bicycles!So I bought this rather nice bike from the pawn shop for a song, when I needed a new bike.
But the previous owner didn't maintain it very well, or at all. There was some wear on the sprockets, and he had ridden it flat once or twice, because there were tangential wear seams on the rear tyre walls.
You see, when you ride on flat tires the side walls will crease, because geometry. If you ride it flat long enough the repeated cyclic loading will gradually wear through the material. The previous guy did it often enough that the reinforcing fibers were exposed, which wasn't good. But hey, it Just Worked, and that's all I needed.
A month or two ago I got a flat and had to walk the bike home with the tyres dead flat. At some point, or shortly after, the seams wore through. I got a new inner tube and rode that for a while, until it got low and I tried to pump it up again.
Bam! The inner tube material had bulged out through the wear seams and consequently popped like an overinflated balloon. If I had watched it like a hawk I probably could have gotten away with it, but it would have failed a week later. Inner tubes are constructed as cheaply as possible, and will fail quickly with UV exposure, abrasion, etc.
So now I need a new tyre and inner tube.