Take a piece of chalk in your underseat bag next ride and mark the tube before you remove it so you can see where it is leaking if you get a flat. Then look at that spot on the tire over the leak and see if you can find what caused it. If you don't get a flat, then carrying the chalk was clearly the cheapest solution ever. And count me as one who disagrees with all of the opinions about low pressure and wide tires. I used to be 265# (now around 240). I tried wider tires at lower pressure, and was measurably slower and still got just as many flats. If you ride a tire designed for higher pressures with a more supple casing, you can ride higher pressures without too much difference in ride quality. I ride 320 TPI Vittoria 23s at 135 psi and feel like I am flying compared to riding heavier tires at 115-120 psi.