(Fortune Magazine) -- The tires we see are mostly used in gold and other strip-mining sites, so sharp rocks make the punctures. Running over a nail will not puncture these tires. The mine blasts create shards of rocks similar to the glass of a cracked window. Sometimes these rocks can be bigger than an average passenger car. I think the biggest tire we ever worked on was about 13 feet high and weighed upwards of 13,000 pounds. The tires cost about $25,000 each, and a patch might cost $200, so the repair is worth it. The biggest patches go above my waist and weigh five pounds. We attach them with special rubber cement. First you have to get inside the tire to take the liner out. You can move around, but you can't do jumping jacks in there. Sometimes we'll get tires after it rains on the mining site. The machinery will get trapped in mud, and the tires will spin and wear down. The tires are heavy, but they're also dirty. It's a dirty job.