Depends on your tires as well. I have a 18' trailhawk and the 18" kevlar tires ride worse than the 305/35/22 Pirellis on my summer wheels. The sidewalls are so stiff, even at 33psi they ride rougher than the 22's with 38psi. My wife even commented on it when i made the changeover back to the stock wheels a few weeks ago.
If you do decide to go down to 18" wheels, be careful on the tire choice or you might not get the softer ride you are after.
If you do decide to go down to 18" wheels, be careful on the tire choice or you might not get the softer ride you are after.