Specialized & heavy haul
Specialized & Heavy Haul Trucking Services
Step deck, double drop, lowboy and RGN freight through carriers in our network, generally up to about 150,000 lb, with state permits coordinated.
A machine 10'5" tall in a 20 in well stands 12'1", 1'5" under 13'6" (most states). On a flatbed's 5 ft deck it would stand 15'5" and need a height permit.
What we move
Freight that is too tall, too wide or too heavy for a van or a flatbed. Carriers in our network run step decks, lowboys, RGNs, multi-axle and extendable trailers; our specialized desk matches the load to the trailer and coordinates the permits.
- Step deck, double drop, lowboy and RGN capacity through carriers in our network
- State permits coordinated for each state where the load is over the legal limits
- Loads generally up to about 150,000 lb on multi-axle equipment, under permit
- Priced by our specialized desk from your dimensions, weights and photos
A load needs permits when it's over 8'6" wide, over a state's legal height (13'6" to 15', set by each state), or over 80,000 lb gross or any axle limit. Each state's limits
Trailer options
Each one sits lower or carries more than the last. The trailer guide has the full spec sheets and a check of your load against each state's height.
Lower deck 36 to 42 in · about 10' of freight
For freight a flatbed can't clear. Loads by forklift, crane or ramp, and often moves without a height permit.
Well 18 to 24 in off the road, 24 to 30 ft long
A low well between a raised front deck and the rear axles, for the tallest freight. Loads into the well by crane or forklift.
Well 18 to 24 in · 26 to 30 ft · up to about 12' of freight
A lowboy whose neck comes off, so the deck front lowers to the ground and a machine drives on under its own power.
Added axles for weight, extendable decks for length
Jeeps, boosters and spread axles carry heavy loads over more of the road to keep each axle legal; stretch decks extend for long pieces.
Specialized trailers explained
How lowboys, RGNs and spread axles work, where a load's weight goes, and when a load needs a permit, in 12:33.
Heavy haul in depth
How heavy-haul trailers work
Heavy haul is a height problem and a weight-per-axle problem. Trailers drop to clear the legal height; axles get added and spread to stay within axle limits and the bridge formula; past a point, states call it a superload.
Goosenecks
How a removable gooseneck works
Lowboy names the shape: a double drop with a low well between the neck and the rear axles. Fixed, mechanical and hydraulic name the neck. An RGN is a lowboy whose neck comes off, so a machine can drive straight on from the front.
Park the tractor and trailer in a straight line on firm, level ground.
The most common in heavy haul. Cylinders raise and lower the deck, powered by the tractor's own hydraulics (a wet kit) or a small engine in the neck (a pony motor).
Ground-bearing or not
You'll see “non-ground-bearing” on spec sheets. It says how the neck gets its lift.
Capacity
What a 55-ton rating means
On a normal road, less than you'd think. The rating tells you what the frame can hold. The road limit decides what it can carry without a permit.
A strength rating, measured with the weight concentrated in a 12 or 13 ft span of the deck, depending on the builder. It describes the frame, not what the road allows.
Everything above that takes permits and more axles. Added axles don't make the trailer stronger. They make the load legal by spreading it over more of the road.
Weight distribution
Where the weight goes
Think of the trailer as a beam with two supports: the kingpin at the front, which sits on the tractor, and the trailer's axles at the back. A load is shared between them by distance. The closer it sits to one end, the more that end carries.
At 18 ft the drive axles carry 45,338 lb, over their 34,000 lb limit, and the trailer axles carry 38,750 lb. The total is 97,000 lb wherever the machine sits, so no spot on the deck makes this load legal. It needs a permit and more axles.
- Excavator 55,000 lb.
- 40 ft from the kingpin to the center of the trailer axles.
- Tractor wheelbase 20 ft, fifth wheel 1 ft ahead of the drive axles, so 95% of the kingpin load goes to the drives.
- Tractor empty 20,000 lb: 11,000 on the steer, 9,000 on the drives.
- Trailer empty 22,000 lb: 8,000 on the kingpin, 14,000 on its axles.
- Trailer axle limit: 3 axles 9 ft first to last, 42,500 lb by the bridge formula.
In this example the drives drop under 34,000 lb only once the machine sits about 26.7 ft back, and by then the trailer axles carry about 50,700 lb.
Axle limits
Axle limits and the bridge formula
On the Interstate, three numbers set the baseline. Congress set them in 1975 and added the bridge formula at the same time, because a bridge feels how much weight is packed into each foot of truck, not just the total.
- W
- the most weight the group of axles may carry, to the nearest 500 lb
- L
- feet between the first and last axles of the group
- N
- the number of axles in the group
A standard five-axle tractor-trailer needs about 51 ft from the steer axle to the last trailer axle to carry the full 80,000 lb. One exception: two tandems in a row may carry 34,000 lb each when their first and last axles are at least 36 ft apart, where the formula alone gives 66,000.
Adding axles
Spread axles, jeeps, boosters and flip axles
To carry more legally, add axles or spread them out. Build a combination and see how each axle group is held.
| Group | Axles | Spacing | Limit | Why |
|---|---|---|---|---|
| Steer | 1 | one axle | set by state | No federal 12,000 lb limit; states cap it at 20,000 lb or the axle rating |
| Drive axles | 2 | 4 ft 4 in | 34,000 lb | tandem, 52 in apart |
| Trailer axles | 2 | 4 ft 1 in | 34,000 lb | tandem, 49 in apart |
Without a permit the gross stays at 80,000 lb on the Interstate, however many axles. Above that takes an overweight permit from each state on the route.
Why spread axles carry more
Push two axles more than 96 in apart and they stop being a tandem. Each becomes a single axle, good for 20,000 lb, and the pair answers to the bridge formula: 40,000 lb at 10 ft apart, against 34,000 on a closed tandem. Just past 8 ft it is only about 38,000.
- The 36 ft tandem exception doesn't apply to a spread, so a spread-axle trailer passes the formula on its own numbers.
- Spread axles scrub their tires in tight turns.
- Many states limit the distance from the kingpin to the rear axle. California, for example, holds trailers over 48 ft to 40 ft from the kingpin to the rearmost axle.
- States set their own spread rules too, so check every state on the route.
Jeeps, boosters, stingers and flip axles
- Jeep
- An axle group between the tractor and the trailer. The gooseneck hooks to a fifth wheel on the jeep, which takes part of the kingpin weight off the tractor's drive axles.
- Booster, or stinger
- An axle group pinned to the back of the trailer; the name changes by region and builder. Many hold their share with nitrogen: cylinders press against a nitrogen-charged accumulator that acts like a spring, so the axles keep their set load as the road rises and dips.
- Flip axle
- A single axle pinned to the rear that flips up onto the trailer when it's empty, keeping the rig short and the tires off the road.
- Steerable axles
- On long trailers the rear axles can steer, on their own or with hydraulics, so a long combination makes a corner without dragging its tires.
- Not the same thing
- A stinger-steered car hauler is a federal term for a car carrier whose hitch sits behind and below the tractor's rear axle.
Michigan has allowed up to 11 axles and 164,000 lb since 1967, because what wears out a road is the load on each axle, not just the total.
Permits
Oversize, overweight and superloads
A load needs a permit from each state on the route where it passes any of these. Routine permits are often issued online the same day.
Each state sets its own line. Three examples:
160 ft long
201,000 lb gross
135 ft long
17 ft high
over 254,300 lb
gross
Superloads can need route surveys and bridge engineering reviews, and take weeks to approve.
- around 12 ft wide1 pilot car
- around 14 ft wide2 pilot cars
- around 16 ft widepolice escort
Common thresholds; they vary by state. Most states also limit oversize moves to daylight, and many restrict weekends, holidays and rush hours.
Each state's legal limitsThe far end
The biggest rigs
Past the multi-axle lowboy, the trailer starts to wrap around the load.
Simplified models; the green block is the load.
- 294 tons
- the whole superload
- 213 ft
- long, taking two lanes
- ~400 mi
- mostly on I-80, mostly at night
The load: an empty steel tank from a decommissioned prototype reactor.
When specialized & heavy haul is the right choice
Step-deck, lowboy / RGN, double-drop, extendable, and multi-axle trailers handle loads that exceed standard van and flatbed limits. Pick specialized when the load needs a permit or a lowered deck, not for routine open-deck freight. Freight that's just too tall for a flatbed often fits a step deck without a permit.
- •Cargo is over 8'6" wide, over a state's legal height (13'6" to 15'), or over 80,000 lb gross, so it needs permits
- •Step-deck, lowboy / RGN (removable gooseneck), double-drop, or extendable required
- •Construction equipment, industrial machinery, transformers, turbines, or modular structures
- →Standard dimensions, weather-sensitive cargo: dry van
- →Standard dimensions, open-deck OK: flatbed (faster and cheaper than specialized)
- →Temperature-controlled: refrigerated (reefer)
- →Less than truckload quantity: LTL or partial truckload
Start the quote with these ready
The quote wizard takes the pieces, weights, stops and dates; our specialized desk prices the move from there. Having these ready makes it faster:
What shippers say
Feedback from customers who move specialized and heavy-haul freight with us.
“Freight Sidekick is a great company!! Katie, the dispatcher, communicated the driver’s location throughout the trip from Los Angeles to…”
“They've been nothing short of fantastic to worth with so far.”
“Excellent prices, and good communication with the shipping company.”
Frequently Asked Questions
Common questions about Specialized shipping
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