I recommend any race car suspension book. Shock settings is one of those things that is a large part black art, especially on a 3 wheeler. It depends on what you are looking for on any given conditions. Example , on a rough road, soft is good as the shock will let the suspension rise and fall quickly with the bumps. Or on a smooth road, a stiff setting will give you crisper handling as the car has less tendency to roll and dive with sudden inputs such as turning and braking. Mostly you will need to just try different sittings and see what feels best for your driving style. I recommend starting soft, as did Colin Chapman with his Lotuses.