http://www.afrigadget.com/2010/02/09/rim-stoves-mamaput-street-food/
In Africa, these are permanent, with rebar welded to a tire rim to keep it off the ground for air flow underneath, but three or four bricks would do the same trick if you've got the rim and are in an emergency situation. It's a nice starting point for innovation in a disaster.

The street vendors shown use charcoal, which would be nice, but I'm confident I could burn wood scraps to the same effect (although the heat would be less even than charcoal - c'est la vie). If I had green wood, I could get some nice coals going.

Geez

Almost every provincial campground around here has these in the camp sites. Usually made from bigger rims, but the same Idea.

If you have a few bricks you can make a rocket type stove as well. The key seems to be getting air to the bottom of the fire.

Have one down on the farm that we use for our camp fire. A big coal truck rim, just sit it on top of rocks and toss wood in the center.

The key to a wood gasifier stove is heating the air. Heated air passes over uncombusted material (heating and drying it, releasing combustible gases) before the air+combustible gases mixture is sucked into the base of the fire. Blast has an excellent summary here:
http://intotheborderlands.blogspot.com/2008/01/homemade-wood-gasifier-stove-revisited.html

Of course, you don't have to have a wood gasifier stove - ordinary stoves works very well too. They're just convenient ways of setting fire to wood so you can cook and heat. You can keep them that easy - or you can gain efficiency by inventing more elaborate ways of controlling air flow.

What would happen if you used mag wheels? Are they really magnesium, or something else?

(Visualizing airline pilot: "WOW! Look at that signal fire down there!")

Sue

Magnesium tires take a lot of heat before igniting, I can't remember exactly, make the fire bigger by pumping water on it... preferably from a great distance.
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Edit: depending on fuels used using a mag wheel should be a last resort, should the mag wheel turn a healthy shade of orange.. DO NOT HIT IT, unless you want to signal an airplane, DO NOT USE WATER in an attempt to put the flame out, it will get hotter OR explode.

Best bet is to not use a mag rim, I've never caught anything more than steel wool and magnesium scrapings on fire, metal fires are extremely hazardous and often quite toxic.

> Usually made from bigger rims, but the same Idea.

Yep, looks like they're using bigger than compact car tires. Bigger the better.

If you want something really good for a fireplace, look to sailing ship technology. The best improvised fire ring I have seen was a mast-band from a wrecked schooner. Think of an circular iron band about five inches high 18 inches across and 1/2 inch thick. It probably won't ignite too easily.

Oohhhhhh... Susan, was this really the best place to suggest this?

*evil giggle*