If the crack is a ring around the rim where the brake pads grip, You have thinned the sidewall of the rim down..
your miles of stopping have added up.
buy another rim and have the wheel rebuilt.. get a welded seam machined rim this time.
A BMX Aluminum rim .. if the new rim needs a different spoke length, so Be It.
In the future Remove any grit embedded in the brake pads..
No, You should not look for a " high quality BMX steel rim" that is an oxymoron,
as the steel stuff is relegated to the cheapest end of the coaster brake kid's bike market.
If you have the front wheel rebuilt around a Drum Brake Hub, then there will no longer be a friction between brake shoe and pad stopping the bike,
and wearing down the rim sidewall..
Last edited by fietsbob; 09-13-10 at 10:10 AM.