I know the thread is old - but it caught my eye. And, there is so much good advice - basically EVERYTHING is here! Look:
. . .The only real issue I have experienced with worn tires is that you can start to get flats... if I get two flats in a ride and the tire is worn I generally take that a cue to get a new set of tires.
The man has pegged it. A worn tire may not appear "worn out" (not all tread = gone), but more flatting is a super-good indicator!
Use it if its not damaged carry a spare tube. just remember the rubber has gone hard by now.
Aged rubber is harder. Racers used to "age" their tires for this reason. And, this changes the grip and wear characteristics.
Life is too short to ruin a good ride on a bad tire. New ones seem to ride so much better not sure if it's reality or all in the head??
Sage advice. It is reality, it is just not always as visible as we might expect.
As a precaution, I always carry something to "boot" a cut tire with - a piece of sidewall from a tire you're throwing out is ideal.
Good idea as an emergency measure. But ONLY as an emergency. Most club riders can ignore this advice, as a car ride home is not that far away. Long distance tourists, however, should
be prepared to "boot". BUT, the tire MUST be replaced, and SOON. Booting is only a temporary fix. Continuing to ride on a booted tire is to risk an explosive blowout. The rim, and therefore the bicycle (and YOU!!), are supported completely by the sidewall tension. Once you realize this, how much faith do YOU have in a patched sidewall? Seriously, I've only had to boot a sidewall once - when my tire was cut by a cinder in Wales. It went another couple hundred miles, and possibly could have gone farther - so "booting" can be effective. But, it is still temporary, and can be dangerous. Safety is a factor here, and if possible, as soon as possible, the tire should be replaced.
On the other hand, if I were one of these fellas in Central America, or Africa, who are receiving "bicycle aid" in one form or another, a booted tire might need to last for months, because there WAS no replacement. And, it might do that. I might, under those circumstances, risk the blowout. My travel speeds would be lower, and the financial cost of tire replacement higher (relative to my theoretical income), accordingly changing the risk to gain ratio. I could see a booted tire lasting for months. But that isn't the kind of riding that I (nor you, dear CN reader) typically do, is it?