BUMPER INCLUDING NON-LINEAR SPRING

A vehicle includes a vehicle frame having a frame-rail end. The frame-rail end has a vehicle-forward face and a vehicle-rearward face. The vehicle includes a bumper vehicle-forward of the frame-rail end. A rod supports the bumper on the frame-rail end. The rod is fixed to the bumper and slidably extends through the vehicle-forward face and the vehicle-rearward face of the frame-rail end. A head is fixed to the rod and is retained vehicle-rearward of the vehicle-rearward face by the frame-rail end. A spring is on the rod. The spring has a non-linear spring rate.