i have a couple of thorn resistant tubes which i love (just thicker rubber) but they're hard to come by locally so i've been trying to patch the punctures. Without luck. Is it because I run the tires at 100psi or my own patching incompetence? I'm certain I've seen other people post about how they never buy new tubes because patching is just as good - are they running mtb tubes at 30 psi?