It may seem like an obvious thing to say that steer tire inflation is incredibly important, yet some motor carriers and truck drivers simply don’t understand what kind of a difference a mere 5 or 10 pounds of inflation pressure can have on the way a commercial motor vehicle operates. It may seem like an insignificant number, yet it could make the difference between getting somewhere safely or winding up in collision or tragic accident.
Take for example, the deadly crash that happened just before Labor Day weekend in New Mexico. A tractor-trailer suffered a blowout on one of its steer tires and crossed over the median, hitting a greyhound bus head on. When authorities examined the tire that blew out, it showed all the signs of being underinflated. When the tire blew, the truck driver lost control of the truck, leading to a tragic accident that potentially could have been prevented.
While the cause of the crash has not been officially determined, the shredded tire hanging off of the left front wheel is most certainly drawing the attention of National Transportation Safety Board investigators. No matter what the cause of that accident ends up being, it is incredibly important that fleets and truck drivers understand: 100 psi in a steer tire is not okay.
The Pressure is On
Yes, for drive and trailer tires, it is pretty common to see 100-psi as the widely-accepted inflation level. Some even wonder why they should inflate to such a pressure when load tables commonly call for 75 and 82 psi for a duel tire supporting a load of 4,250 pounds, specifically when said tire is operating in a tandem grouping of 34,000 pounds.
The fact is, it is important that tires have a little extra 20 pounds of pressure, or thereabouts, to provide a cushion in case there is a slow leak or other unseen problem with the tire. Extra tire inflation can also stiffen the sidewall, which reduced rolling resistance and increases overall fuel efficiency.
In fact, when it comes to steer tires, there is a completely different paradigm to consider. Inflating steer tires to 100 psi may have been acceptable a decade ago, but today, with increased load-carrying capacities and changes in structural designs to emissions-equipped, set-back axle vehicles tractor-trailers, 100 psi is simply not enough.
If you were to examine most load tables today, a typical tire will need 105 psi to safely handle a carrying capacity of 12,000 pounds per axle. Low profile tires require a different kind of consideration. For a tractor running 22.5-inch low profile steer tires, 110 psi is appropriate. The days of considering 12,000 pounds as the standard steer axle weight have come and gone.
Changes to the way trucks are built have pushed this new paradigm. With all the new add-ons, it is important to look at the extra load that steer tires now have to bear. Thinking traditionally about the amount of weight on a steer tire can be dangerous.
Response to Underinflation
In the early 2000s, people were using the same 95 to 100 psi target when evaluating steer tires and the standard steer axle was only 12,000 pounds. Take a look at a Class 8 commercial motor vehicle being minted at factories today and you will routinely run into examples of steer axles heading north of 13,000 pounds.
With so much weight now being shouldered by the steer tires, many tire manufacturers provide a uniform method for increasing the load capacity on a tire. First, you can increase the volume of air in a tire or increase the pressure of the air within a tire, both accounting for the tire’s given size.
It is also important to consider the load range, which is the tire’s rating for how much weight it is capable of carrying at a given pressure, while still maintaining the same footprint and sidewall flex. While tire makers may go different routes in determining these factors, the federal government provides specific industry standards that OEMs must comply with.
This leads many to ask what the ideal load range and inflation would be for a steer tire? Unfortunately, there is not one answer. Fleets must make sure they are conducting axle-weight tests on each load a vehicle carries over a specified period. They also need to make sure they are accounting for the fuel on board. Not accounting for all the fuel during checks could leave a several hundred pounds from appearing.
Upon discovering what your steer axle loads are, it is important to initiate a conversation with whomever you get your tires from. The new standard should always be 110 psi for 12,000 pounds and 110 psi to 115 psi for anything higher than that. Do not hesitate to lean on a tire supplier for specific, manufacturer-provided recommendations. They will generally have their own internal data books that provide information on load ratings and sizes for particular loads.
Keeping an Eye on Inflation Issues
The only way a tire goes from functioning properly and inflated to its correct level to a complete blowout is if it hits something on the highway, otherwise, the problem is likely the result of air loss or improper inflation levels. It is critically important the inspection checks focus on how inflated the steer tires are, as this can uncover other, unknown issues.
It is very likely that a large number of blowouts on the roads today could easily be prevented if the tires on the vehicle were kept to their proper inflation level. Yet, there are motor carriers out there that still don’t pay proper attention to tire inflation.
Most within he industry hold an expectation that a tire in perfect condition will still loose 2% of its inflation pressure, by volume over a 30-day period. While this is largely true, the problem with thinking such a way is that it leads truck drivers and shop technicians thinking they only need to check their steer tires once every 30 days, which is absolutely not true.
It is not outside the realm of possibility to find an imperfectly sealed tire or wheel assembly. When you think everything is just as it should be, there could be air seepage coming from the tire as high as 2% every 7 days. Add in puncture wounds or problems with a valve stem and you may be looking at 2% per day. If a truck driver or motor carrier is not checking a tire that loses 2% of inflation pressure, by volume, per day, they could be looking at a catastrophe just waiting to happen.
It is critical that motor carriers build their tire maintenance program not round what they consider normal air loss, but instead to evaluate all the factors associated with the steer tires, from irregular wear to decreased fuel economy. The last thing anyone wants is a blown-out tire that has resulted from excessive sidewall flex or compound deterioration.
Evaluating Road Speed
While this may not come up as the first thing one thinks about when evaluating steer tire pressure, road speed is an important factor in impact and tire inflation. There are few major manufacturer tires that are rated for less than 75 mph. If you discover a brand that rates for 65 mph or less, run for the hills, you are likely dealing with an off-shore brand where the reliability of the tire is in question.
Speed also comes into play where tire mismanagement is concerned. If your steer tires are underinflated, whether through neglect, mismanagement, or otherwise, you may be exceeding the speed capacity of the tire without even realizing it.
Consider that tire manufacturers set their ratings based on the assumption that the tire is properly inflated to begin with. This is why it is important that extra attention is paid to steer tires and that there isn’t a fear of over-inflation.
Finally, application is important. There is always the potential that tires could be run in applications that they were not originally intended for. Whether it be urban, regional, or otherwise, if a tire rated for streets is used on a long-haul highway truck, the consequences could be disastrous. Leaning on the tire manufacturer to ensure the recommended use is followed could be the only thing between a motor carrier operating safely and winding up with an accident on their hands.
In the end, remember that 5 to 10 psi on steer tires can make a world of difference. Ensuring you are using the correct size steer tire based on the proper load-range of the steer axle should not be optional. Ensuring proper tire maintenance and checks go a long way to ensuring that inflation is not the only thing you are worrying about. Safety is key, and steer tires are critical to safe truck driving.