Holes in side of carbon rims - why?

[oldguy00]

Hi all,

I've noticed with many carbon wheels, you sometimes have a small hole drilled in the side of the rims.
A friend recently got a couple sets from Flo, and one set had one hole in each rim, the other set had one on the rear wheel but not front.

What is up with these? I would think maybe drain hole, but why the inconsistency?

[Mark McM]

Some types of construction are more prone to collecting water in the rim than others. For example, on Flo's carbon/aluminum rims, the spokes pass through large holes in the carbon fairing before reaching the nipples in the aluminum extrusion. These pass-through holes in the carbon can let in a lot of water, so the these rims typically have drain holes. On other rims, the nipples fit tightly in the rim holes, largely preventing water from entering.