It really depends on your toungue weight. That is the weight on the 4Runner from the trailer when you sitting still. A lot of times your boat manufacter will list those in their specs. The toungue weight for your 4Runner is 500 pounds. My guess is your rig is something like 385 pounds or so. It you get near the 500 pounds it will tend to sag, if it is over 500 pounds it will really sag. there are ways to adjust the tongue weight, but be sure not to make it too light as that will make the trailer sway.