TRUCK DRIVERS should know and understand their aerial device and how it functions. Of course, on its face, this isn’t a big ask—most drivers love to talk about the aerial. After all, it’s the flashy part of the rig. But to really call oneself an expert is to know that your aerial operations are only as good as their foundation: the stabilizers. They are small compared to much of the truck’s equipment and tiny compared to the aerial or bucket, so they are often overlooked. Still, don’t let their size fool you; they’re a critical component of aerial operations.
We’re going to tackle aspects of your stabilizers that will help you feel like the master driver you are. And don’t worry if you are new to this. To understand the advanced concepts, we need to be confident in the basics. And to feel confident in the basics, we need to be fluent in stabilizer terminology.
Surface Area and Pressure
Let’s start by covering the underlying principles at the core of stabilizer use. Surface area and pressure are, hands down, the most important concepts to grasp when we talk about stabilizers. If you don’t know what your stabilizers are doing to the ground, operating them becomes a guessing game. The last thing we want to do is guess and guess wrong. If we understand pressure, we can instead accomplish more advanced operations from a place of knowledge.
A good starting point when we look at surface area and pressure is to look at your tires and how they interact with the surface they sit on. First, take the imprint of your tires. Think of this like a footprint: It is the area where your tire touches the ground while it sits, motionless. Measure the length and width of this imprint. The front and rear tires can be different sizes, so it’s important to check out all your tires. These measurements do not need to be exact; we are simply working toward a rough estimate that will help us make quick judgment calls in the future.
Once you get the measurement, multiply the length and width. Do this for all the tires and add them all together. Next, you need to know the weight of your vehicle. You can use the gross vehicle weight rating listed in the cab or, hopefully, you have weighed your truck and know your in-service weight. Either weight will work for this exercise. Once you have that number, divide the weight by the surface area of all your tires to find the pounds per square inch (psi). This is the force your vehicle exerts on the ground.
1. Extended stabilizer penetration on the front stabilizers is used to increase the aerial scrub area off the rear of the truck. (Photos by author unless otherwise noted.)
2. This truck’s auto level was used to overcome this steep topography. The rear of the truck is high off the ground, making it difficult to access equipment. With the truck’s height and the length of the access ladder, reaching the turntable will be difficult. [Photo courtesy of Arlington County (VA) Fire Department Tower 104 “A” shift.]
I ride on Tower 104 at work. It weighs 80,800 pounds. Throughout this article, I’ll use this vehicle to demonstrate psi and related concepts. The tires on Tower 104 cover a surface area of approximately 15 inches x 13 inches on the front tires, and there are two of them (15 x 13 x 2 = 390). The tires on the rear cover a surface area of approximately 11 inches x 10 inches, and there are eight of them (11 x 10 x 8 = 880). We can add them together to get the total square inches of Tower 104’s tires covering the ground (390 + 880 = 1,270). Remember, it’s OK to use ballpark numbers. Then divide 80,800 pounds x 1,270 square inches to get approximately 64 psi.
Now that we have our truck’s psi, consider how the calculation compares to the guidelines outlined under National Fire Protection Association (NFPA) 1900, Standard for Aircraft Rescue and Firefighting Vehicles, Automotive Fire Apparatus, Wildland Fire Apparatus, and Automotive Ambulances. There was recently a change to the standard as it relates to stabilizers, but it helps to startwith the earlier guidelines that a veteran driver might be more familiar with. Prior to 2024, NFPA 1900 required stabilizers on aerial apparatus to exert less than 75 psi from each stabilizer on the ground. This is not a number you need to memorize but rather a number to apply to the Tower 104 example. In that scenario, the tires each exerted 64 psi on the ground. 64 psi is less than the 75-psi maximum exerted by each stabilizer.
This concept can help us understand that if you drive over a surface you are unsure of and it holds the vehicle, there’s a good chance it will also hold the stabilizer when deployed. But if your vehicle sinks as you drive, there’s a high likelihood the surface will not hold your stabilizer. At this point, we are working with chances and likelihoods, which is why rough estimates on psi for the aforementioned equation are acceptable. This information allows you to make informed choices as you arrive on the scene.
Now, let’s tackle the updated standard. It’s a subtle change, but as of 2024, NFPA 1900 increased the allowable psi from 75 to 100 for each stabilizer. This can affect the stabilizer pad’s size (surface area) or allow for increased tip loads on the aerial device. This will not change aerial devices and stabilizers overnight, since the manufacturers would need to reengineer each device. But it’s nonetheless an important update. Later, we’ll cover how you can reduce, or even inadvertently increase, the psi exerted on the ground by your truck.
Stabilizer Lingo
A review of basic concepts and lingo is necessary before we examine stabilizers in depth. You may be aware that there are a couple of styles of stabilizers, but the concepts remain the same. First, the distance the stabilizer can extend down into the ground is called stabilizer penetration. In the past, stabilizer travel or penetration was lacking. Stabilizers were designed to make ground contactnothing more. Ground contact is when stabilizer is loaded but does not lift the truck off the ground or suspension. More recently, trucks have been given additional stabilizer penetration as a standard option, and there are typically options to increase your stabilizer penetration when specifying a new truck.
Under the stabilizer is the stabilizer pad. The stabilizer pad can be made of metal or poly material. The size of the stabilizer pad can vary by truck and even by stabilizer. Some manufacturers are incorporating the stabilizer pad into the stabilizer design. This eliminates the need to store or deploy a pad separate from the stabilizer. The stabilizer pad needs to be placed where the stabilizer will land.
There are three standard setups when it comes to stabilizer placement:
- Fully jacked—all the stabilizers are fully extended away from the truck and have made ground contact.
- Short-jacked—one side fully extends away from the truck and makes ground contact. The other side can be extended away from the truck but stops short of full horizontal extension. The stabilizer still makes ground contact. The aerial will have limitations on the short-jacked side. Depending on the truck, it might fully limit where you can operate on the short-jacked side, or it may limit the reach or the tip load of the aerial device.
- No-jacked—both sides are short-jacked. Not all trucks can short-jack, and not all trucks can no-jack. A no-jacked truck has all its stabilizers make ground contact but is limited in horizontal extension on both sides of the truck. This would limit the aerial operation directly in line with the vehicle with three to five degrees of side-to-side operation.
Deployment
Once you have placed the stabilizer pads in the correct location, you can deploy the stabilizers and look for ground contact. As the stabilizer makes ground contact, some trucks will automatically level. The auto-level feature is great for normal operations and decreases the time it takes to set the truck up. It works by extending the stabilizers vertically to level the truck front to back and side to side. One limitation of the auto-level is that the stabilizers only deploy down, and it works to accomplish “exact” level. This can extend the stabilizer and raise the truck high off the ground.
3. The aerial is deployed off the officer’s (right) side of the truck, and the stabilizers on the driver’s (left) side of the truck are floating. This is acceptable and is outlined in the truck’s operator’s manual.
4. A less common issue is ground contact when it comes to surface area. This road is in bad shape and has spots where the stabilizer pad does not make contact, increasing the pressure on the other parts of the road.
How far you extend the stabilizers ultimately affects the reachability of the equipment on the truck. Having the extra ground penetration on the stabilizers is a great tool for overcoming obscure topography. Unfortunately, you might set your truck up so high that equipment is out of reach for most firefighters. But, without it, things like a crown in the road can limit your ability to level the truck and lift it off the suspension.
There are downsides to leaving the tires on the ground and, more specifically, extending the stabilizer vertically just enough to make ground contact. This leaves the apparatus on the suspension and allows the suspension to have a say in your operations. The suspension will f lex when loaded, and it can cause the stabilizer on the nonoperational side to come off the ground. This is called floating an stabilizer.
Cranes, when lifting heavy loads, will also experience this condition. Crane operators know and understand the circumstances under which this is allowable. As the operator, you need to investigate and understand if floating an stabilizer is acceptable. This information should come from the manufacturer.
It’s important for drivers to find out this information and educate the leaders in the organization. The last thing a competent operator wants is an officer shutting down a safe and acceptable operation due to a lack of knowledge. It’s up to you as the operator to bridge that gap.
Start by looking in the operator’s manual. This document came with the truck from the manufacturer and should contain most of the information you need to tackle the ins and outs of your stabilizers. Some manufacturers test and allow for stabilizers to float. Some do not allow or account for it, which makes a big difference in your decision making. If you want to prevent floating, lift the truck off the suspension, operate the aerial in line with the truck (front or back), or keep the aerial at a higher operating angle above 45°.
As with any operation, there are limitations to account for when you lift the tires off the ground and take the suspension out of play. Your aerial will be impacted when the tires are off the ground. Some devices limit your extension over the front of the cab when the front tires are lifted. But when the rear tires are off the ground, there is usually no limitation on your aerial; instead, there’s a limitation on your braking and surface area or psi. These factors are important considerations in your setup process.
When you choose to keep the front tires on the ground and lift the rear tires off the ground, you need to ensure the front wheel lock is engaged or that there is a braking system on the front axle. If icy or slippery conditions exist, consider positioning the vehicle so the rear tires stay on the ground. This will add more surface area and more braking power to help prevent the truck from sliding. Keeping the rear or all tires on the ground also helps to increase surface area and reduce the psi exerted on the ground.
You can use cribbing or cribbing-like material to increase the surface area of the stabilizer pad. Use cribbing in conjunction with keeping the tires on the ground or to help offset the tires being off the ground. Departments will use 4 × 4 cribbing or ¾-inch plywood pads to expand the stabilizer footprint. Think about placing this material below your stabilizer pads when on an unpaved or not-as-stable surface. At this point, you’d need to know the size of the stabilizer pad.
Tower 104 has 31-inch x 26-inch stabilizer pads. The stabilizer pad surface area is 806 square inches (31 x 26 = 806). Remember, this can change for each truck and even each stabilizer on the same truck.
Tower 104 has a compartment depth of 20 inches, which is how long its 4 x 4 cribbing is. Increasing the surface area would require 14 4- x 4- x 20-inch pieces of cribbing. This is per stabilizer pad and stabilizer. Tower 104 has four stabilizers, requiring 56 pieces of cribbing to increase the surface area of all four stabilizers properly. The chances of using cribbing on all four stabilizers simultaneously are very low. This information just highlights knowing what your truck can or can’t do based on how you equip it. Another option would be to carry 3⁄4-inch plywood pads since they can take up less space and accomplish the same mission. The important thing is to understand what is needed and equip the truck appropriately to accomplish advanced operations.
When setting stabilizers, one of the more common problems is encountering a curb or some sort of topography change. This would be a vertical application of cribbing. Remember, when using wood or any cribbing, you must cover the same or greater square inch surface as your stabilizer pad. Using cribbing to level out your stabilizer or overcome a curb does not mean the footprint should shrink. Let me repeat that: You should not shrink your footprint and increase the pressure being exerted on the ground. I have seen many pictures where cribbing is used and instead of covering the surface area under the stabilizer pad, it covers only two- thirds of it. That is a huge increase in pressure on the ground. Like anything else in the fire service or life, it is OK to do it if you know you are doing it and you know how it will affect your operation. But in nearly all cases, you do not want to increase stabilizer psi when you can just as easily come prepared with enough cribbing for these situations.
For instance, if I were to use eight 4 x 4 pieces of cribbing with a length of 20 inches each, they have a combined surface area of 540 square inches. My ground pad covers 806 square inches. The reduction of the surface area changes my pressure from 75 psi with my stabilizer pad to 112 psi using the eight pieces of cribbing. Now, if this is done on a substantial concrete sidewalk or driveway, it is probably not an issue. However, the situation changes if this is to bridge a curb into a grassy area. Using 14 pieces of 4- x 4- x 20-inch cribbing increases the surface area to 940 square inches and drops the psi to 64. The relation of cribbing to the stabilizer pad is shown in photos 5 and 6.
5 & 6. Here’s a visual of what eight pieces of cribbing look like and the surface area they cover of the ground pad compared to 14 pieces. Eight pieces of cribbing leave parts of the ground pad uncovered, decreasing the surface area and increasing the pressure on the ground.
So, again, return to the operator’s manual. You must ensure you read and follow it when you use cribbing. If the manual states you need hardwood material for cribbing, not softwoods like pine, you must place hardwood cribbing on your truck.
For any operation in which you place cribbing under the stabilizer, the driver is the individual who is liable for not using the wood specified in your truck operator’s manual. Cribbing up the stabilizer pad requires reading the operator’s manual, ensuring the vehicle carries the proper material, and properly training the driver/ operator in its use. This is accomplished by—you guessed it—reading the operator’s manual, understanding the basic stabilizer setups for your truck, and askingthe engineers who designed your aerial device-specific questions. Believe it or not, the operator’s manual contains information so specific to your aerial device that even an expert on aerial devices won’t be able to give you an answer on what your truck can and cannot do without reading it, too.
Take the stabilizer fundamentals, as well as the basic and advanced operation techniques outlined in this article, back to your department and explore them on your trucks. Use it to inform the purchase of any new or new-to-you truck. The days of one- size-fits-all aerial operation have come to an end. That’s not a bad thing. In fact, if you understand your device and all its components, even the stabilizers, you can enjoy the freedom that comes along with being confident in your truck operations.
NICK WILBUR is a firefighter/EMT for the Arlington County (VA) Fire Department and a captain in the College Park (MD) Fire Department. He writes for Fire Engineering and was a H.O.T. instructor at FDIC International for ladder placement. He works for EVR, conducting training and specification services.
