A precise analytic expression of self-aligning torque from vehicle kingpin inclination was given. The relation equation of front axle elevation with steered wheel angle, kingpin inclination, caster and caster offset at wheel center was inferred according to spatial geometry. The potential energy increasing of load on front axle was up to power to overcome the self-aligning torque from kingpin inclination when steered wheel angle was changed. The analytic expression of self-aligning torque with steered wheel angle, kingpin inclination, caster and caster offset at wheel center was got by calculating derivative of potential energy increasing of load on front axle by steered wheel angle. Finally, the elevation of front axle was tested when steered wheel angle was changed on an experimental vehicle. The results show that the testing data agrees well with the theoretical calculation results, and the analytic expression of self-aligning torque from kingpin inclination is correct and reliable. 