It takes a special spoon-shaped hammer that is driven between the tire bead and the rim, all the way around. Once the tire is loose on both sides of the rim, the bead ring is pushed down toward the center of the rim, and the lock ring is pried off. Lift the bead ring off, flip the rim over, and support it on something lilke an old brake drum. A few taps of the hammer should drop the tire off the rim. Sometimes a good squirt of WD-40 helps the tire break loose if the rim and tire have rusted together. Quite often, a badly-rusted rim is a real PITA to disassemble, and it's also likely that one with a heavy rust buildup will also be damaged too badly to reassemble safely.
Jerry

Edit: Here's a couple of pics:

http://www.gemplers.com/product/6A/32-Duckbill-Bead-Breaking-Hammer

http://www.gemplers.com/product/T11D/17-Short-handled-Bead-Breaking-Hammer

The long-handled hammer is better for a pro tire shop. The shorty costs less, and is OK for occasional tire work.
Jerry


Last edited by Hotrod Lincoln; 08/09/2008 2:17 AM.
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