Borrowed a friend hardtail while mine is being repaired. I keep presta tubes in my Camelback, and it turns out the rear tire of the bike I am riding has a schrader tube. Of course I got a flat while riding. I changed the tubes and actually rode the rest of the ride with the tube with no problems. Today, I flatted out three times. My assumption(always a bad thing) is that the tubes are not compatible with the wheel. Am I right in this assumption? I know this seems trivial, but I want to know the answer. Thanks in advance for any replies.