per their website:
Longer Wheelbase
We increase the wheelbase 8". This puts the rear wheels back behind the passengers’ seat area rather than sitting right on top of the wheels. Any vehicle that has a longer wheelbase will have a smoother ride, it’s just common sense. As an added benefit, the differential being farther back reduces the driveshaft angle.
Trikes: HT1800 : Roadsmith Trikes
but maybe they are mistaken!!
This is for from the HDTR kit on the web site.
Longer Wheelbase
We increase the wheelbase of this bike by 10". This puts the rear wheels back behind the passengers’ seat area, Rather than sitting right on top of the wheels. Any vehicle that has a longer wheelbase will have a smoother ride. It’s just common sense.