I agree with Cougar. Fourth gear is the best when pulling heavy load. I ride fourth gear even when I don't pull my trailer. (aluminum) I have the 09 RSV Hannigan kit, and there is plenty of power in the fourth gear. I discovered the the fifth gear (overdrive ) performs best at speeds of 75 and above. <br />
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I do run 4th gear at 75 and it still have plenty of power to continue - but I usually will shift to the fifth. As far as power is concern - there is plenty of power in the V4 1300 engine. I'm able to keep up with most of the trikes. <br />
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You won't be disappointed with power except starting off in the first two gears. The weight (320) added to the trike does make it sluggish in those gears.
I usually ride 1 up and the first two gears don't exist as far as I'm concern. I ride slow on roads with traffic lights so I don't have to stop to often.<br />
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Anyway - whatever you do - enjoy the bike and be safe.