Erratic readings on my 02 ce model, was a broken speedo magnet. unfortunately Triumph dont sell the magnets separately, you got to buy the whole unit at £100+ (ripoff).
Any way I modified mine, the speedo is expecting 4 pulses per 1 revolution of the front wheel, so I glued on 4 small magnets to the front disc and mounted a bracket for another sensor works great up to just over 100mph then the pulses get a bit fast for the sensor to pick up. But at normal road speeds it works a treat.