HI, we have changed the 101 diffs and are using larger tyres than on the Disco too so we have a gadget which can adjust the speed readout. Yes, we are aware that the Disco sender emits 2x the pulses of the Defender. I have already replaced the Disco sender with a Defender (? bought by my son so don't really know) one. We are using the Disco sender on the bench to wind up the mileage. Lots of fun and head scratching going on. Thanks Lucy.