Trying to read tyre sizes can be a nightmare. So many different standards and ways of writing sizes exist, with variations in what numbers are shown, what format they are shown in and even whether the units are imperial (inches) or metric (millimetres).
This article will give you a quick and easy rundown of some of the main ways tyre sizes are written down, so that next time you need a tyre, you won’t have to agonise over which tyre will fit your bike.
Classic Style
outer diameter x width
e.g. 16 x 3.0
Often found on normal bicycle tyres. This is usually measured in inches. The first number is the outer diameter of the tyre and the second number is the tyre width. Sometimes the tyre height is also included, and the size is written as diameter x height x width (e.g. 28 x 1 5/8 x 1 3/8).
Typically, inch-based measurements are not precise or accurate and really are just approximations – you can expect some variance between tyres with the same measurements. For example, 622 mm and 635 mm tyres are both classified as 28-inch.
French Size Markings
e.g. 700 x 35C
Similar to the classic style, except measured in millimetres. The first number is the outer diameter, followed by the width, then a letter at the end indicating the inner diameter (or rim diameter). In this case, C is 622mm.
ISO Standard
width-inner diameter
e.g. 37-622
A European standard introduced to fix inconsistencies in tyre size labelling and replace older systems. Measured in millimetres. The first number is the width of the tyre, and the second number is the inner diameter (or rim diameter).
Scooter Tyres
width-inner diameter or height/width-inner diameter
e.g. 3.00-10 or 3.00/3.50-10
Similar to the ISO standard, except measured in inches. If the height and width are the same, only the width is included. If they are different, then first the height is given, then the width, then the inner diameter.
Motorcycle Tyre Style
width/ratio-inner diameter
e.g. 130/60-13
We included this strange measurement system because some scooter tyres use it. There is a mix of metric and imperial units being used. The first number is the width of the tyre in millimetres, followed by the aspect ratio of the tyre, then the inner diameter.
The aspect ratio of the tyre is the ratio of the height of the tyre to the width written as a percentage. In the example, the height is 60% of the width of the tyre, making it 78mm.
Tyres are being made and used all over the world, meaning there are likely many more standards we have not included. In addition, not all manufacturing companies necessarily adhere exactly to the standards we described. While we have tried to show you the most common ones for electric bicycles, tricycles, scooters and mobility scooters, there may be some we missed or some tyres that don’t follow the standards. Next time you end up in the market for a new set of tyres, hopefully you can refer back to this article to help you know what to look for!