Comment Re:Doesnt sound like much? (Score 4, Informative) 219
There is good reason for this. If you hit a tank with something that just explodes and rains shrapnel, the hit will just bounce off, maybe destroying the optics but that is about it. You have to pierce the armor, which you do by hitting it with something very heavy and slender (such as a rod of depleted uranium) traveling at high speed that focuses a bunch of energy on one point. The heat from the collision and spalling from the armor itself then destroys whatever is behind the armor.
This does not work for a truck. If you hit it with a KE round, the round will just sail right through it. If there is nothing vital (the driver, engine, fuel lines, etc) where the KE round happens to pass, then the truck will just keep rolling. That is why you hit it with HE or MG fire. The many small bits of metal from an exploding HE round have a much higher chance of hitting something vital than the single big chunk from a KE round.
As far as a tank is concerned, you usually only get one or two shots at it before it or its buddies start returning fire. If you hit it with the wrong ammunition, he is going to kill you.
It should be noted that the inverse is also true. Making vehicles such as a truck look highly armored increases their survivability in certain situations because AT rounds are rarer than lighter ammunition and an infantry squad with a machine gun is not going attack a tank.