First I thought some punk kid was letting them down, but it's happened outside college and work, not just my flat. Is it something to do with the change in weather? An existing slow puncture exasabated by the drop in temperature? As far as I remember, my tyres were fine in the summer, now when I walk out to it on a particularly cold morning, I find the rear tyre has dropped 20 psi, having just filled them the previous day. Anyone else experienced this? And is there a solution that doesn't involve new tyres? At the moment I'm just glad I bought a double barrel footpump.