When I was a kid, like a lot of other little boys, I loved Hot Wheels. I would play with those little cars for hours, ramping them off stuff, making little motor noises, and sliding them around doing impossible turns. I remember one day coming downstairs and excitedly telling my dad that we should get wheels like Hot Wheels had. My dad’s pickup had suffered a blowout a few days before, and he was in a bad mood about it. I thought we could get solid plastic wheels, and solve the problem forever. After all, my Hot Wheels never got flat tires.
As an adult, I know that tires are a lot more complicated than a hard disk of plastic. When you start looking at that job in the context of a semi, it gets even more complicated. Tires designed for over-the-road trucking have very different needs than tires designed for short haul. For specialized trucks that are almost always off road, the challenges are even more complex, with all the needs of other trucks while also being able to withstand constantly rolling over debris. And that’s before you start considering the different needs of steer tires, trailer tires, and drive tires.
There are dozens of options for each application. For larger fleets, keeping up with tire maintenance and ordering can be a full-time job of its own. Tires are a complicated piece of engineering. But one thing all of these tires have in common is also the simplest thing to get right. Tires, all tires, work best when properly inflated.
Low Pressure Problems
If you think you can eyeball your tires, or use something like a tire-thumper, consider this. The American Trucking Association Technology and Maintenance Council sent a team out to check tire pressure across the industry. They stopped in on larger fleets. They checked owner-ops and smaller fleets and truck shows and truck stops. They found only 44% of trucks were within 5 PSI of the recommended pressure. 1 out of every 5 trucks they checked had one or more tires that were 20 PSI low. These are real numbers from working trucks.
Low tire pressure is a widespread problem, and the consequences can be severe. Under-inflated tires cost fleets money, they cost fleets time, and they put everyone on the road at risk. If you take nothing else from this article, take that with you. We’ll go into some more details here in a minute, but the bottom line is simple. You’ve got to maintain your tire pressure. Whether that means technological solutions, or getting down on the ground every morning with a pressure gauge, eyeballing it just won’t cut it.
How Much Money Does Under-Inflation Cost You?
The specific answer, of course, will vary from fleet to fleet. The more trucks you have, the more the problem will compound. Tires are typically the second largest expenditure for a trucking company. The biggest cost is fuel.
Running tires low destroys fuel economy. About 1/3 of a truck’s fuel consumption comes from overcoming the rolling resistance of its own tires. Allowing the tire to go below proper pressure increases that resistance. That, in turn, increases the fuel needed to overcome that resistance. How much of an increase? A tire that is 5PSI too low can see a 5% reduction in fuel economy.
The average semi gets 6.5 MPG. Real world numbers range between 4 and 8 depending on the equipment and the application, but let’s use the average for ease. A 5% reduction means the average truck is now getting 6.175MPG. Let’s take another general estimate of 100,000 miles driven a year. Some trucks will go much more than that, and some will go much less, but 100,000 puts us in the middle of the pack.
For a truck traveling 100,000 miles getting 6.5MPG, they’ll use 15,385 gallons of fuel. In 2018 diesel stayed around $3 a gallon. That puts our hypothetical average truck at $46,155 spent on fuel. With tires under-inflated by 5PSI, we would need 16,195 gallons of fuel to get that same distance. That means, to travel the same distance, our truck would have spent $48,585. That’s $2,430 spent on fuel because of under-inflated tires. How many trucks do you have?
But the costs don’t stop there. Running tires low reduces their useful life. With tires running around $500 each, and more fuel efficient or specialized tires running even more, you want to get as much life as possible out of them. The tread on a tire with low pressure experiences increased stress. The tire deforms and the interior of the tread rubs against itself. This makes the tread wear out faster, and without ever touching the road.
Even worse, tires running low for extended periods will experience damage to their sidewalls and core. This means that when the tread wears out prematurely, it is less likely you’ll be able to retread the tire. According to the tire manufacturer Michelin, truck tires are designed to be retreaded at least once. If maintained well, they can often take a third retread before they are beyond their useful life. Running under-inflated robs you of the full lifespan you paid for.
Adding insult to injury, recent research by Michelin America’s Research Group scientist Cesar Zarak found that in dual-tire setup’s where one is under-inflated, it is most often the properly inflated tire that fails first. The properly inflated tire is put under increased stress as it takes more weight than the under-inflated tire. This means that, when the tire fails under the stress, you lose a good tire, and a tire that has already had its lifespan shortened by under-inflation.
Of course, tire life isn’t the only financial consideration. Time management is always a huge concern, especially now, with hours under closer watch than ever. Proper tire inflation helps you avoid unexpected downtime, too.
What run would you like to postpone on the side of the road to get a tire replaced? Obviously, no one wants to stop the truck midway through a shipment. So why do so many people ignore tire maintenance and wait until they have to react to a tire emergency?
Proper inflation won’t make a tire last forever. Eventually, even the best maintained tire will need replaced. The difference is, a properly maintained tire will need to be replaced when its tread is completely gone. This is a predictable event that you can factor into the overall logistics of your fleet.
By contrast, under-inflated tires fail unexpectedly. Instead of scheduling the tire change, you’re doing roadside emergency replacements. Not only does this completely destroy whatever plan was in place, it costs more money too.
The Worst Things That Can Happen On The Road
So, when’s the best time to have a blow out? When’s the best time to lose control of a truck? When’s the best time to try to stop and find out you can’t?
Driving is the most dangerous thing most people will do in a normal day. And truck drivers do it every day, all day. There’s a reason truck driving is the 8th most dangerous job in the US. That’s more dangerous than being a fire-fighter or police officer.
The tire is the point where the driver’s skill interacts with the road. If that interaction point fails, even the most skillful driver will be hard pressed to maintain control. Improperly inflated tires increase the likelihood of that failure.
When a tire is under-inflated it fails to hold its shape. As the sidewalls sag under the weight of the load, the tread tilts inward, toward the center of the tire. These two factors compound each other. The sagging sidewall loses its structural integrity. The treads rub against each other, rather than the road, creating friction and heat that builds up in the tire.
As that heat builds up, the air in the tire expands and pushes on the already weakened sidewall. The faster the truck is moving, the more dangerous this situation gets. When the pressure exceeds what the sidewall can resist, the tire explodes.
Over-inflation creates the opposite problem. An overinflated tire loses its ability to flex with the bumps and bangs of imperfect road surfaces. This puts extra strain on the sidewalls. When the tire goes into a hole or over a bump, the pressure change can cause the tire to explode.
The other situation where under-inflation can create a safety risk is rain. Modern tires are designed to push and channel rain away from the center of the tire, allowing the wheel to grip the road. With the weight of a loaded semi pushing down on them, the tires do a good job of pushing that water out and away. But with under-inflated tires, the shape of the tread changes and can actually trap the water. This creates a bubble or wedge that the tire is continuously rolling up on. At slower speeds, this effect is negligible, but at highway speeds, it can build up to the point where the truck has minimal contact with the road. If a driver needs to stop abruptly in these conditions, they might find their truck sliding rather than stopping.
Improperly inflated tires cost you money, waste your time, and put you and everyone else on the road at risk. Unfortunately, most drivers don’t do a very good job of maintaining their tires. I think this is because checking all of them every day is a hassle. It takes too long and there is too much other stuff to do. With no obvious, immediate benefit, a lot of drivers skip tire pressure checks entirely.
A good tire-pressure monitoring system can eliminate the hassle of checking the tires. Some of the newer systems transmit tire pressure information back to a central database. This allows fleet managers and admins to monitor every tire in the fleet. That's a powerful accountability tool.
Whether you decide to go high-tech or low, maintaining proper tire pressure will pay dividends in the future. It’s a simple step to ensure your trucks are safe, on-time, and profitable.