Explained: tyre sizes

Explained: tyre sizes

When looking at car valuation, don’t forget that even a guide price needs to be compared with what the car in front of you is actually like. For instance, a car can be perfectly fine in every respect, but might still have tyres that need replacing. And tyres can be expensive.

Our guide to tyre sizes will help you understand what all the letters and numbers written on those sidewalls actually mean – and how that has an impact on cost. It will also help you make sure you get the right tyres for your car, should they need replacing.

Why are tyre sizes important?

Having the correct size of tyre for your car will mean that it works as the manufacturer intended. Or, put it another way: if you fit the wrong tyre size it will affect the car’s gearing (making it faster or slower, compared with the speedometer) and the amount of grip it is supposed to have.

Having the right load and speed rating for your vehicle is also important.

How do I find out what size tyres my car needs?

If you’re buying a used car, it’s probably best not to rely on the tyres currently fitted. Instead, see if you can find the tyre sizes in the owner’s manual.

If there’s no manual in the car, the websites of many tyre sellers – such as Kwik Fit or Black Circles – will allow you to look up the correct tyre size using your number plate.

What do the letters and numbers on the side of a tyre actually mean?

Modern tyre sizing always follows the same format. Let’s take a tyre marked as a 195/55 R16 87V as an example.

The first group of numbers – 195 – represents the tyre’s width in millimetres. The higher the number, the wider the tyre. Wide tyres are associated with high grip, but they can also unnecessarily reduce fuel efficiency if your car doesn’t need wide tyres.

The second group of numbers – 55 – represents the tyre’s sidewall height: the amount of tyre between the wheel and the top of the tyre. However, just to be confusing, this is a percentage of the width (55% in this instance), rather than a measure in millimetres. Because of this, if you do go for different widths of tyres, you have to be careful to make sure the sidewall height stays correct.

Carrying on, the R16 combo tells us this is a radial tyre designed for a 16-inch wheel. Yep. While the width is in millimetres, the wheel size is in inches. More straightforwardly, all modern cars use radial tyres, the most up-to-date form of tyre construction; classic cars may have originally come on cross-ply tyres, which are typically less grippy.

The final 87V element refers to the load rating and the speed rating. In this instance, 87 is 615kg, while V represents 149mph. The higher the number the greater the load, and the later in the alphabet the faster the speed rating.

So, while tyre sizing might look complicated, it is in fact quite clear and logical – once you know how to decode it, the information is available to anyone who cares to look.