In order to analyze the steering returnability of motor vehicle at low speed, the kingpin offset at ground and castor trail were studied with graphic transformation when steerable road wheels were steered. Calculation results show that kingpin offset at ground varies little, but the castor trail changes obviously when the steer angle increases gradually. Castor trail of the outer wheel decreases gradually, and castor trail of the inner wheel increases gradually, which affect the steering returnability significantly. Tests were conducted, and the test results support the above calculation, which can prove the validity of the calculation method.