Trick question: Would you say that most of the tires on commercial vehicles today are overinflated or underinflated?
The surprising answer, according to Rick Phillips, director of commercial sales, Yokohama Tire Corp., is that most of the tires (drive and trailer) on commercial vehicles are actually overinflated.
The reason for this is that many fleets set their inflation standard at 100 PSI per tire for all wheel positions, Phillips noted. However, on a Class 8 truck and trailer combination equipped with size 295/75R22.5 tires, for example, the total carrying capacity at 100 PSI would be more than 94,000 lbs. Most vehicles are simply not grossing out that heavy, and if they are not, the tires on that vehicle are overinflated. A common misconception today with the rising price of diesel is that by overinflating the tires, rolling resistance will be lowered and a large amount of money spent on fuel can be saved. That is simply not the case. The difference in rolling resistance between a properly inflated tired and one that is overinflated by 10% would be very minimal It would be even less noticeable—in fact insignificant—at the pump. While too much air is usually better than not enough air, it still will cause problems with the tire’s performance and in extreme circumstances may even cause the tire to fail prematurely. This reduced tire performance would actually negate any savings in fuel consumption.
Regarding the steer tires on that same truck, at 100 PSI there may actually be a chance that the steer tires are underinflated. When you consider some of the new engine components to comply with emission regulations, heavier loads, and sliding the 5th wheel forward to reduce the trailer gap and wind resistance, chances are good that the front axle will actually require more than 100 PSI to carry the load. Overloaded/underinflated tires can lead to serious problems, especially when they are on the steer axle, Phillips said.
He went on to say that in the design process, tire engineers use the latest technology to decide exactly where and how much the tire will flex during operation. The same is true for determining the precise size and shape of the tire’s footprint as it rolls across the road surface. If the tire’s inflation pressure does not match the load it is carrying, all of this technology is wasted and the tires will never perform up to expectation, which will result in a higher cost of operation for the fleet.