What if our vehicles, like the motorcycle, started out as a normal motorcycle and then we would put the extra plating or spikes on through upgrades. Same for the truck and it's spikes. My suggestion stems from the desire of wanting a normal looking hot (like the original Duke's Hog) concept art while also having the ability to put spikes on it to do extra damage to zombies (since I know a lot of ppl like the spikes on the front) or add plating for extra vehicle hp or defense.