Had another KA-POWIE! today. We were going under a freeway underpass at the bottom of a fast descent and the front tire blew right off the rim. Impressive noise. Rim was warm to the touch, no more. It looked like the tube split along one of its seams and that blew the tire off the rim. Old tube, maybe defective? Don't think it was a pinched tube. Put it in about 50 miles ago. Probably that little bit of added heat was more that it could take. Got it stopped fairly quickly, stayed up. Tire was perfect except for the damage caused by the rim running on the side of the tire that was off the rim. Rim was a bit trashed, warped, dings on the edge, and one spot kind of pooched out. Probably dropped onto the pooched out spot when it blew. Brakes were working perfectly, so nothing was wrong with the rim before. Plenty of wall thickness. One of those things. Bent the rim back to more or less OK with my chain tool, messed with the spokes until it would make it through a loosened up front brake, put on the spare tire (you carry a spare tire, right?), and we were on our way. Front brake was grabby on the bent rim, so we just took it easy and gave ourselves room. New rim ordered. Tire was only 50 miles old too, bummer. That's the third use of our spare this winter. Once for a loaner to a fellow tandem, twice for us.