Tire Pressure Safety and Fuel Economy Tips

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A flat tire can create an immediate emergency situation, But there's another failure that must be addressed right away, a more insidious and subtle tire epidemic that's compromising both our tires and other areas of driving: underinflation. It's true, a large percentage of the vehicles on the road are operated with underinflated tires, and this can cause all kinds of problems. For one thing, it takes more energy to roll a tire with less air pressure, so the engine needs to consume more fuel. According to the American Automobile Association, underinflated tires can cut fuel economy by as much as 2 percent per pound of pressure below the recommended level. Underinflated tires also cause more heat to build up in the sidewalls. Heat is one of the primary enemies of tires, and excessive heat can cause the tire to fail prematurely or substantially shorten its service life, meaning you could be shelling out for new tires sooner than otherwise. Additionally, tires with low air pressure are more sluggish in their response to steering input and suspension dynamics, compromising your vehicle's handling, which could become a safety issue.
One of the easiest and most effortless solutions we've come across to keep tabs on underinflation is a wireless pressure monitoring system, such as the one made by SmarTire.
While we were doing our test with Uniroyal's NailGard tires, we also mounted a SmarTire system. Since the SmarTire system needs to be installed by a certified shop, we chose one of the most experienced custom installers in the Los Angeles area, Prestige Products (800/248-6483 or 213/749-8102).
  The SmarTire system consists of four sensors-one for each wheel-mounted to the rim inside of the tire. Each sensor monitors the air pressure and temperature and transmits this data via radio signals to a display module inside the cabin. When the vehicle is moving, air-pressure data is transmitted once every 30 seconds with an accuracy of plus or minus 1 psi (at 77 degrees F), while temperature information is transmitted once per minute. The sensors are powered by a lithium battery with a projected life of seven years or 90,000 miles.
To check it out, we first adjusted the cold pressure settings, inflating them from the recommended 26 psi to 32, in order to minimize abuse on the tires as we lost pressure. Then we set the system's initial alert at -5 psi under the cold setting and the second-stage warning at -10 psi. Next, we intentionally created a slow leak in two tires-a front and rear-by loosening the valve cores until we could hear a faint hiss. Finally, we took to the highway. The SmarTire system makes it easy to toggle between tires, getting a read on each with simply the press of a button. We watched as the normal tires slowly gained pressure due to the heat of driving, while the test tires either failed to gain pressure or gradually lost some. After 25 minutes of driving, the rear was only 2 pounds below its cold-pressure setting, while the front still held steady at 32.
To hasten the test, we stopped and loosened both valve cores a little more. After 15 minutes, the pressure alert light for the rear went off, signaling it had dropped 5 psi below the cold pressure mark. Unfortunately, with our module mounted atop the dash, the alert light was hard to notice without specifically checking for it; it's more visible at night, on a cloudy day, or if mounted in a dimmer location. Continuing to drive, we watched as the underinflated tires slowly built up more heat than the normal ones. Then, 35 minutes later, the pressure alert for the front went off and after about a minute, the pressure warning for the rear added its loudly beeping audio signal to the already illuminated alert light. Still, to the eye, neither tire looked dramatically different from the normally inflated ones. Finally, we loosened the front tire's valve core until it emitted a noticeable hiss, and within 10 minutes, the warning went off for the front tire, as well. (Along the way, we'd also gotten status warnings, alerting us to the fact that the actual pressure had deviated too far from the calculated "required pressure," which takes temperature into consideration.
  The system had worked perfectly. Without it, if one of our tires had actually developed a slow leak while on the drive, it's likely that we wouldn't have known about it until the tire was too flat to drive on. Moreover, it demonstrated its value in alerting us to the type of ultra-slow pressure loss that causes a general underinflation condition and all its unseen problems. In addition to a pressure drop, the SmarTire's temperature readouts can alert you to an unusual buildup of heat at a particular wheel due perhaps to an excessive load, bad wheel bearing, or brake overheating, a common problem on mountain roads.
The SmarTire system can be installed on virtually any car, minivan, or light-duty truck. It retails for $299, including installation, carries a 3-year/50,000-mile warranty, and is easily transferable between vehicles. The SmarTire system is included as part of the optional "Securitire" system in '96-'99 Lincoln Continentals and is approved for use with Michelin, Goodyear, and Bridgestone/Firestone run-flat tires. SmarTire USA, 888/982-3001. 
From Motortrend.com