generally speaking, the more expensive brands of tyres should last longer than their budget counterparts, which will likely wear down much more quickly. As the life of a car is best measured in mileage rather than years, however, if you do very little mileage, a cheaper tyre will probably serve you well. If you do a lot of motorway driving and cover several thousands of miles a year, the more expensive tyres, which also tend to offer better grip and fuel efficiency, will be a worthwhile investment.  
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Winter Tyres

As we don’t tend to suffer from prolonged periods of ice and snow in the UK, most new cars sold here are sold with all-weather tyres. These should be adequate to keep you safe on the road, but by switching to winter, or cold weather, tyres in the winter months, you should find your car easier to drive in cold conditions and you may also reduce the likelihood of becoming involved in an accident. Winter tyres are often marked with an MS standing for mud and snow. They offer improved grip, reducing the risk of you skidding on ice or snow; improved traction on the road in wet conditions; and, shorter stopping distances in ice and snow, when compared to standard tyres. In some parts of Europe, winter tyres are compulsory in the winter months, so if you’re planning on driving your car abroad check if you need a tyre change before you go. Winter tyres are not designed for hot, dry days so it’s not advisable to use them year round.
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