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Dip, but hold the chips

Trailer angle dip refers to the point when the trailer top corner hits the top of the sleeper. To assist with envisioning this, think of a tractor being towed by a wrecker, while the trailer was still coupled to the tractor. The squeeze effect presented at the top of the semi-combination junction represents what we refer to as dip angle.

Dip angle must be calculated to ensure that on undulating ground there will be no interference.

The inputs are influenced by the trailer design, coupled with the height of the day cab (with or without roof fairing), or sleeper height (with or without roof fairing). The taller the roof heights and the smaller the trailer gap, the smaller the actual clearance angle becomes.

But this is not limited to trailer characteristics, the load also can be a consideration. Loading a flatbed can depend on where the load is positioned on the trailer, and how tall it is at the corners. If the load measures 13’ 6” (from the ground), then it is treated much like a van trailer. When spec’ing flatbeds, it is important to provide negative 5th wheel settings to allow for loads that are positioned forward of the trailer nose. This loading style is frequent when weight distribution is not a concern.

Engineering assumes a 5-6 degree angle for calculating Dip Clearance. The tangent of the angle multiplied by the load/trailer height above the 5th wheel plate will give the inches of clearance you will experience. Any positive number provides that you will have clearance.

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