I am currently riding a 700x28 Specialized All Conditions tire on my front wheel and last week I took a close inspection to see how it was holding up. It's currently full of a zillion tiny holes, from I know not what. I do have glass on my route because I ride in traffic but I've never seen tire tread to this. On the other hand I haven't had any flats because of it either. I haven't replaced the tire and probably won't until it gets closer to failure.