Impact forces develop at the wheel/rail interface due to the presence ofdefects in the running surface of the wheel and/or the railhead. This paperreports on wheel impacts caused due to permanently dipped rail jointscharacterised by high frequency impact forces of high amplifications ofstatic load that occur for a very short duration (P1 forces), followed byrelatively low frequency, lower amplitude forces (P2 forces) that occur for alonger duration. These impact forces are affected by the design ofcomponents adjacent to the wheel and the rail, namely the bogie primarysuspension and rail seat pads; the influences of stiffness and dampingcharacteristics of these components are investigated. A modified 3Dwagon-track system dynamics simulation model that accounts for defectsin track is used to obtain the impact force time series which is converted toimpact force factors and compared with a set of field measured datareported in the literature. A simplified equation for the determination ofimpact force factors due to dipped rail joints is also proposed andvalidated.