From publisher blurb:
Certain gangs, road-oriented communities (e.g. "nomads"), and even individuals commonly modify their vehicles to maximize their performance not only on the road, but in battle. Merchant clans, motorcycle gangs, and indeed individual members of the Road Warrior and Raider advanced classes all have reason to invest as much in their vehicle as in themselves.
Rolling Thunder is a short supplement for Darwin’s World 2nd Edition that starts with a brief venture into modifying vehicles (in the fashion of many classic post-apocalyptic movies), offering just a few of the possible modifications characters can make to their vehicles to improve them for vehicle-borne encounters and adventures. Rolling Thunder also introduces a few new vehicle-themed weapons, and a number of sample vehicles commonly seen on the Twisted Earth, but adaptable to any post-apocalyptic campaign setting.