I've been riding my first road bike for 3 weeks so far doing about 3 rides per week and averaging around 25 miles on decent roads. Last night I came home from a 25 mile ride, washed down the bike etc and stored it in the garage which is clean and dry. I come in this evening and see that the bike has a flat front tyre. I took off the tyre and tube (which is still half full of air) but can't see any holes on first inspection. I will repair the tube properly later but am wondering how I could have got a puncture overnight in the garage as the tyres were perfect when I put the bike away last night?