What happens when you apply the brakes aggressively while towing a fifth wheel trailer? Does the front of the trailer push down on the hitch and the rear axle of the truck? To find out, I ran a simulation in Carsim 7, using a full-size pickup model, and a model fifth wheel trailer. The loaded truck in the simulation weighs approximately 5600 lbs, and the trailer about 6500 lbs. Yellow tire force arrows show how much weight is on the tire during the braking event (the vertical arrows), and how much braking force the tires are providing (the arrows pointing to the rear).
The results of the simulation show that the truck is able to stop much more quickly than the trailer, even with properly adjusted trailer brakes, so the trailer actually pushes forward on the hitch. Combined with the forward weight transfer of the truck itself, this means weight on the rear wheels decreases significantly under hard braking; enough that the truck’s ABS is activated for the rear wheels.
Video: Weight transfer during hard braking. Yellow arrows
show weight on each tire during hard braking. Brakes applied at 0:17.
There is some weight transfer from the trailer axles to the king pin under braking. To model this, I simulated how the trailer would behave without any truck braking. This would be the situation if the truck brakes failed for some reason, and the driver used the trailer brakes alone to stop the vehicle.
In this video, only the trailer brakes are being used.
Brakes applied at 0:13.
The results of this simulation show that there is some forward weight transfer of the trailer under braking. The force on the rear axle of the truck does increase when only the trailer brakes are used.
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