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MotoGP God
Bikes: 748S, HM1100S, V4SP, Was: DD-A #111
Posts: 13,088
Join Date: Feb 2002
Location: Back in Essex
Mood: Passion Killer
Different bikes use different ratios to calculate the speed.
You need to make sure that the speedo ratio matches your bike otherwise it won't read the correct speed!
You'll need to do some investigation to find out what Ducati use (chances are they're all the same!) and buy the speedo with the correct ratio.