Rolling circumference on tyres: What is permitted?

The rolling circumference is the exact distance your tyres will travel in one revolution – and therefore a critical parameter for working out the tyre dimensions. All the more important, then, for you to be able to calculate the tyre size!

Calculating the tyre size: For new tyre sizes, this is essential

Swapping tyres isn't a problem for most drivers. At least, not if the old and new tyre sizes are the same. However, that is not always the case. Why? The reasons can vary enormously and relate mostly to the driver. For example, perhaps you want to save fuel by using a smaller tyre size. Or, you want a larger tyre size to stand out on the roads. However, the reason is often much more mundane. For example, when you buy a new car and wonder if it can use your old tyres. Whatever it is you have in mind, these examples all have one thing in common: a new tyre size also means that the rolling circumference changes. Unintended consequences cannot be ruled out. The reason is that if the rolling circumference differs too much from the standard tyres, it can lead to problems at MOT inspections. So, what is permitted?
This question cannot be answered the same way for everyone. Ultimately, tyre sizes differ from car to car. To find out the tyre size for your car, often all you have to do is look at the sidewall of your tyres. This information is also provided on the inside of the driver’s door. If not, it will be entered by the technical inspector in your car documents. However, these details do not tell you the actual tyre size of your car tyres. However, you can also work it out using this formula.

Uniroyal. A brand of Continental.