The back wheel of bike.3 is totally flat, and I don't know why. I checked the outer tire and found a thorn, maybe that's the reason. Tomorrow, I'll dive in and have a look see what the problem is.
What I don't understand, is that it was OK when I brought it back from my last day out, and it isn't a slow leak, it goes totally flat in a few hours.
A new inner tube is probably the answer; I have several of the very thick type that I got really cheap.