The standard RS 4x4 hubs have a different offset for the track rod ends. The RS track rod ends are are within a few mm of the discs when fitted, where as the XR track rod ends are 10mm inwards away from the discs. This gives you a bit more clearance when playing with other disc setups. One version will have a better turning circle than the other though. I have both sets here to compare & take pics if needed.