Trouble with Tire Pressure Monitoring Systems

The most idiotic of all “idiot lights” in your car may be the Tire-Pressure Monitoring System (TPMS). The problem isn’t with the TPMS itself. Rather, it’s that the TPMS light doesn’t illuminate until your tires are severely or, possibly, dangerously underinflated. Imagine a burglar alarm that doesn’t go off until the bad guys have already carried out the TiVo.

Lights On, Anybody Home?
If the TPMS light is not illuminated, many drivers assume their tires are fully or, at least, adequately inflated. Often, they are wrong. Many who used to regularly check tire pressure will stop doing so, incorrectly assuming TPMS now takes care of that chore. And many will continue driving long after the TPMS light glows: Idiots often ignore idiot lights. Even the shape of the TPMS warning symbol—an exclamation point inside a slice of a tire—isn’t too bright because many don’t recognize its meaning.


The reason the federally mandated pressure-monitoring devices are arguably worse than worthless is that government regulations do not require the systems to provide a warning until a tire is 25 percent underinflated. When underinflated, even brand-new tires can’t overcome deep water. Also, underinflated tires don’t provide enough grip for emergency accident-avoiding maneuvers on damp or even dry pavement.

Underinflation Dangers
But here’s something that’s even more important: When underinflated 24 percent—the TPMS warning light is not glowing—a tire’s internal components may be overheating and deteriorating. The Rubber Manufacturer’s Association says that tires on some vehicles are barely able to carry a full load even if tire pressure is set exactly to the vehicle manufacturer’s recommendation. The AAA says that tires are “well below the pressure required for safe driving” when underinflated by 25 percent. (For new cars, the correct tire pressure is on a placard on the driver’s doorjamb. In older cars, it can be many places including the lids of the glove box, trunk or center console.)


Tire-pressure monitoring systems were mandated by the TREAD Act passed by the U.S. Congress in 2000. TMPS have been on all new cars since the fall of 2007 and were on some cars well before that. A National Highway Traffic Safety Administration (NHTSA) spokesman said TPMS regulations were meant to warn only of “imminent tire failure.” Several tire makers and a consumer-watchdog group sued the Federal government to raise the TPMS threshold, but lost.

It’s air pressure that allows a tire to carry a load.
It’s air pressure that allows a tire to carry a load. To picture this, lay a new, full, unopened two-liter plastic soft drink bottle on its side, hold onto something solid and step up onto the bottle. Then, empty the bottle and stand on it again.


An underinflated tire won’t immediately burst if you fill your minivan with high school football players or your pickup with gravel. Instead, the tires will flex too much and overheat, which will begin to break down the internal components, as well as chemical bonds between components. The damage is permanent and adds up over time. Under-inflate or overload a tire often enough and it will come apart, sometimes long after the harmful incidents. It’s kind of like when your fat uncle sat on the antique chair at Thanksgiving: The damage it suffered will cause it to collapse when your frail grandmother uses it at Christmas. Damaged tires are most likely to fail at high speed on a hot day with a heavy load aboard: Summer vacation is prime time for tire failure.