Best Practices for Safe Tipping: What Drivers and Operators Can Do

At STAS, safety isn’t just a feature—it’s the foundation of everything we build.
Tipping a fully loaded trailer involves complex mechanics, and even small misjudgments can lead to dangerous situations. That’s why we focus not only on designing safe trailers but also on sharing clear, practical tips to help operators stay safe in the field.

Quick recap: the physics of safe tipping

From a physics perspective, safe tipping comes down to two principles:

• The ground must be as level as possible

• The center of gravity must be as low as possible

Let’s break down how operators can manage both factors in practice.

1. Keeping everything level

Ground surface

It’s not enough for the surface to look level—it also needs to be solid. When tipping, axle loads increase briefly, which means the ground must support that extra weight. Even compact ground can become unsafe when wet.

If the surface looks loose or soggy, don’t tip there—even if it’s safe to drive on.

The trailer

Stability depends on more than just the ground. Between the load’s center of gravity and the ground are:

• The body

• Tipping hinges and cylinder trunnions

• The chassis

• The suspension system

• The tires

If any of these components are worn, damaged, or misaligned, they reduce the trailer’s stability. Key maintenance checks include:

• Tires – Check air pressure and damage, especially on the last axle if air bellows are deflated during tipping

• Suspension – Inspect rubber bushings and axle bodies

• Chassis and body – Clean regularly; damage is easier to detect on clean surfaces

The truck

The trailer’s front end is supported by the truck. If the truck and trailer aren’t properly aligned, uneven load distribution occurs at the cylinder hinge—one of the most critical structural points.

Always ensure all wheels are straight and the trailer is in line with the truck before tipping.

Load distribution

Uneven loading shifts the center of gravity to one side—something to avoid at all costs. Be extra careful when:

• Loading with a bulldozer from the side

• The loading operator cannot see inside the body

• Using automatic sheeting systems—check the load before closing the cover

Key tips for level tipping:

• Only tip on level, solid surfaces

• Regularly inspect and maintain the trailer

• Evenly distribute the load inside the body

• Keep truck and trailer perfectly aligned

• Watch out for strong winds, which can affect trailer stability

2. Keeping the center of gravity low

The lower the center of gravity, the lower the risk.

The required tipping angle depends on two factors:

1. How easily the load slides on itself (angle of repose)

2. How easily the load slides over the trailer floor (friction)

1. Angle of repose

This is the steepest angle at which material can pile up without collapsing. The lower the angle of repose, the better the flowability, and the sooner the load will begin sliding.

• Dry, granular materials (e.g. grain) have a low angle of repose—safer

• Moist or sticky materials (e.g. wet sand) require a steeper angle—less safe

2. Friction against the floor

Friction is the resistance between the load and the trailer floor. Moisture increases friction—meaning the load sticks more and needs a steeper tipping angle.

For example:

• Dry chalk flows easily

• Wet chalk sticks and clumps

Also consider cold weather: moist loads can freeze to the trailer body, dramatically increasing tipping risks.

Air suspension: inflate or deflate?

It’s long been considered best practice to deflate air suspension during tipping. That’s why most STAS tippers include an automatic deflation system.

Deflating has two major advantages:

• Lowers the center of gravity

• Removes the "air cushion" for more stability

However, deflating also means the weight is no longer evenly distributed across the three axles. In our tests, the rear axle’s load jumped from 8 to nearly 20 tonnes.

So while deflation is safe on solid ground, it can be dangerous on undeveloped or soft surfaces.

Our recommendation:

Only tip on developed, level surfaces—regardless of air suspension settings.

Final checklist for drivers & operators

Before the day starts:

• Check tires for damage and ensure 9 bar pressure

• Inspect suspension components—especially rubber bushings and axle bodies

• Assess trailer maintenance status

While loading:

• Observe the angle of repose (how the load stacks)

• Check for moisture or abrasiveness

• Make sure the load is evenly spread

While driving:

• Monitor rain: moisture increases friction

• Be mindful of freezing temperatures: loads can stick to the body

• Factor in wind speed, especially with high sidewalls

Before tipping:

• Confirm the ground is flat and stable

• Ensure truck and trailer are straight

• On soft or uneven ground: consider inflating the air bellows