Edmunds Earth Day Project: We Found 'Em Down, Pumped 'Em Up

Edmunds Earth Day Project: We Found 'Em Down, Pumped 'Em Up

More than Half of Vehicles Checked Were Wasting Fuel With Underinflated Tires

Volunteer checks tire pressure on 2000 Ford Explorer, one of nearly 500 vehicles checked during Earth Day project.

Running your vehicle on underinflated tires wastes fuel. That's a fact.  What's harder to come by are numbers showing just how many of us don't pump up to specifications and how much gas we end up wasting.

We're trying to get a handle on it here at Edmunds.com, though.

Last year, for Earth Day, our in-house Green Team checked the tires on 212 employee vehicles and found that, on average (figuring the average correct tire pressure to be 32 pounds per square inch, or psi), they were underinflated by 7 percent, or 2.24 psi.  And you'd think that at Edmunds we'd all be really car-savvy and never run around on tires that weren't in tip-top trim!

This year, we pushed out into the local community, setting up shop on Earth Day last Wednesday at a gas station near our global headquarters here in the People's Republic of Santa Monica and offering a free tire pressure check and, if needed, proper inflation, to everyone who came in for gas while we were there.

Our three shifts of volunteers, working from 9 a.m. until 3 p.m., checked the tires on 83 vehicles and recorded all the pertinent data.

We actually partnered for our Earth Day tire inflation project with a number of area businesses - car dealers, service stations and tire shops, mainly - and the 28 participating locales checked about 500 vehicles (we're still waiting for a few to report their numbers, so we don't have the exact tally yet). 

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Toyota of Santa Monica was one of Edmunds' tire pressure partners. Its technicians checked 144 vehicles on Earth Day.

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But we only recorded inflation data at the gas station manned by Edmunds volunteers, so that's what we'll deal with here.

Too Many Too Soft

After massaging the data, our crack analysts found that only 1 in 5 motorists was riding on properly inflated tires, while 29 percent of the vehicles we checked had overinflated tires and 52 percent were underinflated.

Even relatively new cars and SUVs with federally required tire pressure monitors were checking out underinflated - not because the owners were ignoring the pressure warning, but because the most commonly used monitors don't sound an alarm until at least one tire is down by 20 percent or more.

We found pressures that ranged from an impressive 22 psi overinflated (a Honda CR-V crossover with a ride like a rock) to a worrisome 17.8 psi underinflated (a Ford F150 pickup that was giving up 6 mpg because of its supersoft tires).

On average, those with insufficient air were running 5.6 psi below manufacturers' specifications. That's underinflated by 16.5 percent;  better than the estimated national average of 26 percent underinflation, but still not very good.

Those running overinflated tires were pumped up, on average, by an average of 5 psi too much. But overinflation, while contributing to excessive tire wear and reduced traction, doesn't have much impact on fuel economy.

Tire specialists who worry about such things tell us, though, that every 2.9 psi of underinflation  (that  would be the average of  all four tires) lowers fuel economy by one mile per gallon.

Our group of 43 softies was averaging a 1.9 mpg fuel economy reduction, collectively wasting 1,771.2 gallons of gas a year until we filled 'em up to proper specs last week and sent them off with warm wishes and a reminder that running underinflated tires not only wastes gas, it contributes to tire overheating and premature wear - even to blowouts - and ends up costing you money.

How Much?

At the present national average of $2.05 a gallon for regular unleaded gas and an average annual loss of 41.19 gallons to the ravages of underinflation, we figure our average driver with too-soft tires was spending an unnecessary $84.44 a year for fuel and spewing an extra 800 pounds of CO2 into the atmosphere in the process.

At $3 a gallon, that total annual cost of those underinflated tires would climb to $123.57 for each vehicle; it would hit $164.74 a year at $4 a gallon - enough to pay for a new set of tires every few years.

Of course, by keeping your tires properly inflated, you probably won't need a new set of tires that often, but that's another issue.

John O'Dell, Senior Editor

John O'Dell:  is an AutoObserver Senior Editor. Follow @AutoObserver on Twitter.