text: Tire Pressure Monitors Keep Drivers Informed - tribunedigital-orlandosentinel
  August 22, 2002|By Rick Popely, National Correspondent
  If you are like nearly one-third of American motorists, the last time you checked the air pressure in your tires was too long ago, and at least one tire is dangerously under-inflated.
  Under-inflated tires run hotter, wear faster and have greater chance of suffering tread separation and blowouts. The National Highway Traffic Safety Administration cited under-inflation as a cause of tread separation on Firestone tires, which has resulted in 271 deaths, many in Ford Explorers.
  That is one reason Congress two years ago, reacting to the Firestone recall and Explorer rollovers, mandated auto safety measures including tire pressure monitors on new vehicles.
  Under rules the safety administration issued in May, new vehicles must have tire pressure monitors under a phase-in schedule beginning Nov. 1, 2003. The agency will let automakers use two types of monitors the first three years -- direct and indirect.
  Direct systems have individual pressure monitors on each wheel that transmit a radio signal to activate a warning light when any tire differs significantly from a recommended inflation level.
  Direct monitors provide pressure readings whether a vehicle is moving or parked. The safety administration's rule requires direct systems to give warnings when any tire drops 25 percent below normal. For a tire that requires 32 psi, that would be 24 psi.
  Indirect systems operate off a vehicle's anti-lock brake system and measure differences in rotational speeds among the tires.
  They work only when a vehicle is moving. The agency's rule requires indirect monitors to warn when one tire is 30 percent or more below the others. So for that same 32-psi tire, that would be 22 psi.
  The Chicago Tribune tested two versions of each system that are available, and the direct monitors proved more effective and informative than the indirect type.
  The Alliance of Automobile Manufacturers estimates that more than 2 million vehicles on the road have tire monitors, the bulk of them GM models with the indirect type.