Perimeter, Beam, Schnabel and Stretch Trailers

What is a perimeter trailer?

A perimeter trailer carries its load on an outer frame that can widen around it, instead of on a solid full-width deck. Trail King's TK160 Perimeter Expanding Frame grows from 12 ft to 20 ft overall, leaving 10 ft 8 in to 18 ft 8 in of clear space inside, and is rated 160,000 lb uniform or 150,000 lb in 16 ft. Trail King says its low deck height lets it "haul even the tallest equipment".

XL Specialized sells the same idea as a system. Its 130 DGX and 180 DGX double gooseneck expandables also open from 12 to 20 ft wide and are rated 130,000 lb and 180,000 lb distributed. The 130 comes with a 2-axle jeep and the 180 with a 3-axle jeep, each with a double gooseneck, a steer dolly and deck sections, and XL quotes a low overall height of 9 ft 10 in for easier loading.

The frame sets the permit before the load does. Closed, a TK160 or DGX is 12 ft wide, 3 ft 6 in over the 102 in federal width on the National Network (23 CFR 658.15), so every move is a width-permit move. In New York, one certified escort is required as soon as a load passes 12 ft; past 16 ft the move becomes a Type 1S superload with a police escort, and two-lane roads need three certified escorts. Opened to 20 ft, a frame sits right on Texas's line: anything wider and the carrier must physically inspect and certify the route in writing, and TxDOT's Houston District requires law enforcement escorts front and rear. Escort triggers in other states are on our pilot car and police escort requirements by state page.

How far does a stretch trailer extend?

A stretch trailer telescopes for loads longer than its closed deck. The models below open by 21 to 33 ft, and XL's 80 FDE flatbed reaches 81 ft overall, 28 ft past the 53 ft semitrailer New York allows on its qualifying highways. Closed, the 80 SDE and 80 FDE are 48 ft long, the same as XL's fixed 80 SD; the extension is what separates them from a regular step deck trailer or flatbed trailer. Talbert's 55SA TELE is listed with decks from 32 ft 6 in to 54 ft.

Fontaine's Xcalibur stretch flatbed and drop deck are left out: their own spec pages give two different deck heights and two different lengths for each model.

Read the rating together with the deck position. Fontaine rates the 55MX at 55 tons in 16 ft closed but over the deck length less 2 ft when open, and Talbert rates the 55SA TELE at 110,000 lb on a two-point rigid load base 14 ft long when retracted, or 4 ft shorter than the extended deck. A long rigid load bears near its two ends, so check the open rating against where those two support points will sit. Stretch double drops are compared with fixed wells on our double drop trailer page.

Opened, every one of these runs as an over-length load. New York holds a semitrailer to 48 ft, or 53 ft on qualifying highways (VTL 385(3)), and its escort rules start at 80 ft overall, a line the XL 80 FDE crosses fully open before a tractor is coupled.

Jeeps, boosters and steer dollies: how multi-axle trailers add capacity

Federal rules allow 20,000 lb on a single axle and 34,000 lb on a tandem (23 CFR 658.17), and state permits set axle-group limits of their own, so the way to carry more is to put more axles under the load. XL pitches its high-capacity detachable gooseneck multi-axles at loads over 120,000 lb, scaled with jeeps, boosters and dollies.

A jeep rides between the tractor and the trailer's gooseneck (XL calls a one-axle jeep a "joe dog"). Trail King rates its TK80J at 80,000 lb on 2 axles and the TK100J at 100,000 lb on 3, with double-drop-style versions at the same ratings. Fontaine's 302 Jeep for the Magnitude 55H and 55L Plus has 2 axles on a 50 in spread, an 8 ft width and a 55 in fifth wheel, and is used with the trailer's optional 23 in flipbox; Fontaine does not publish its capacity.

A booster pins on behind the trailer. XL calls a booster on a rigid spreader bar "East Coast" and a pivoting, self-equalizing one "West Coast", and Trail King says a booster adds axle spread "for legal hauling during restrictions and added weight capabilities during permit loads". Neither raises the trailer's own rating. Trail King's steerable TKHD-S (110,000 lb overall, 90,000 lb in 10 ft closed, 14 in loaded deck, 9 ft wide) can be ordered reinforced for a single-axle booster; its TKHDG-S (160,000 lb overall and in 20 ft, 17 in mini-deck) comes reinforced for a tri-axle booster.

Worked example: a Cat D10 ships at 111,739 lb with its blade, push arms and ripper off, which is 1,739 lb over the TKHD-S's 110,000 lb rating, so it steps up to the TKHDG-S class. On that trailer's 17 in deck the D10's 14 ft 3 in stack rides at about 15 ft 8 in: over 14 ft, so a New York move needs a height-pole escort, but under the state's 16 ft superload line. At 12 ft 4 in over the trunnions it needs escorts for width as well. Our D10 and D11 bulldozer shipping weights list what comes off and travels separately.

Build the jeep, trailer and booster as one system and you get setups like XL's Lightweight 13 Axle: a jeep, a 170 mechanical gooseneck trailer and a booster (60 West Coast, or a 60 Power Booster for the East Coast), rated 170,000 lb in 10 ft on a 10 ft wide, 30 ft main deck. XL markets it for wind turbine nacelles.

For long self-supporting loads the rear wheels leave the trailer altogether. Talbert's 6-axle steer dolly carries "bridge beams, steel girders" on a hydraulic bunk, with automatic and manual steering on 24 tires. Trail King's 120 LPSD-HS is rated 120,000 lb, 10 ft wide, with 60 in axle spacing and a hatbox that rotates 60 degrees each way, and XL's 6-axle dolly lets its load platform swing 70 degrees each way. Talbert and XL do not publish dolly capacities. To check what an axle group may legally carry for its spacing, use the federal Bridge Formula calculator.

Superload review, route surveys and police escorts

Plan for three extra steps once a load needs one of these trailers: an engineering review of the bridges on the route, a route survey and police escorts. In New York, a Type 1S superload adds a police escort booked 2 business days ahead, municipal letters, a bond and, once the load is 14 ft or taller, a route survey with utility arrangements; the full list is in our New York superload rules.

Each state draws those lines in a different place, so compare the superload thresholds by state before fixing a date. Surveys, escorts and police details are priced on top of the haul, as the heavy equipment transport cost guide breaks down. Carriers that run perimeter, schnabel or modular equipment can join HTS through the carrier setup packet.