You've heard it before, but the importance of maintaining tire pressure needs to be understood by everyone associated with your vehicles. 

Ask any tire manufacturer to name the single most important factor for increasing tire life, the answer will be maintaining proper air pressure. Since there probably isn't a fleet maintenance manager alive who hasn't heard that statement, why keep talking about it? 

Easy! The gospel of proper air pressure needs to be preached --- and practiced --- beyond the core of true believers. Keeping an eye on tires needs to be the responsibility of everyone in the fleet from the maintenance technicians to the drivers. The cost of driving underinflated tires is significant enough that maybe everyone in the fleet should be issued a tire gauge on the day of employment. 

Okay, that may be a bit extreme, but the idea of placing more emphasis on the day-to-day care of tires will save fleets money----and isn't that what good maintenance is supposed to do? 

Recently, using its own information and resources such as The Maintenance Council (TMC) and Rubber Manufactures' Association (RMA), Bridgestone/Firestone released data on the cost impact of low tire pressure. What they documented supports what the industry has been saying for years. 

Correct inflation pressure can minimize many types of irregular wear, which means higher tire removal mileage and reduced tire handling costs. Tires rotate about 500 times for every mile traveled, so in 100,000 miles every part of the tread gets pressed against the pavement some 50 million times. Since uneven, irregular wear is the result of uneven abrasion, tires need to press against the pavement the same way every time. Having the tire maintain a consistent shape throughout its life helps a lot. 

TMC reports that 10 percent underinflation will shorten tread life by 9% to 16%. If we use an average tire price of $250., such underinflation costs about $25. per tire. In addition, because the tires will be changed more often, there will likely be increased service costs as well as more vehicle downtime. 

How may drivers and maintenance people, if they had a target inflation pressure of 100 psi, would consider 90 psi (10% underinflated) "Close enough?" TMC suggests that each 10% results in a similar loss of tread life. Running a tire that's 20% underinflated could cost $50 per tire. If underinflation exceeds even 10%, there may be bigger problems --- excessive flats and emergency road service calls that could cost anywhere from $100 to $1,000. 

Both TMC and RMA recommend that tires found to be underinflated by 20% or more be removed from service immediately, demounted, and inspected for damage. 

As for fuel economy, underinflation causes more sidewall flexing, or what tire engineers call deflection, which consumes more energy and uses more fuel. In fact, underinflation by 10 psi will probably translate into about 0.5% decrease in fuel economy. A vehicle that currently gets 6 mpg would only achieve 5.97 mpg. While that may not seem significant, at 100,000 miles per year the extra 84 gallons of diesel fuel would be about $84.00 added cost per truck annually. 

Excessive deflection has other consequences. It weakens steel cords, which can lead to premature tire removal. Flexing also generates heat, which is an enemy of tire casings since heat ages tires. A fleet that wishes to get at least two retreads per casing will see that average drop to 1.5. If the casings are worth $60.00 to $80.00 the fleet would loose that investment. 

Inconsistent air pressure also affects duals. If the tires don't match in diameter, the smaller tire is dragged along by the larger one. This can result in extremely rapid and irregular wear on the smaller tire. If duals differ in inflation, their diameters can differ enough to cause this kind of problem. 

So what do you do to prevent air pressure problems? It's basic --- check pressure regularly using a good gauge that is calibrated often. To keep air in, keep wheels clean and properly lubricated. Make sure valve stems and cores are in good condition. 

The best tread designs and the most expensive tires are nothing without the air that carries them along. Checking tire air pressures is such a small investment in time compared to the costs related to replacing tires put out of service because of improper inflation. 

Originally appeared in a slightly different form in FLEET EQUIPMENT MAGAZINE. Reprinted with permission.