Choosing the Correct Inner Tube Size for Your Bike

If you've noticed markings on your bike tire that read 40-622 or 700 x 38C, you're in the right place. These numbers are crucial for selecting the appropriate inner tube to ensure your ride is safe and efficient. In this article, we'll break down these markings and explain how to choose the correct inner tube size, valve type, and width range for your specific bike.

Understanding the Bike Tire Markings

The numbers and letters on your bike tire serve as a standardized sizing system. This system helps you accurately identify the size of your tire and ensures that you purchase the correct inner tube.

Standard Sizing System

The ETRTO (European Tire and Rim Technical Organization) sizing system is commonly used. In your case, the marking 40-622 refers to the ETRTO size, which is synonymous with 700 x 38C, a standard designation for road bike tires.

Inner Tube Specifications

To ensure a proper fit and function of your inner tube, it's crucial to match the following specifications:

Size

The recommended inner tube size for 700 x 38C is:

Size: 700 x 38C ETRTO: 40-622

Valve Type

Select the correct valve type for your bike. Check your bike's rim to determine whether you have:

Presta valve: Used in high-pressure tires with thin walls. Schrader valve: Used in low-pressure tires with thicker walls and a quick-release disk.

Width Range

Inner tubes are often designed to fit a range of tire widths. Aim for a tube that fits the width range of your tire. For a 38mm wide tire, look for tubes that specify a width range of 35-45mm. This ensures the inner tube is compatible with your tire.

Understanding the Numbers and Their Significance

Now, let's break down the explanations of the numbers you've provided:

40–622

The number 40 refers to the approximate rim width in millimeters, which is standard for this tire type. The 622 indicates the diameter of the bead groove in the rim, which is 622 mm. This is a standard size for 700C tires.

38 mm Width

Your current tire is 38 mm wide. While your rims might accommodate slightly wider or narrower tires, always consider the clearance of the frame to ensure proper fitment.

Wheel Diameter Calculation

The outside diameter of fully inflated 700C tires can be calculated as:

Diameter 2 x Tire Width in mm For a 700 x 38C tire, the calculation would be:

2 x 38 mm 76 mm 622 mm 76 mm 698 mm (approximate outside diameter)

However, the exact diameter isn't as important as the rim diameter, which is 622 mm.

Conclusion

In summary, if you're replacing a tire marked as 40-622 or 700 x 38C, you should choose an inner tube that is compatible with these dimensions. Ensure you match the valve type, and consider the width range of the tire to avoid any size-related issues.

By selecting the correct inner tube size, you'll enhance your riding experience and maintain the safety and performance of your bike.