Mining companies are complaining about a shortfall in the supply of the giant tires that go on large dump trucks and other heavy equipment. The tires are as large as 12 feet tall and 4 feet wide. The law of supply and demand has kicked in, and prices have quadrupled in the last year to more than $40,000 per tire.

[Read](http://www.nytimes.com/2006/04/20/business/20tire.html?ex=1303185600&en=504e2d14de26b70c&ei=5088&partner=rssnyt&emc=rss) (New York Times)