Another downside to "slime"-type tire repair is the possible hazard of the tire rupturing when it gets too hot. I'd have said it was just a wive's tale until I personally saw it happen.

My girlfriend's father has an old, small car that he shows in car shows. The tires are a little bigger than a bicycle tire.

He had the car sitting out in the sun at a car show one day, it was maybe about 90 degrees, and the tire went off like a grenade. It actually blew a chunk out of the rim. We were standing maybe 20 feet from it when it happened. Turns out he had just put the slime-type stuff in there a few days before the car show.