Plugging a tire will damage it because air will get between the inner and outer layer and cause a rupture.
As long as the leak is not in the side wall, plugging a tire works quite well for small leaks such as those caused by a nail. I have had many a tire plugged with no problems.
According to an independent tire place I have been going to for years (a business so honest they even turned down a job because the customer did not need the service) only patch tires, not plug them, for the reason I stated.
Jeanette Isabelle
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I'm not sure whose twisted idea it was to put hundreds of adolescents in underfunded schools run by people whose dreams were crushed years ago, but I admire the sadism. -- Wednesday Adams, Wednesday