Aspects of the disclosure relate to adjusting a shear pin to minimize an impact force felt by an object in a collision with a vehicle. For example, one or more second computing devices may receive, from one or more first computing devices, information indicating that an impact with an object is imminent. In response to the received information, the second computing devices may determine a first shear force for a first shear pin, wherein the first shear force is a desired amount of shear force necessary to break the first shear pin. The second computing devices may send a triggering signal to activate an actuator prior to an impact with the identified impact target. The actuator, in response to receiving the triggering signal, may adjust the first shear pin in a first pinhole, so the first shear pin will break at the first shear force.