It took one flat tire to convince Marshall Sumner that his car needed tire-pressure monitors as an early-warning system.
Sumner, a computer programmer, was cruising on a crowded southern California expressway last year when his Cadillac Catera began making loud thumping noises. First, he thought the transmission had broken but then realized a rear tire had gone flat and the tread was coming apart.
Stuck in a middle lane, Sumner had to gingerly drive about a mile and a half before he could safely pull onto the shoulder.
“I don’t think I ran over anything, so the tire probably was just out of air. I decided then I really wanted tire-pressure monitors on my next car,” said Sumner, who admits he doesn’t check his tires regularly with a gauge.
His next car, a 2003 Cadillac CTS, didn’t come with tire-pressure monitors (TPMs), so Sumner had an aftermarket system installed for about $300.
“It took a lot of hunting on the Internet to find it, but I’m a gadgeteer, and this is the gadget I wanted on my car,” he said.
Congress mandated TPMs in 2000 in response to the Firestone tire recall and nearly 300 deaths from rollover accidents in Ford Explorers, most with Firestone tires.
TPMs are supposed to warn drivers of low air pressure, cited as a key factor in Firestone tire failures. Low pressure makes tires run hotter and weakens the rubber, leading to blowouts or tread separation.
Automakers were to phase in TPMs on new vehicles beginning with the 2004 model year, but the mandate is on hold because a federal court recently threw out regulations set by the National Highway Traffic Safety Administration and ordered NHTSA to draft new ones, a process that will take several months.
In the meantime, automakers are voluntarily installing TPMs on cars and light trucks, and suppliers such as SmarTire , which makes the system installed on Sumner’s Cadillac, are selling them through tire and parts stores.
General Motors was the first to offer TPMs, on the 1994 Chevrolet Corvette with run-flat tires, and the auto industry estimates they have been installed on more than 4 million vehicles. Most manufacturers offer them as standard or optional equipment on at least some 2004 models.
There are two types of TPMs. Direct TPMs have pressure monitors on each wheel and warn when any tire is at least 25 percent low through a warning display on the dashboard. The direct type also provides continuous pressure readings for each tire.
Indirect TPMs use anti-lock brake sensors to measure differences in rotational speed among the four wheels and warn when one tire is least 30 percent below the others. Indirect systems do not specify which tire is low.
At the request of the auto industry and under pressure from the White House, NHTSA adopted regulations last year that allowed indirect TPMs. Consumer advocacy groups challenged the rules, contending are ineffective because all four tires can be underinflated and not set off a warning.
A federal judge agreed and threw out the rules. NHTSA is writing new rules that specify direct TPMs.
With millions of TPMs on the road, consumers who have them generally praise them.
Rich Wegel, a retired engineer from West Chicago, credits a direct TPM system with alerting him to a leaky tire on a used 1998 Corvette he bought.
A Goodyear store inspected the tire and found nothing wrong, yet Wegel continued to get low-pressure warnings. He returned to the Goodyear dealer and insisted it remove the tire from the wheel for a closer look, and that’s when it found a puncture that hadn’t been fully sealed.
After the tire was fixed, the low-pressure warnings ceased. Wegel has replaced his Corvette with a CTS that doesn’t have TPMs.
“I wish it did. I think they’re excellent,” Wegel said, adding that his experience with the Corvette made him give his tires closer scrutiny. “Since I had the tire-pressure monitors, I probably check tire pressure a little more often.”
Winston Ashazawa had two tires on his Lexus SC430 punctured by nails. Both times, the car’s TPM alerted him before the tire went flat.
However, Ashazawa encountered problems with a direct TPM system on his 2004 Volkswagen Touareg. Within a week of delivery, it warned that the right rear tire was low, though it was fully inflated. Two weeks later, it gave the same warning for the left rear tire.
Volkswagen recalled the TPM system, but it still took a dealer a week to fix the problem, which required adjusting an antenna that sends pressure readings from the tires to a central receiver. Ashazawa was miffed it took so long to fix, but he says the system now works.
“I found it to be a lifesaver in the Lexus, and I expect it to be the same in the Touareg. I’m like most people, I should check the tires once a month, but I don’t,” he said. “It will have its teething problems like any new technology, but it’s going to make tire safety less of an issue.”
Discussion boards on Edmunds.com, an automotive consumer site, show Ashazawa isn’t the only one experiencing problems with TPMs. Another Touareg owner said his TPM warning lit up when a tire dropped one pound below the recommended level, and he couldn’t turn it off.
A Murano owner said his Nissan dealer said it couldn’t rotate the tires because the TPMs work at only one location. (Direct TPMs can be rotated but need to be recalibrated with a magnetic tool.)
Barry Lustig learned that after having the tires rotated on his Cadillac DeVille DHS. He started getting erroneous warnings about low-pressure because his Cadillac dealer forgot to recalibrate the monitors.
“Even the dealers will forget to reset them, so now when I take the car in I tell them it has tire-pressure monitors,” said Lustig, an optician who says the TPM system alerted him that a screw had punctured a tires.
One befuddled owner on Edmunds said the direct TPM on his Infiniti FX45 was “really nice but the display is confusing because it does not label which reading belongs to which tire, which I find rather odd.”
Infiniti spokesman Bill Garlin says tire pressures are displayed “in a random order,” and if one is low, the driver is advised to check all four.
“But at least you know to check,” Garlin said, adding that FX45’s owner’s manual explains how the system operates.
The same Infiniti owner also wondered, “During stop-and-go driving the readings fluctuate from 32 p.s.i. to 37 p.s.i. Is this normal?”
Yes, according to the tire industry, which found in a survey this year that only 43 percent of drivers check their tires at least monthly.
John Rastetter, chief tire tester for the TireRack, a mail order and Internet retailer based in South Bend, Ind., says pushing a button on the dashboard to check tire pressures can be misleading.
Tires that have been sitting in the hot sun for a few hours may read 5 p.s.i. higher than normal, for example, and tires lose about one pound of pressure for each 10-degree drop in air temperature.
Rastetter says consumers still need to check inflation with a gauge when the tires are cold and inspect the tires for nails, cuts and other damage.
“If you don’t check your tire pressure and look at your tires, you’re still not going to get the performance and durability you should,” Rastetter said, adding that underinflation does more damage than slight overinflation.
“Running at 30 percent below normal tire pressure is like running your engine two quarts of oil low,” he said. “It makes the tire work harder, it gets hotter and it won’t be as responsive.”
Tire Rack recently let journalists drive BMW 3-Series sedans on a handling course at its South Bend headquarters with tire pressure on one car set at the recommended levels of 29 p.s.i. front and 32 rear and the other underinflated by 25 percent. The car with underinflated tires slid more in tight turns, didn’t stop as quickly and didn’t steer as precisely.
“You are much better off being slightly over inflated than being too low,” Rastetter said.
