Although the advanced pedestrian legform impactor has successfully addressed a number of issues of the flexible pedestrian legform impactor, the large spring back during the rebound phase notably seen in impacts with low bonnet leading edge cars has not yet been resolved. The aim of this study was to improve the design of the advanced pedestrian legform impactor to address this issue without sacrificing its advantages. The heavier femur and the stiffer flesh of the impactor, compared to those of a human, were confirmed to be responsible for the spring back due to the accumulation and release of a large bending energy of the femur. To improve the response in the rebound phase, specifically for low bonnet leading edge cars, a bumper system was added to an advanced pedestrian legform impactor model to reduce the accumulated energy of the femur in proportion to the degree of the hip adduction angle. The validity of the system was evaluated in impact simulations with low bonnet leading edge car models. Its hardware was designed to realise predicted performance in car tests, while maintaining durability. The results of the functional tests show that the bumper design substantially reduced the spring back of the advanced pedestrian legform impactor in impacts with low bonnet leading edge cars, without sacrificing the impactor performance in impacts with higher bonnet leading edge cars.