Went back to the bike to go home and noticed straight away I'd got a flat. Took off the wheel and inspected the tyre inside and out...couldn't for the life of me see any holes in it (it's got some kevlar lining stuff, so seems to be doing its job). Checked the inner tube and it wasn't obvious where the puncture was. Anyway, I put the spare inner tube on and re-fitted. When I got home I checked the old inner and the puncture was right at the base of the valve...not repairable. I can't figure out how I got a hole in that place. Anyone had a puncture like this? What might have caused it?