Sure , smaller nomadic groups might make sense out of necessity . My point was more about the extreme distrust towards other groups and that it always seem to be justified , and that humans are clearly capable of working together in larger groups . Also , these are usually societies that are used to agriculture and a settled lifestyle . About cars , all postapocalyptic fiction I ' ve come across which even mentions motorised vehicles make a point about fuel either being scarce or the supply running out . Since bikes are so ubiquitous these days , I ' d imagine they would be used a lot . But bikes can ' t really as far as I know effectively pull heavy stuff , hence the need for horses or other beasts of burden when the fuel is unavailable .