The different torsion bars have different ways of pre-loading them. I have the trunnions type which get their pre-load by the height and angle of the tow ball. The chains type, just require more links. When I set mine up, I leveled the trailer and measured the distance from the hitch (where the ball would support) to the surface of the street. This was right at 18". I then set up the bars per the instructions that came with the WDH. I then measured the distance from the top of the rear wheels to the lip of the fender well, I did the same for the front wheels. Then I hooked up the trailer and re-measured. I think the front end dropped 1-2 inches and the rear 2-3. I'm not sure as I don't remember exactly. I run about 10-15 PSI in the air bags and they help a lot when going up and down driveways and varied terrain. I've towed with both the airbags and without and definitely prefer the bags but I know that if they leak, I'm still OK.