Purchasing new tyres: Which information can be found on the tyre sidewall?
Tyre size is provided as width, diameter and height-to-width aspect ratio. The width is a three-digit number measuring the number of millimetres from one sidewall to the other (1). The ratio is a two or three-digit percentage of the height compared to the width (2). The diameter, specified in inches, must match the wheel size of your vehicle.
Tyres can also vary in construction, indicated by the letter R (3). Until the 1970s, cross-ply tyres were the most common; they had a casing made from rubberised cord plies with edges wrapped around the bead wire. In modern car engineering, the radial tyre has completely replaced the cross-ply tyre. The cords in a radial tyre casing run perpendicular to the direction of travel. Viewed from the side, the cords run radially – giving the tyre its name.
The tyres must be able to support the load of the vehicle; this capacity is called the load index. Look up the index to determine the weight, then multiply it by the number of tyres to get the total load supported. The speed rating, denoted as a letter on the sidewall (5), is the maximum speed the tyre is capable of. Be aware that tyres with a higher maximum speed tend to have faster tread wear. The speed rating must be at least as high as the vehicle’s top speed.
The manufacturer also provides you with information on the ideal tyre pressure for optimal operation of the car. Be very careful if operating a tyre near its maximum rated pressure; it changes vehicle handling and increases wear on the tyre.
Be sure to check the sidewall for other information like size (6), safety codes and association icons. They tell you whether it’s approved for your country and meets common quality standards.
What are the requirements for new tyres?
Taken together, the key requirements for a tyre narrow down your selection. But passenger car tyres still come with many other options. Choosing the right tyre for you depends on your driving style and budget.
Are you looking for a quiet, comfortable ride? Tyres in this category have a tyre tread designed to minimise noise. But the tread rubber may be softer, which increases the rate of wear. Therefore, quiet tyres are best suited for paved roads.
Or perhaps you’re looking for tyres that offer the best fuel efficiency? These tyres have a tread with lower rolling resistance, which provides substantially improved fuel economy.
If you drive on unpaved roads or enjoy some off-roading, tyre versatility is essential. An all-terrain tyre may be enough. Or you may consider the added sidewall protection of an off-road tyre. Many specialty 4x4 tyres, such as mud tyres, offer added traction for various terrains.
Finally, be aware that different tyre types handle differently. Give yourself time to adjust when driving, accelerating and braking with new tyres.
Video: Should I buy premium or budget tyres?
Our motoring expert John Smith is testing a set of new premium tyres and a set of budget tyres. He is explaining the differences between both tyre sets. Find out more which set you should choose and why before you are buying insufficient new tyres for your car!