Determining Bike Tire Size Made Easy

On the sidewall of your bike tire, you will find several numbers that may seem confusing at first. These are different sizes that refer to the diameter and width of your bike tire. Here is an overview of how to read bike tire sizes:

• ETRTO size: This system is an international size standard in millimeters. The first digit is the tire width, the second three-digit number is the tire inner diameter in mm. It is the most accurate way to match tire and wheel size, and is therefore included in the data sheet for all tires in our online shop.
• Inch size: This size system is often used for mountain bikes. The first number stands for the approximate outer diameter of the tire in inches, the second for the width. In particular, the width of a tire depends heavily on the rim used.
• French size: The oldest bike tire dimensions system, found on road and gravel bikes. The first number stands for the approximate outer tire diameter in millimeters, the second for the tire width in millimeters. The final letter was originally intended to give an indication of the recommended rim width, but is no longer reliable.

Here we show you how different the sizes printed on the tires of your bike can look and what they mean, using the example of MTB, gravel and road bike tires:

Our expert tip: For easy comparison and reliable compatibility, you can find the ETRTO information on the data sheet of every bike tire in our online shop.

Would you like to switch to a wider or narrower bicycle tire? To find out whether tires and rims fit together, you need to consider the size of your rim as well as the tire size. The ETRTO specifications are also used here. You can find it on every data sheet in our online shop. It specifies the inner dimension (rim width) and the rim diameter in millimeters. The ETRTO specification 21-622 therefore describes a 28-inch rim with a diameter of 622 mm and an inner rim dimension of 21 mm.

Different tire widths are possible depending on the width of your rim. In order to find the optimal tire-rim combination for you, you should first consider your riding style, the air pressure and the terrain you are riding on. The rougher the terrain, for example, the more flexible a tire needs to be to absorb bumps and adapt to the surface. As it can only do this optimally with sufficient volume and low air pressure at the same time, a wide rim support is necessary. We also recommend checking compatibility with your bike if you want to switch to wider tires. Some frames and forks only offer limited tire clearance. Finally, we recommend that you follow the rim and tire manufacturer's specifications. Leading manufacturers such as Continental, Schwalbe, Maxxis, DT Swiss and Mavic have corresponding lists with compatible tire-rim combinations or tire width recommendations in mm.

1. Check ETRTO sizes on bicycle tires and rims
2. Consider riding style, air pressure and terrain
3. Check the compatibility of the frame and the recommended tire width of the bike manufacturer
4. Observe the rim and tire manufacturer's specifications

Our expert tip: If you ride hookless rims, you should only combine them with tubeless ready bike tires.