Today i was out on what was suposed to be a 30 minute ride, and it turned into 45 minutes because of the flat I got about a km away from home when i was trying to jump a curb (i have temporary horible platform pedals until i can find some bb's for my old ones). This is the second one this month and i dont understand why. im not useing especially cheap tubes. The preasure is around 50-60 psi, and im not riding especially demanding terain. They were both pinch flats, could it have something to do with the stock tires (bontrager) that came on my bike (a 2003 trek 4500). Any help apretiated.