How to Properly Drill Drain Holes in Carbon Fiber Bicycle Rims: A Comprehensive Guide

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What are Drain Holes?

These holes are designed to allow accumulated water inside the rim to drain out. They are a practical feature that enhances the performance and longevity of the rim, especially in challenging riding environments.

These Two holes serve multiple purposes:

Water Drainage: They enable water that has collected inside the rim's edge to escape. This is particularly beneficial in wet conditions or when water enters the rim during cleaning.

Ventilation: Drain holes help in ventilating the inside of the rim, preventing the buildup of moisture and potential issues such as mold growth or rim corrosion.

Weight Reduction: Drain holes also contribute to reducing the overall weight of the rim, although the effect is typically minimal.

Before proceeding, make sure you understand the implications. It's a general guide

  • Prepare the necessary tools: You will need a drill with a small drill bit (2.5 millimeters), masking tape, a marker pen, and a piece of cloth.

  • Prepare the rim: Clean the area where you intend to drill the hole, removing any dirt or debris. Use masking tape to mark the exact location of the hole.

  • Positioning of Drain Holes: We recommend drilling one hole on each side of the carbon rim (two holes in total per rim). These holes should be drilled at a 90-degree angle to the valve stem. The position of the drain holes should be 14mm from the edge of the rim, with one hole on the drive side and the other on the non-drive side. This positioning allows water to be easily drained out.

    Video of Drilling Drainage Holes in Wheel Rim

  • Drilling: Carefully drill through the edge at the marked points. Use a slow and steady speed to prevent the drill bit from slipping or causing damage.

  • Cleaning: After drilling, use a cloth to wipe away any remaining carbon dust from the hole and surrounding area.

  • Test ride: Before riding, ensure the rim is securely mounted on the wheel and that the holes do not compromise the structural integrity of the rim.

It's important to note that drilling holes in the rim is a modification that should be approached with caution. Before proceeding, make sure you understand the implications, and if necessary, consult with BTLOS for guidance.


Do the drain holes affect tubeless sealing?

No, the drain holes typically do not affect tubeless sealing. These holes are strategically placed in areas where they do not interfere with the sealing properties of the tire and rim interface. As long as the tubeless setup is properly installed and sealed, the presence of drain holes should not compromise the effectiveness of the tubeless system.

Will drilling the holes myself void the warranty?

Drilling holes should not damage the rim if done correctly. However, if you have concerns, it is recommended to request BTLOS to drill the drain holes when ordering to avoid any warranty issues.

At BTLOS, the drain holes are not necessary, while the 2.5mm holes help reduce the amount of water that may accumulate inside the rim during riding, preventing water buildup inside the rim. If you need drain holes, you can choose them when placing your order. At BTLOS, the sidewalls of the drain holes are reinforced. It is recommended that riders in wet areas order rims with drain holes. If you want to drill the holes yourself, please refer to the video guide above.