They used to make a little wire "dealie" that you attached to the frame and it dragged over the surface of the tire to knock off any glass, pointy rocks, tacks, or railroad spikes that you picked up as you ran over them. That way they didn't get a chance to work their way through the tire and into the tube. Obviously, the trade off was a little more drag. I am not sure that they even make them anymore, but they worked great.