Bicycle Mechanics - tube blowing out...not sure why.

the last two tubes i installed with this tire have blown out within a few minutes of pumping up the tire. i have combed over the inside of the tire and have found nothing sharp and i've checked the inside of the rim as well. looks fine.

the only thing i can think of is that the tire was sitting flat for a while and thus it might be slightly deformed in one area, and when i pump it up (around 90psi) it might be pinching the tube and then it blows. is this a valid theory?

the tires have less than 100 miles on them, but one of them did sit flat for about 2 months as mentioned above.

More likely, your tire isn't seating snugly against the rim in one place. First, examine the bead of your tire all of the way around. If the bead has been damaged, the tire is toast no matter how few miles it has.

If the tire looks OK, before you install your new tube, put just enough air in the tube to give it shape. When you install the tire on your rim, be careful not to catch the tube under the tire bead. Pump the tire up to only about 25psi. Check the beads all of the way around on both sides. If the tire doesn't look concentric, deflate it and work on getting the bead to seat at the high spot. Since you have bad history with this tire, if it looks OK, pump it up to 50psi and repeat the process. If it's still OK, go to full pressure. If it was my bike, I'd test it overnight before riding on it.

Could you be pinching the tube when you are prying the tire back onto the rim? Is the tube being punctured on the side nearest the rim or nearest the tire?

This depends, of course, on the type of blowout. Is it in the same spot on the tube each time? Is it the same type? Can you elaborate on what the tube damage looks like each time?

Do you see a small puncture in the tube that's always in the same place? Maybe you just need better rim tape if that's the case.

Do you see a couple of small punctures right next to each other? I believe when you have a pinch tire, you see a couple of small punctures right next to each other- people say it looks like a snake bike. If that's the case, it's a matter of ensuring that you're correctly putting the tube back on the bike correctly and installing the tire correctly. When you repair the flat, best to partially inflate the tube and slide it inside the tire, then get one side of the tire fully over the rim. From there, slightly deflate the tube even more, then grasp the rim and work the other side of the tire all the way onto the rim. Once the tire is fully on the rim, then push the valve hard so it depresses into the rim and pull it back out. From there, it's just a matter of partially inflating the tire to a low pressure and checking the tire to ensure that the tube isn't sticking out anywhere over the rim, and checking the full tire to ensure that the tube is evenly distributed correctly over the rim. If you don't see any lumps around the tire, then continue to inflate the tire to the proper pressure. I usually slowly inflate and check the tire as I'm inflating just in case.

Koffee

Small side wall failures can cause this as well. It will just be a small slit in the side wall only visible under pressure. If you use the Grouch method(I inflate every tire this way, just in case) you will see it by the time you hit 50psi, so look close.