Drop Deck Decisions

A Mac Trailer aluminum drop deck’s transition area includes the 90-degree step (upper left) and a large curved “radius” beneath the upper and lower decks (center). The radius evenly distributes weight and stress between the two areas. Here, I-beam-like flanges add strength to the curved members. Photo: Tom Berg

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When freight is tall, trailers that carry it must be short. That’s the reason for the drop deck, a variant of the flatbed or platform trailer. A “single drop” or “step deck” has a forward down-step and a main deck that provides another 20 or more inches of vertical space to accommodate large coils of steel and aluminum, outsized mechanical or electrical gear, farm implements, and aircraft engines, among other things. A “double drop” has an even lower deck and an up-step ahead of the rear tandem.

The low main deck lowers the center of gravity, which helps with top-heavy loads, noted Bill Wallace at East Manufacturing, one of the trailer makers HDT visited during the recent Mid-America Trucking Show in Louisville, Kentucky. The depth of a flatbed’s understructure tapers upward under its nose, partly to match the height of the tractor’s fifth wheel and because less strength is needed at the trailer’s front. Likewise, a drop deck’s underframe also tapers upward at the rear, which allows the deck to be closer to the ground. This also is because less strength is needed, and it adds space for tall cargo.

Because of a single drop’s low main deck, the wheels and tires are typically smaller than the usual 22.5-inch size, 19.5s or even 17.5s. But with a double drop’s high rear deck, the 22.5s, with their longer-lasting tires and brakes, can be used.

Drop decks are not needed for most freight. And drop decks cannot carry items like long pipes, except when fitted with …Read the rest of this story

Source:: http://www.truckinginfo.com/channel/equipment/article/story/2017/05/drop-deck-decisions.aspx