CB900 Reverse Trike is heavier than CB900 Bike, and needs the extra gear between 3rd and 4th for acceleration. Locking one side of the differential gives 4 higher gears for cruising. May not be possible to use all of the higher gears anywhere but downhill. (Might pull the whole range downward so that acceleration is quicker, and cruising gears are more usable) A better diagram of the powertrain:
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