If you ride in hard, rocky terrain, you might notice that your knobs tear off quite easily, even if you're running the correct tire for the terrain.
To minimize this, drill a hole in the face of each knob with a 1/6" bit. To avoid going too deep, drilling in the tire's carcass, get some tape and wrap the drill, marking the depth in which you should stop.
Drilling the knobs helps get rid of excess heat, which in turn, greatly reduces the tearing of knobs.
Also, if your tight and don't like spending $130 on a new M12, you can grab an angle grinder and square off the edges of a worn tire, just don't go to deep:crazy: