Truck adjustment plays a considerable role in drifting on your skateboard. There is no fixed scale to determine the tightness of the truck. So, everyone uses their preferred tightness when drifting. If I have to answer this question, you should tighten the trucks just to the point where the smoothness is intact but without the speed wobble. Looseness allows you to make turns easily, a crucial aspect of skateboarding. However, extra looseness can also result in nasty falls frim speed wobble. So, it's best to stick to the tighter side.