If you want to adjust them and they are adjustable, I would move them up and leave about 1/2 in clearance between them and bottom of boat. The only one that might ever come into play is the very first one at rear of trailer. Like everyone else said they are just there to keep you from hitting the frame. But on some hulls I have seen where just a slight V at front of hull could hit when running up on the trailer and trailer is a little to shallow and level. If it hits that roller it will help lift it up to the runners.