In article ,
says...

Besides the obvious--cuts or gashes, threads showing--what do you
generally check to tell when it's time to replace a tire?

If a cut did not cut the casing, then that is no reason to toss a tire.
It's time to replace the tire when the casing is showing. If the tread
gets real thin, you will also start to experience more flats, so that can
also be an indicator to get new tires.
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Alex __O
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