Let's say you spend some time riding a bike, on snow, in Alaska, in February.
Let's assume that the snow conditions are, for Alaska, average. You leave your starting point and the whole bike is shiny and clean. Most of the bike will stay that way, except for the wheels. After a few hours, your rear rim starts to collect snow. A little at first, then progressively more. Lots of factors affect how soon and how much, but pretty soon it starts to look like this:
At first blush you don't worry too much about it. It's just snow, it isn't hurting anything. But snow weighs something, and the more that packs in there the more weight you're pushing around and around and around.
After a few days you can end up with a pretty significant amount frozen to the rim.
I've always just stuck my hand in there and scraped it out when I started to notice the mass. But I've also always thought to myself that there had to be a better way.
I don't know that I've found that 'better way' just yet, but I've started down the road...
I started with a Zipp disc blank. Used a sawzall to get the cut started through the carbon, then finished it by hand.
After too many hours of cutting, grinding, dremeling, sizing, cutting, resizing, and then some caulking:
Curing now, should be ready to ride in the AM.
I'll do a brief fully loaded ride to triple check, well, everything, and then it all gets boxed tomorrow PM and sent north.
How's that for geekery? My only regret is that I didn't start on it sooner. Never enough time, and my black caulk skills could have used some polishing...