How to calculate what tyre size you need

Most drivers know that not all tyres are the same and that the likelihood of a random tyre fitting your vehicle is fairly minimal. Tyres are manufactured with characteristics to suit driving in different conditions, from wet and icy to Formula 1.

The type of tyres on your car will have a direct effect on its safety, how it handles in the wet, cornering, general handling and - of course - braking. Tyres can also have a big effect on the comfort of driving your car; however, before you get to any of those factors, the tyres need to be the correct size. You could have the best tyres in the world, but they are worthless if they are too big or too small for the wheels of your vehicle.
Even the most careful driver needs to replace their tyres from time to time. The state of your tyres will be assessed during your car’s annual MOT; if there are bald patches or shallow tread, you will need new tyres. Protyre offers MOTs that deliver terrific value; in addition, as tyre specialists, our knowledgeable staff can help you immediately with replacement tyres to get you back on the road.
You can also upgrade your tyres for greater comfort and safety. Before you can shop for tyres, you will need to know what size is suitable. The first point of reference should be your car manual. This should have information on the tyres you already have, which will be labelled with measurements regarding the diameter of the wheel’s rim and the maximum load recommended. If the manual is lost, you can bring the car to a Protyre garage and our friendly staff will advise you.
The diameter is a critical factor. This is related to how far the tyre will travel during a revolution, which affects gearing, torque, traction and the speedometer. A tyre is sized by its inside diameter. The outside diameter is used to measure the aspect height or tyre profile, which is dictated by the sidewall. It gives the width of the tyre against its height as a percentage. In general, a tyre that has a low profile, or short sidewalls to their width, will give a firm ride and good handling; however, these tyres can cost more and be noisier than tyres with higher aspect ratios. Change one of these measurements in a tyre and it will have an impact on the others. The diameter should remain constant.
All Protyre garages have staff with many years’ experience who can help you with all the decisions regarding tyres. Go online for easy shopping at the Protyre website, where you will find a vast selection of tyres from all the major manufacturers in a range of sizes, prices and features. We also have lots of great deals, and our prices include tyre fitting - sometimes on the same day. If you are not sure what kind of tyres suit your car, call us and book a free assessment.

Protyre runs more than 100 garages in its extensive network, so there is sure to be a Protyre garage near your home or your place of work. To find your local Protyre garage, click the button below:

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About the author

David Sholicar

David is the National Retail Operations Manager for Protyre. One of David’s areas of responsibility and ...

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