I had a tire on my van (left rear) destroyed while towing my travel trailer last month. The reason for the loss was that the valvestem split at the point where it passes through the rim. The worst thing was that I had been flaged down at a traffic signal by another motorist just 2 weeks before that because the right front tire was going down. As it turned out the reason for the air loss was a valvestem spliting where it went through the rim. It cost only $6.00 to fix the first stem. The second one cost me the cost of a new tire (Michelin LTX $143.00 at Tire rack) plus the replacement spare that I bought while on the road. The replacement is a used Goodyear Wrangler that is the same as the new spare that I had on the van. I was lucky to find a great tire dealer in the form of the Ken Towery's Auto Care Super Centers 6609 Preston Hwy, Louisville, KY 40219. Matt was very tolerant of us and was able to to get us back on the road for less than $40.00. He remounted the spare that I had on to the aluminum wheel of the destroyed tire.Then mounted the replacement spare onto the steel spare wheel and replaced the other two valvestems. So as you can read the small things can really add up.