AKRON—Just how bad is America's inflation problem? Tire inflation, that is.
The quick answer: pretty bad, according to an exclusive Tire Business survey.
In the wake of Bridgestone/Firestone Inc.'s recall of 6.5 million Firestone-brand P-metric light truck tires due to alleged tread separation problems, the issue of tire inflation has gotten more media attention and coverage than perhaps ever before.
When a tire is underinflated, its load-carrying capacity is reduced. Underinflated and/or overloaded tires flex more in use, which leads to higher running temperatures, and heat build-up is a primary cause of tread separation and resultant tire failure.
Given all the recent publicity surrounding tire inflation, we at Tire Business thought it appropriate to try to determine just how bad the inflation situation is out there. How many motorists are driving around on underinflated tires, and how underinflated are they?
Data gathered nationwide by the Car Care Council over the past four years, 1996-1999, indicated, on average, that about one in four passenger vehicles was running on underinflated tires. Our data suggests the situation is worse—much worse.
In a nationwide survey conducted the week of Oct. 15-21, Tire Business found that nearly three out of four vehicles (72.3 percent) were operating with at least one tire underinflated. For our purposes, "underinflated" means an air pressure below that recommended by the vehicle's manufacturer.
The Tire Business Inflation Pressure Survey was conducted as follows. Our Oct. 9 issue included an explanation of the survey and a survey form. All dealers were encouraged to participate and asked to randomly select customer vehicles, record the vehicle type, the manufacturer-recommend air pressure for both front and rear tires, and the actual air pressure in the front and rear tires.
Forty-two dealerships from all regions of the U.S. submitted survey results to Tire Business, with a total vehicle population of 766. By vehicle type, there were 436 passenger cars and/or minivans (subsequently referred to as the car category), 193 pickups and full-size vans (light truck or LT category) and 137 sport-utility vehicles (SUV category).
A sample form, as well as a full list of the participants, is available on the Tire Business Web site: www.tirebusiness.com.
Of the 766 vehicles in the survey, 554 (72.3 percent) had at least one tire inflated below the vehicle manufacturer's recommendation, with the average underinflated tire down by about 6 psi. Just over half the vehicles (51.0 percent) had at least one tire underinflated by 5 psi or more.
Forty-one percent of all vehicles had all four tires underinflated. (For more detailed results, see the chart on page 1.)
Among underinflated tires, rear tires tended to be slightly more underinflated than front tires, by 1-2 psi.
As a group, light trucks were more likely to be underinflated and by a greater amount than other vehicle types. Nearly half of all LTs (47.7 percent) had all tires underinflated, and by an average of almost 11 psi per tire.
The poor showing among light trucks maybe related to the fact that they tend to have higher recommended inflation pressures, and therefore more room to be underinflated. But it is at least a little troubling that the highest incidence of underinflation occurred in the category of vehicles most likely to carry a substantial load.
SUVs, as a group, had the lowest incidence of underinflation—perhaps not surprising since they are the vehicle type most closely associated with the Firestone recall. Still, three in five (59.9 percent) had at least one underinflated tire, though "only" about one-third (34.3 percent) had all four tires underinflated.
Was this a scientific survey? No. It is possible that the vehicles in our survey do not represent an accurate sample of the total U.S. vehicle population. Nor can we guarantee that all gauges used at all locations were accurately calibrated.
We also could not control for certain factors that influence tire pressure. Vehicle manufacturers' recommended pressures are "cold" inflation pressures, meaning that, for greatest accuracy, tire pressure should be measured early in the day, before rising ambient temperatures or the sun's radiant heat affect it—and before the vehicle has been driven more than a very few miles.
However, these factors tend to increase inflation pressure, so to the extent that the pressure readings in our survey were not cold readings, the actual rate of underinflation would be worse than reported.
Despite these potential flaws, one conclusion seems inescapable: A substantial majority of non-commercial vehicles on U.S. highways are operating with at least one tire underinflated, often by a significant amount, and a sizable minority are running with all four tires underinflated.
To the extent that underinflated tires affect vehicle performance, customer satisfaction and customer safety, there are facts those involved in manufacturing and servicing tires and vehicles might want to address.