I like to carry a cotton ball in my seat bag. If I get a flat, I take off the tire and wipe inside. Anything sticking through the tire will catch some cotton ball and be really visible. I think I got that idea here. It's also better than sticking yourself on something sharp using your fingers.
A worn tire does not have to be worn down to the cords to be worn out, as was mentioned already, escalating flats are one sign the tire is tired.
I also only use cloth rimstrips (Velox for example) and not those plastic ones as they are prone to shifting right off of the spoke holes, and that's flat city for sure!
As for tire liners, I don't use them. They change the feel of the tire on the road, and not for the better, and add weight. A tire in good shape, mounted properly, with good condition tubes properly inflated and good rim strip, are all that is needed wheel-wise, to help prevent flats. As for flat resistant tubes, they make no sense to me. If something is in the wrong place at the wrong time and is strong enough to go through a tire, it can puncture the thickest tube.
Sometimes it's just bad luck.
Tzvia- rollin' slow...
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