Drain hole -Why is there a hole in new carbon rim? Apr 15, 2022

“Who cares, tiny holes are there and they serve a purpose!”

That’s true. Even though, does it really necessary to have water drain hole on the side of carbon bike rims?

Even as tight as the spokes you can, the water can still get inside through spoke holes as well as valve hole. After bike cleaning, riding in rain, or crossing flooded terrain, the water greatly possibly goes into rims, and maintains for many weeks and even months if not properly deal with.

The accumulated water inside a hollow rim add weight, which makes bad effects, such as bike imbalance, noisy and poor control to the bike. Another critical problem is that the water will corrode metals including steel spokes, aluminum alloy nipples and brass nipples.

Drain holes provide an exit for accumulated water inside rim during rolling or stationary by gravity and centrifugal forces.

ProX drill 1 pc of drain hole on each side of carbon road rim

In ProX, we drill 1 hole in each pc of carbon road rims (total 2 holes on each rim). The holes are drilled 90° to the valve hole. They are tiny holes with only 2.5mm diameter on the chamber between the section of spoke holes and rim bed. It is 14mm away from rim edge. One hole is on the drive side and the other is on non-drive side.Let water out as easy as possible!

Another function of such tiny hole is some kind of pressure relief, especially for tubeless tire using by high pressure shock pump.Maybe stupid question but do you install tubeless tape/valve properly? If not, the abundant high pressure will leak from tire bed and get into the “stomach” of carbon rims. If the volume of leak air is too much while inflation continues, it may lead to blasting of carbon rim! Though the chance is not high, it is a nightmare if happened. Thus, more and more brands tend to drill such water drain hole.

ProX has added such drain hole on all our carbon road rims. ProX team focus on carbon rims and carbon wheels, keep improving our products for better riding experience.

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