Dude, did you read this entire thread? "A little rain" will not cause the problems that the OP experienced with his rims. It's impossible to say exactly what did cause it, but "a little rain" is certainly not the cause. If I had to bet, he either ran through a chemical that caused the etching or a combination of brake dust suspended in chemicals / rain that were allowed to dry on the surface and cause the etching. Brake dust is a killer on any surface let alone bare aluminum. The bottom line is that polished aluminum wheels require more upkeep than coated wheels because they are basically unprotected metal surfaces.
Brake pads are made from a few different components, including monofilament carbon fibers, metal filings, Kevlar fibers and polymer adhesives. Most of the time its the actual adhesives that cause your etching and staining. When the brake pad adhesivs become wet they turn into an acidic chemical that can etch the surface of the rim. What your actually seeing with this etching is re-polymerized and flocculating brake pad adhesive that adheres to the surface (look up flocculate if you don't know what it means).
The only way to stop the etching is to use wax or sealant to act as a sacrificial surface (just like you do on the surface of your car). The dust will eat at the wax instead of the surface of the wheel. However, if you leave it on there too long, it will eventually get through the wax surface and hit the wheel surface. That's where your cleaning habbits take over and obviously a surface like polished aluminum (which is once again a raw metal surface) becomes much more suseptable to etching than a surface that has a painted, chrome or powder coated barrier on its surface.
oke:
