后倾角（英语：caster / castor angle）乃由汽车、机车、或自行车车身的侧面望去，大王销与悬吊系统（即地面垂直线）的夹角。通常负的后倾角代表着较佳的灵活度，正的后倾角则具有较稳定的直进性。简单来说，后倾角可看为车轮轴线与地面垂直线的夹角（对汽车来说，由于多连杆悬吊的设计日趋复杂，车轮轴线常以虚拟大王销轴线代替，可将车轮轴想像为一条贯穿上球型接头的中心点到下球型接头的中心点的线）。赛车手通常会借由调整后倾角，来优化车子在某些特定驾驶情形下的的操控性。

The caster angle or castor angle is the angular displacement from the vertical axis of the suspension of a steered wheel in a car, motorcycle, bicycle or other vehicle, measured in the longitudinal direction. It is the angle between the pivot line (in a car an imaginary line that runs through the center of the upper ball joint to the center of the lower ball joint) and vertical. Car racers sometimes adjust caster angle to optimize their car's handling characteristics in particular driving situations.