The Importance of Tire Pressure Monitoring: a Firefighter’s Perspective

Jason Estep

Responding to and from incidents has traditionally been a leading cause of firefighter fatalities and injuries. It is an area that requires constant attention and improvement. Think about the changes we’ve seen in apparatus safety during the past 20 years. We have enclosed cabs, added reflective striping on all sides of apparatus, installed seat belt monitors and signed seat belt pledges, installed tire pressure monitors, and removed loose items from the cab-yet we are still having the accidents. Why? I think the answer is two parts: first is driver training. We have to make sure that the people driving these rigs are properly trained to handle the apparatus. I could write for hours on driver training, but we’ll leave that for another time. The second part of the answer is tire maintenance, or the lack thereof. Tires are an overlooked maintenance item and are more than likely a contributing factor to apparatus incidents, although it is often overlooked by investigators.

As firefighters, we take great pride in our equipment, always making sure that it is ready to respond at a minute’s notice. However, we often overlook the most important part of the apparatus-the tires. I know they’re black and round; we kick them to make sure they have air, and we usually spray tire shine on them for a parade. How much more do we need to know about a tire? We could all stand to gain a little more tire knowledge. Basic tire maintenance only takes a few minutes and is actually very simple, but it is important to understand the purpose, use, and limitations of a tire to properly maintain it.

Tire Construction

First, we need to understand how a tire is constructed. A radial tire is made up of six main parts: the inner liner, carcass ply, beads, sidewall, crown plies (belts), and tread. The inner liner is the tire’s air chamber, making tubes a thing of the past. Usually made of a synthetic rubber called butyl rubber, it is nearly impenetrable by air and water. However, over time it can allow for slight air loss, so make sure you check your tire pressures. The carcass ply is the layer above the inner liner, often made of textile cords or steel wire (or cables) bonded into the rubber. These cables are largely responsible for determining the strength of the tire. The bead is the area of the tire that seals to the rim. The sidewall protects the side of the tire from impacts with curbs, rocks, and other road hazards. This is also the area that important tire details can be found such as tire width and speed rating. The crown plies or belts provide a rigid base for the tread and serve as protection for the carcass ply and inner liner. Traction, propulsion, braking, and cornering are all provided by the tread of the tire, which is designed to resist wear, abrasion, and heat.

Multifunctional Parts

Tires are one of the most, if not the most, critical components on a fire apparatus. Most parts of a fire truck perform one function. Tires on the other hand have numerous functions that are vital to safe responses. The tire’s first job is to support the weight of the apparatus. Did you know that gross vehicle weight rating (GVWR) depends on properly inflated tires? A pressure loss of just five pounds per square inch (psi) in front tires can often be enough to lower the weight- carrying capacity of the tire below the weight capacity of the front axle.

The tire also acts as part of the suspension, softening the impact from the road. Tires that are below the recommended tire pressure can severely affect the handling of the apparatus, especially when dropped off the road or on rough roads. Tires transmit propulsion and braking power to the road, and they are a critical piece of the steering system. Tires that are underinflated have longer stopping distances than tires with the correct air pressure. This is very important considering fire apparatus already have a stopping distance nearly twice that of a passenger car. Your chances of hydroplaning also increase as your tire pressure decreases.

Tire Pressure

Did you notice that air pressure is critical in all the functions of the tire? Think of the tire as nothing more than a container for the air pressure. The air pressure is what carries the load, provides the spring rate of the tire, and shapes the tread for proper traction. It may sound obvious, but it is a critical point to understand. If you take the pressure in a tire with 100 psi in it while on the ground and then raise it off the ground with a jack and recheck the pressure, you’ll find that it still has 100 psi. How can that be?

A tire is somewhat flexible, like a balloon. When it is loaded against the ground, the flexibility of the tire keeps the air pressure constant. In other words, the shape of the container changes but not the pressure. This is why we have to increase the tire pressure as the load increases. Think of a balloon with one book on it. Now take a balloon of identical shape and size and put two books on it. If you did this on a glass table and you could crawl under and look up, you would see that the area of the balloons flattened against the table is different. It should not surprise you that the balloon with two books on it has the bigger footprint. It is also more flattened, or squashed. This is why it is important to increase tire pressure when you increase load. A tire is always going from a squashed or loaded shape on the bottom to an unsquashed or unloaded shape on the top. The bigger the difference between loaded and unloaded, or the more the tire squashes as it comes around, the more flexing that takes place, which generates heat.

Heat is the biggest problem to tires. In fact, more tires probably are damaged by heat than by road hazards. Also, the more the tire is flexing the less stable the vehicle is. This is often what is happening when a vehicle is described as “road walking.” When the proper inflation pressure is used, the tire flexes less, generating less damaging heat and providing a much more stable vehicle.

Additionally, operating apparatus with properly inflated tires contributes significantly to fuel savings.

Overinflation

What happens if you overinflate your tires? First, they lose their ability to cushion the load against road shocks. Second, tires have a maximum usable pressure and a particular load that they can handle at that pressure. Do not exceed the pressure or load of a tire. If you need to increase because of load, consult your tire dealer to select a tire that is suitable for the higher pressure. Third, the amount of inflation in tires also affects the footprint, size, and shape of the tires, which is critical to traction and wear. You would think that a bigger “footprint” would increase traction, but that is not necessarily the case.

Think of baseball spikes vs. a tennis shoe on soft ground. The set of baseball spikes will dig deeper than the tennis shoe because the load is distributed over such a small area. Now, if you are on a smooth, hard floor, you would be less likely to slip with the tennis shoe than the spikes. If there’s just a thin layer of wet or slick material, a higher inflation pressure and smaller footprint may help the tread bite through and get traction. On the other hand, on a thick, soft surface such as deep mud and sand, a lower inflation tire can distribute pressure over a larger area, so that the tire almost “floats” like a snowshoe.

Tire Management

What is the most important part of tire maintenance? If you didn’t answer air pressure, you may want to reread the past few paragraphs. Proper air pressure makes the tire do its job efficiently and safely. You can get a tremendous benefit with little effort just by managing your tires. We put a lot of effort, time, and money into making firefighting as safe as possible with a multitude of programs, slogans, classes, and products leading the charge-all of which are worthwhile. We are always asking for grants, funding increases, and so on to pay for these items. Wouldn’t it be nice to manage a multitude of safety factors for a minimal cost with little time investment? A tire management program is it.

As mentioned earlier, tires play a part in carrying the weight of the apparatus, vehicle stability, traction, steering, and braking distances. We are all very aware that these attributes are contributing factors to fire apparatus accidents. A proper tire management program can significantly reduce these risks.

So what is a tire management program? It is a very simple program that puts a premium on proper tire pressure management, along with the condition of the tires and tread depth.

National Fire Protection Association (NFPA) 1901, Standard for Automotive Fire Apparatus, (2009 ed.) requires adding visual indicators or monitoring systems that monitor each individual tire’s pressure on all new apparatus. Tire pressure monitoring systems (TPMS) are wireless systems that monitor each individual tire’s pressure and temperature. Most of this information is reported in the cab of the apparatus, which requires constant checking to see if you have a low tire. Although this is a step in the right direction, it still requires a good bit of effort in checking, and often you may not know that a tire is low until you are ready to respond.

What if there was a system that allowed you to only deal with the exceptions? In other words, wouldn’t it be great if we could just concentrate our time and effort on the tires in the fleet that have tire pressure faults? How about being able to review the tire pressures across your entire fleet at a moment’s notice? What if you had an alert e-mailed or text messaged directly to you and your officers, drivers, and so on any time a tire had a pressure fault?

One such system is the FireSyte monitoring system that allows fleet managers to monitor tires real time, any time. You can set up alert bands for any tire position on any apparatus, customizing them for each individual truck. Once the alert bands are broken, an alert will be e-mailed or texted directly to the designated users. A fleet report can also be sent at a preset interval (daily, weekly, and so on), which will give you verification that all tires are being monitored and that the pressures are within spec. This system is very simple and easy to install.

The fire service continues to face staffing and budget shortages. We have to find ways of working smarter to accomplish the same tasks that we have performed in the past, and these types of systems can help us achieve that goal. I also see them as game changers in apparatus safety and the fire service’s goal of eliminating firefighter fatalities.

JASON ESTEP is a firefighter with the Morrisvale (WV) Fire Department. He has a degree in mechanical engineering from Fairmont State University.

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