Even though the common term is "load levelers", the true purpose of those bars is to get the correct tongue weight for safe towing. Yes, they will adjust the rear end height of a tow vehicle but what you are adjusting in reality is the tongue weight. The appearance of a level vehicle does not insure proper tongue weight. The old rule of thumb is that proper tongue weigh should be 10% to 15% of a totally loaded trailer. It's easy to spot a vehicle with too much tongue weight. It's negative tongue weight people need to be concerned with but they'll know soon enough after they get on the road and look in the rear view mirror and their trailer is swaying back and fourth.