Best practices for safe tipping

At STAS, safety isn't just a feature—it's a fundamental part of our engineering philosophy. We know that tipping a fully loaded trailer involves complex mechanics, and the stakes are high for drivers, operators, and fleet managers alike.
Our commitment to operational safety focuses on two key areas:
1. Maximizing Safety Margins: Through rigorous engineering, high-quality materials, and optimized manufacturing, we ensure our trailers are safe under all conditions.
2. Educating Operators: By sharing insights and best practices, we help ensure trailers are used safely and effectively.
Safety is not just a checkbox; it's a continuous challenge and a shared mission between STAS and our end users.
This blogpost is the second in a series of blogposts about tipping safety and tipping trailer stability. We are now shining a light on what drivers and operator can do to maximize the safety margin during tipping. It's recommended to read the first blogpost in the series before reading this one because the first blogposts lays the foundation for the information given here.
Click here to navigate to the other blogposts in this series:
The physics of tipping trailers
How we redefine tipping trailer safety

So, let’s zoom in on both and go over the things that can be done to maximize safety.
Keeping everything level
This seems easy at first glance: just tip only on perfectly level ground and in theory, nothing can go wrong. Unfortunateley there are some variables at play that are not always obvious.
Ground surface
The ground surface underneath a tipping trailer needs to be flat to begin with. When tipping, the weight on the trailer’s wheels increases for a short time, so the ground must also be solid enough to handle this. It’s important to remember that even solid-looking surfaces can quickly become soft and unsafe when they get wet. (See "The best air suspension settings for tipping" below for more information.)
If a ground surface seems loose or not compacted enough, it’s probably unsafe to tip, even if driving on that surface is still possible.

The trailer
The ground isn't the only thing supporting the weight when tipping. Between the trailer's center of gravity and the ground there are several important parts, including:
- The body
- The tipping hinges and cylinder trunnions
- The chassis (frame)
- The suspension system
- The tires
All of these parts work together to support the trailer and if any of these parts are worn, damaged, or asymmetrical in any way, they make the trailer less stable and safe.
To keep the trailer as safe as possible, it’s essential to perform regular maintenance and visual inspections. The following trailer parts are the most important to keep in mind:
- The tires, checking for proper air pressure and damage, paying special attention to the tires on the last axle if you deflate the air bellows during tipping.
- The suspension, especially the rubber bushings and axle bodies. Again paying special attention to the last axle if you deflate the air bellows during tipping.
- The overall condition of the chassis and body, it's a good idea to do this inspection when you're cleaning the trailer. Cleaning is a good opportunity to go over every inch of the trailer and damage is usually more visible on clean surfaces.
Regular checks can help prevent issues and keep the trailer safe during tipping, especially on the last axle where the applied forces can increase dramatically during the tipping process.

The truck
The front of the trailer is fully supported by the truck, so the truck plays an important role in keeping the trailer stable while tipping. It’s very important that the truck and trailer are lined up correctly.
If the truck and trailer are at an angle relative to each other, there's asymetrical deformation in the front end of the chassis because the fifth wheel can only rotate around one axis relative to the truck. This means that the weight pushing down on the tipping cylinder will push one front corner of the chassis further down than the other, which introduces asymetrical load on one of the most important structural parts of your tipper: the cyclinder hinges.
For safe tipping, make sure the truck and trailer are perfectly aligned, with all wheels pointing straight. This increases overall stability and prevents accidents.

Load distribution
Make sure that the load is evenly distributed in the body at the time of loading. Having more load on one side than the other shifts the center of gravity by default and of course, this is something that must be avoided at all times. Pay special attention to the loading process when the trailer is loaded by means of a bulldozer and when the loading machine operator cannot see inside the body.

Conclusions on how to keep your tipper level
To keep the trailer stable and safe while tipping, remember these key points:
- Check that the ground is level and solid before unloading.
- Regularly maintain the trailer and inspect all parts that carry weight.
- Make sure the load is evenly distributed when loading.
- Keep truck and trailer as straight as possible during tipping.
- Be aware that high winds can also reduce your safety margin.
Keeping the center of gravity low
The lower the tipping angle needed to unload, the safer the situation is.
The tipping angle needed depends on the type of load. Two main factors affect this:
- How easily the load slides off itself
- How easily the load slides down the trailer floor
The required tipping angle is the angle at which the load begins to slide off itself or down the trailer floor, depending on which happens first.
How easily the load slides off itself
The correct scientific term for this material property comes from the bulk shipping sector and is called “angle of repose”. It describes the steepest angle at which a material can pile up without sliding. The angle of repose is very closely linked to the “flowability” of the load and therefore the tipping angle needed for the load to fall out if it doesn’t slide down the trailer floor. The lower the angle of repose, the better the "flowability" of the material.

A lower angle of repose is safer. Figuring out the exact angle requires scientific testing, so we won’t go into that, but here’s what we know from research:
The angle of repose depends mostly on how rough the particles are and how much moisture the load contains.
For example, dry grain has a lower angle of repose than wet sand, meaning it’s easier to unload.
How well the load slides off the body floor
This is again a material characteristic that is well-described scientifically, called friction.
Friction is how much two contacting materials oppose movement relative to each other, in our case the bulk load and the aluminium or steel of the tipper body. More friction means that higher forces are needed to get the load to move, or in other words, a higher tipping angle is needed.
Calculating the exact friction between the body and a certain load would again be too complex to do on-the-spot, but it’s useful to know that moisture content does matter again.
Think about how dry chalk behaves compared to wet chalk. Also note that freezing outside temperatures can make moist load types freeze to the body, which is bad news for safe tipping.

Conclusions on how to keep the center of gravity low
How steep you need the body to tip before the load starts to discharge is very dependent on the characteristics of the specific load that’s transported.
However, there are a lot of cues drivers can use to gain insight in these variables before tipping, and most of these checks can be done on-site where the loading happens.
If it’s possible, take a good look at the heaps that are on-site when loading. This will give you an idea of the angle of repose.
If the load type allows it, it can also be a good idea to grab some of the load in your hand to guesstimate the friction between load and body, and to get an idea about how steep the angle of repose could be. If the load falls through your fingers, the load is dry and you’re probably fine. If you can make a ball with the load, the load is moist and you’re at risk.
In summary: The ultimate checklist for drivers and operators
Of course, on-site safety rules are there for a reason and should always be obeyed first and foremost. However, these rules usually only cover on-site safety and do not mention the best practices we see from our perspective as a tipping trailer manufacturer.
Tipping safety may seem very simple at first, but a lot of variables are important and the cases we have seen in the past never have a one-mistake explanation. It's always a sum of issues that creates unsafe situations. Making sure everyone involved has a good idea on what to out look for is probably the best thing we can all do to avoid unneccesary accidents and damage.
Based on all of the above information, we can extract a practical checklist for drivers and operators that greatly improves on-site safety. We have broken down this list of topics based on the logical steps most drivers will be confronted with:
Checks before starting your day:
- Trailer tire damage and tire pressure;
- Focus on the tires of the last axle if you deflate the air bellows during tipping.
- Check that tires pressures are all at 9 bar and do not tip with damaged tires.
- Trailer suspension condition;
- Focus on the suspension of the last axle if you deflate the air bellows during tipping.
- Visually check the bushings, air bellows and axle bodies.
- Trailer maintenance level.
- When in doubt, ask your local STAS dealership.
Checks while loading
- Angle of repose of the load;
- If you have the chance, look at the angle of the heap.
- The lower the angle to the ground, the better.
- Friction between load and body;
- If the load is moist and made out of small abbrasive particles, keep this in mind during unloading.
- Load distribution inside the body.
- Make sure to take a look inside the body before you close the sheet if you have automatic sheeting.
- Take special care when the trailer is getting loaded from the side with a bulldozer.
Checks while driving
- Rain;
- Keep in mind that moisture content can change the friction properties of most loads.
- Is your sheeting watertight?
- Outside temperature;
- Is it freezing? loads with high moisture contents can freeze to the inside of the body.
- Wind speed.
- The sidewalls are a pretty big surface for the wind to push against. Don't underestimate wind force.
Checks before unloading
- Ground surface underneath the trailer;
- Is the ground surface underneath the trailer flat and level? If not, don't unload in that spot.
- Is the ground surface stable enough to support the higher axle loads while tipping?
- When in doubt, don't unload in that spot.
- when tipping on compact gravel or on building sites, it's advisable to inflate the bellows to keep the weight on the axles distributed.
- Are all truck and trailer axles in a straight line?
- If not, change your position.
This blogpost is all about what drivers and operators can do to increase the safety margin when tipping, and a big part of that is about the condition of the trailer that’s used. Of course, as a manufacturer of tipping trailers, we have a responsibility to maximize safety by design in every tipper we manufacture.
Click here to read all about why a STAS tipper is the most stable tipping trailer available.
Or click here to read all about the physics behind tipping a tipping trailer.