Increasing the shock spring preload will give you a little more ground clearance...as well as stiffen the ride. Can't have one without the other I'm afraid. Ideally preload is used to set the ride height. That should be with it loaded with all the normal items including people and the suspension is set in the middle of it's travel. That's the total swing movement from top to bottom with the shock on or 50/50 meaning 50% of it's travel is up or compression and the other 50% is rebound or down. You can have a 60% compression and 40% rebound (60/40) position and still have an acceptable ride but going much farther causes CV joints to wear more quickly and break easier. The "angle of attack" is also important...that is the difference between the back and the front. So you set the rear first, then the front, measuring from the flat part of the skid plates just in front of the rear diff or gear case and just behind the front diff to the level ground. You want it...and again it's fully loaded..from level to not more then 3/4" lower in front.