We got a resistance trainer for Christmas and I've used it twice in the past three days. Both times the tube on the back tire has gone flat after using the trainer for half an hour. I ride a 2002 Trek 3000 with a kevlar tire on the back, if that has anything to do with the problem. Is there anything I can do to prevent a flat tire? Change the tire? Put the trainer at a different setting? Thank you for your help.