Lowboy Trailer Dimensions and Deck Heights

What is a lowboy in trucking?

In trucking, a lowboy is the trailer for machines too tall for a flatbed or a step deck. A 48 ft flatbed stands about 58 in at the deck (Utility 4000S: 58 3/16 in on a 47 in fifth wheel), which leaves about 8 ft 8 in for the load under a 13 ft 6 in limit. The lowboys below leave 9 ft 11 in to 12 ft. Of the heavy haul trailer types, it is the one built around deck height.

The lowboy truck is the tractor, and a lowboy truck and trailer have to match: Fontaine's Workhorse 50 and Trail King's HDGs are built for a 50 in loaded fifth-wheel height, and Eager Beaver sells its fixed GLB necks in six lengths from 82 to 102 in. Lowboy trucking is the carrier work of loading, securing and hauling on one; HTS books those carriers and does not run trailers of its own.

Every lowboy here has a gooseneck, the raised front that rides on the tractor. How a machine gets on depends on the neck:

• Fixed gooseneck. The neck is part of the frame, so the machine climbs a beavertail and ramps at the rear. Eager Beaver's 25 GLB and 35 GLB rate 25 and 35 tons on an 18 ft deck (19 to 25 ft optional) at 32 and 36 in loaded; the 3-axle 50 GLB-3 oilfield model rides at 43 in.
• Fixed neck, double drop. The deck drops behind the neck and rises again over the axles, leaving a 29 ft main deck on Talbert's 30-55 FG (18 in loaded) and XL's 80 Double Drop (18 in, basis not stated). The double drop trailer guide covers the rest of that family.
• Folding gooseneck. On XL's Hydraulic Folding Gooseneck, cylinders fold the front of the neck down at its hinge points into a front loading ramp, and the neck never leaves the trailer. XL rates it 100,000 lb in 10 ft on a 26 ft main deck.
• Detachable gooseneck. The tractor pulls the unlocked neck away, the deck's front end comes down to the ground, and the machine climbs on from the front. Of the 15 models here, 9 work this way, at 20 to 24 in loaded (26 in on the XL 160 HDG, basis not stated). That design is the RGN trailer, and its detach and hookup steps have their own guide.

How tall is a lowboy trailer from the ground?

Loaded, the main deck of a detachable or double-drop lowboy sits 18 to 24 in off the ground on the models we compared, and a fixed-gooseneck lowboy sits 32 to 43 in. Under the deck there are 6 in of road clearance on the Talbert, Fontaine and XL 80 models and 8 in on the Trail King HDGs and the XL 160 HDG. These are the makers' loaded figures, the ones that count with a machine aboard; none of them publishes an empty deck height.

The deck is not the trailer's highest point. Over the rear axles the frame stands 36 in on the Talbert 35CC, 37 in at the bolsters and 41 in at the main beams on the Talbert 55SA, 40 in on Fontaine's Workhorse 50 and 50 5/8 in on the Magnitude 80, so anything that rides over the wheels starts from there. Up front, the neck sits on the tractor's fifth wheel at about 50 in.

The math is legal height minus deck height: 162 in less a 20 in deck leaves 142 in, or 11 ft 10 in, for the machine. Air-ride setting, deck deflection and blocking move the real number by inches, so a machine within 2 in of the line gets measured on the trailer before the move is permitted.

How much can a 55 ton lowboy haul?

On its frame, 110,000 lb concentrated on a short length of deck: Trail King rates the TK110HDG at 110,000 lb in 12 ft, and Talbert rates the 55SA at 110,000 lb in half its 25 ft deck. On the road without a permit it is much less, because the 80,000 lb federal gross limit includes the tractor and the trailer. The 55SA weighs 20,850 lb empty, which leaves 59,150 lb for the tractor, fuel, driver and machine together.

Axle limits come before the gross: 20,000 lb on a single axle and 34,000 lb on a tandem under 23 CFR 658.17, with the bridge formula for longer groups (run the spacing through our bridge formula calculator). Heavier loads need an overweight permit, which states issue only for nondivisible loads: ones that cannot be split without ruining their use or value, or that would take more than 8 workhours to dismantle (23 CFR 658.5).

The tons in a model name are not comparable across makers. Fontaine rates its Workhorse 50 at 50 tons in 12 ft and 52 tons in 16 ft; Eager Beaver lists the 35 GLB at 70,000 lb with no length basis and a GVWR of 82,295 lb; Talbert sells the 30-55 FG at full capacity evenly distributed. Capacity also costs payload: the 25-ton Eager Beaver 25 GLB weighs 11,600 lb and the 80-ton Fontaine Magnitude 80 37,620 lb. Past the 80-ton Magnitude 80 and XL 160 HDG, loads move to the multi-axle and modular designs in specialized heavy haul trailers.

Width, weight and permits on a lowboy load

A lowboy's 8 ft 6 in (102 in) deck is exactly the federal width limit on the National Network (23 CFR 658.15), so a machine wider than the deck is a width-permit load. New York's statutory width is 96 in, with 102 in on qualifying and access highways (VTL 385). Outriggers carry the overhang: Talbert's 35CC and 55SA have 12 in swinging, removable outriggers, and Fontaine fits the Workhorse 50 with brackets for 12 pairs of swing-out outriggers and a hook-on pair.

Most machines in the fit table are wider than the deck before height comes into it: a Cat 320 ships 10 ft 5 in wide, a Cat D6 8 ft 10 in over its trunnions with the blade off, a Komatsu D61PXi-24 9 ft 10 in over its tracks. New York adds a certified escort over 12 ft wide; other states' escort lines are on our pilot car requirements page, and each state's permit office, fees and limits are under oversize permits by state.

On height, 18 of the 28 states we track set 13 ft 6 in; eight states, including California and Texas, allow 14 ft and Colorado and Nebraska allow 14 ft 6 in. Over 80,000 lb gross, or over an axle limit, the load moves on an overweight permit. The federal and state baselines are summarized in legal load limits.