Quote Originally Posted by madisongrrl
I had my rode bike in the back of my truck. We were mountain bike camping at the Kettle Moraine, WI in late September. It was very cold at night (jackets, pants etc.) and very hot during the day (shorts and tanks). I had pumped the tires up to the max (120psi), but I did it when it was cooler. We spent the day mountain biking and the rode bike was locked in the back of my enclosed truck, baking in the parking lot. Both tires were flat as a pancake (we actually heard one of them go).

My two questions are: Do you think the heat caused this or was it something else? How many psi's would it take to pop a tube in an average 23mm, 120psi max tire?
If you pumped to 120psi at 32 degrees and your truck went up to 120F sitting in the sun, that's an 18% pressure rise, or up to 142 psi. Not surprising that would blow tires. I believe that the pressure printed on the tire is the max you should ride at, though you don't necessarily need that much. There must be some margin above the printed max, otherwise tires would blow when you hit a bump while riding, but not sure how much. BTW, it's not the tube that's critical, it's the tire bead blowing off the rim, which will of course blow the tube because the tube then expands very suddenly. With tubulars, it's the strength of the stitching.