You hitch up your trailer, walk around to check the lights, and notice something off. One side sits lower than the other, or the whole rear end looks like it's slumping. Sagging trailer springs are one of the most common suspension problems, and one of the most overlooked. Left alone, a sag does more than spoil the look of your rig. It changes how the trailer tows, wears out your tires, and can lead to a dangerous failure on the road.