What is Trailer Landing Gear? (Part 3)

How does Landing gear work?

From the outside, trailer landing gear looks relatively simple: steel legs, a gearbox, a shaft, and a crank handle. But inside is a mechanical system designed to convert rotational force into controlled vertical movement. That mechanical advantage allows an operator to support and adjust thousands of pounds of trailer weight without having to directly lift that weight.

Understanding how the system works also explains why commercial trailer landing gear looks and operates so differently from the simpler trailer jacks and support legs found on many light- and medium-duty trailers.

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  Landing gear in the morning. TurnNBurn adapter.

The Main Parts of Commercial Trailer Landing Gear

Although designs vary between manufacturers, conventional heavy-duty landing gear generally contains several key components:

• Crank Handle — provides the operator's rotational input.

• Input or Crank Shaft — transfers rotation from the crank handle into the gearbox.

• Gearbox — transfers rotational force and provides different gear ratios.

• Cross Shaft — connects the two landing gear legs so they can operate together.

• Landing Gear Legs — telescoping structures that extend toward or retract away from the ground.

• Internal Lifting Mechanism — typically uses gears and a screw-type mechanism to convert rotation into vertical movement.

• Foot Plates or Sand Shoes — create the contact point between the landing gear and the ground while helping distribute the load over a larger area.

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Together, these components create a relatively simple but extremely effective mechanical lifting and support system.

What Happens When You Turn the Crank?

Everything starts at the crank handle. When the operator turns the crank, that rotational movement travels through the input shaft and into the landing gear gearbox.

The gearbox transfers the rotation into the internal lifting mechanism. Inside the landing gear leg, rotational motion is converted into linear—or up-and-down—movement, causing the telescoping leg to extend or retract.

On a typical dual-leg commercial system, a cross shaft connects the driven leg to the opposite landing gear leg, allowing one crank handle to operate both legs at the same time.

Turn the crank in one direction and the legs extend toward the ground. Turn it in the opposite direction and they retract toward the trailer.

The result is a system capable of precisely controlling the height of the front of a commercial trailer.

The Secret Is Mechanical Advantage

The key to understanding landing gear is mechanical advantage.

An operator obviously couldn't walk up to the front of a loaded semi-trailer and physically lift it several inches.

The landing gear doesn't eliminate that weight. Instead, its gears and internal screw mechanism allow the operator to apply a smaller amount of force over a much greater number of rotations.

In simple terms:

Less force per turn + more turns = the ability to move a much heavier load.

It's the same basic engineering principle behind many jacks, winches, gearboxes, and other mechanical lifting devices.

And that brings us to an interesting difference between commercial landing gear and some of the simpler support systems we discussed in Part 2.

💡 Fun Fact: Why Use a Crank Instead of Just a Pin?

Some trailers use slide or drop-leg supports where one section of the leg slides inside another and a steel pin locks the leg at the desired height. So why don't heavy commercial trailers simply use a large pin? Because the two systems perform different jobs.

A pin-style support can be extremely strong when properly engineered and rated. Once the pin is inserted, the trailer's weight is transferred through the leg, pin, pin holes, and surrounding structure. But the pin itself provides essentially no mechanical advantage for lifting the trailer.

If the support needs to be repositioned while significant weight is resting on it, the trailer normally has to be raised or supported by another means before the pin can be moved.

Crank-operated landing gear is different. Its gearbox and internal screw-type lifting mechanism allow the landing gear to support the trailer while also making controlled height adjustments under load. That's a major distinction:

A pin primarily locks a support at a selected height. Crank-operated landing gear can support the load and mechanically change that height.

This is one reason crank-operated landing gear is so well suited to commercial semi-trailers. It isn't simply a trailer stand—it's an adjustable mechanical lifting and support system.

And there's an important misconception worth clearing up: crank-operated landing gear doesn't automatically have a higher static weight capacity than every pin-style support. Properly engineered pin-supported legs can carry substantial loads. The advantage of the crank-and-gear system is the combination of high load capacity, mechanical advantage, controlled movement, and height adjustment while supporting weight.

High Gear vs. Low Gear

Mechanical advantage also explains why most conventional commercial landing gear has two operating speeds: high gear and low gear.

The easiest way to understand them is:

High gear trades lifting power for speed. Low gear trades speed for lifting power.

High Gear — Moving the Legs Quickly

High gear is primarily used when little or no trailer weight is resting on the landing gear.

Each crank rotation produces more landing-leg travel, allowing the operator to extend or retract the legs relatively quickly. During uncoupling, for example, high gear can be used to move the landing gear from its retracted position down toward the ground.

But there's an important limitation:

High gear is not intended for lifting a heavily loaded trailer.

Think of high gear as the travel gear. Its job is to cover distance quickly when significant lifting force isn't required.

Low Gear — Moving Weight

Once the landing gear reaches the ground and begins supporting significant trailer weight, low gear becomes important. Low gear changes the gear ratio so the landing legs move a much smaller distance with each crank rotation. The operator therefore has to turn the crank more times—but gains substantially greater mechanical advantage. A bicycle provides a useful comparison.

When climbing a steep hill, shifting into a lower gear means you have to pedal more times to cover the same distance, but each pedal stroke becomes easier.

Trailer landing gear follows a similar principle:

More rotations. Less force required per rotation. Greater ability to move weight.

Industry Fact: The Difference Can Be Hundreds of Rotations

Manufacturer specifications show just how dramatic the difference between high and low gear can be. For example, SAF-Holland lists its HOLLAND Classic landing gear at approximately:

High Gear — 3.2 crank turns per inch of travelLow Gear — 19.3 crank turns per inch of travel

Over 10 inches of landing gear movement, that works out to approximately:

32 crank rotations in high gear

versus

193 crank rotations in low gear

Another SAF-Holland system, the HOLLAND ATLAS 55, is listed at approximately:

High Gear — 4.5 turns per inchLow Gear — 38.7 turns per inch

Over the same 10 inches:

45 rotations in high gear

versus

387 rotations in low gear

That's a difference of 342 additional crank rotations over only 10 inches of travel.

The exact numbers vary considerably by landing gear manufacturer, model, gear ratio, and application, but the engineering principle remains the same:

High gear provides more travel per rotation. Low gear provides greater mechanical advantage.

That tradeoff is what allows the same landing gear system to move quickly when unloaded and still provide the leverage necessary when substantial trailer weight must be controlled.

Why Not Just Use Low Gear All the Time?

You could move the landing gear through much of its travel in low gear, but doing so when the legs aren't supporting weight would create a lot of unnecessary work. Imagine making nearly 200 crank rotations when approximately 30 could accomplish the same unloaded movement. That's why a typical uncoupling sequence uses both gears.

High gear: Move the landing gear quickly toward the ground.

Ground contact: The feet or sand shoes reach the supporting surface.

Low gear: Use the increased mechanical advantage when trailer weight must be supported or trailer height adjusted.

When coupling the trailer again, the basic process reverses. Low gear is used while significant weight remains on the landing gear. Once the tractor is supporting the trailer and the landing gear is unloaded, high gear allows the legs to be retracted much faster.

⚠️ Safety Tip: Treat the Gearbox Like a Gearbox

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  The gears on the inside of landing gear - TurnNBurn adapter

High and low gear aren't simply two crank speeds. The operator is physically changing the mechanical relationship inside the landing gear gearbox.

Never attempt to change between high and low gear while actively rotating the crank.

Stop cranking before changing gears and follow the operating procedure specified by the landing gear manufacturer. Operators should also avoid using high gear when substantial trailer weight is resting on the landing gear. Low gear exists specifically to provide the additional mechanical advantage needed for loaded operation.

Simple Engineering Doing Serious Work

Trailer landing gear is a good example of how basic mechanical principles can accomplish an enormous amount of work. The operator supplies rotational force at the crank.

That force travels through the:

Crank Handle → Input Shaft → Gearbox → Internal Lifting Mechanism → Landing Gear Legs

On dual-leg systems, the cross shaft allows that motion to be transferred to the opposite leg so both sides operate together. The gearbox then gives the operator a choice between two priorities:

Speed when the landing gear is unloaded.

Mechanical advantage when the landing gear is supporting weight.

The result is a system that can support a commercial trailer, adjust its height, and repeat the process thousands of times throughout the trailer's working life. And that's why those two steel legs underneath the front of a semi-trailer are much more than simple supports.

They're mechanical lifting systems.