Join Date: Jun 2002
Location: Auckland, Aotearoa, New Zealand
My wife gets car-sick at the drop of a hat as does my daughter. On a bike they are perfectly OK with no motion sickness. I believe this is because in a car, corners have us sitting upright with a sideways/lateral pull on the body which upsets the natural state of both the inner ear and the stomach. The combination of the balance going skew-whiff and the stomach getting dragged left and right produces the car sickness in those sensitive to this type of thing. There is often a strong psychological element as well (seen with small children some of whom can be told not to be car sick).
On any bike, there are no side/lateral forces as the bike's lean ensures cornering forces operate vertically along the body's axis. This leaves the up and down motions. On a Harley, it may well be that the more sedate ride has kept your passenger below her natural limit for the up/down oscillations over road bumps/wallows and whoop-de-whoops. The generally faster speeds on the LT may be just crossing the boundary she has.
Overall, I'd assume therefore its not the cornering, its the up and down motion thats affecting your passenger. Recommendation....go fast in the corners, slower in the straights.
From my own direct experience, the longer you spend on the bike, the more you become subject to the vibatory effects of wind buffeting. On really long days, I sometimes get off the bike feeling a bit sick with a bit of a stare in the mirror of the motel looking a bit blurred for a few minutes. Maybe you are spending longer on the LT than the Harley and this means more limits being reached?
Located: Auckland, New Zealand...
but I left my biking heart along the Scenic Byways of America.....
"Come fill the cup that clears
Today of past regrets and future fears." ....Omar Khayyam