Do tyres have safety release valves? I placed a child seat (with child) onto the back of my Racer. I have Bontranger tyres - 200x35 and Specialized inner tubes. On our first journey i noticed after approx 15 mins my tyre had gone down quite a bit. I got off to have a look and it had almost totally deflated. I pumped them up again and returned home. At home i took the child off the seat and had to pump the tyres up again, thinking that i had a total blow out. That evening i had a look at the tyre again expecting to deal with a puncture but the tyre was still fully inflated? Can anyone explain to me what happened? Can tyres loose air if placed under too much pressure without having a puncture? By the way i have used the bike to and from work daily without any problems.