| Going up teeth on the rear will bring down your top speed, but improve the acceleration of the bike, because you're "squeezing" the output of the bike into a shorter range.
This has the side effect that you will alter the revs you are doing at certain speeds. For example, on my 748 it wouldn't sit happily at 40mph because it was too high for 1st (screaming) and too low for 2nd, in that it kept spitting and missing and generally running poor.
This made town traffic a nightmare. Changing the gearing move the range of the gears so that 1st is shorter, but in 2nd it now runs lovely at 40mph because it's slightly higher up the rev range and runs much better.
If you go the other way of removing teeth from the rear, you're making the gears "longer" and increasing the top speed, but obviously it will reduce the acceleration.
This topic has been discussed many times before and it's generally accepted that dropping to a 14t front from an original 15t (equivalent to going up 2 or 3 teeth at the rear) is the best and cheapest (a new front sprocket is about £15 from Ducati) modification you can make to most of the Ducati range.  | 
antonye
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