3. Tires

Tests that author Don Sherman helped devise and conduct at Car and Driver magazine found that dropping tire pressure from the manufacturers’ recommended 30 psi to 20 psi cost half a mile per gallon on a 37.5 mpg baseline (achieved by the car cruising at 60 mph with no modifications). When over-inflation by the same amount was evaluated, there was no discernible benefit.

Tests that Consumer Reports conducted on a Mercury Mountaineer and a Toyota Camry show that dropping only 2 psi from the recommended inflation pressure increases fuel consumption by 1 percent. Reducing inflation by 10 psi from the manufacturer's recommendation dropped the Camry's mileage by 1 mpg and the Mountaineer's "by a much smaller margin."

Tires are expensive to replace; proper inflation is the key to maximum tread life and reducing the likelihood of a blowout. Because tires tend to lose a couple of psi per month in cold weather, keeping a pressure gauge in the glovebox and checking pressure periodically is essential. Follow the carmaker’s inflation recommendations printed on a door jam placard, rather than figures printed on the tire sidewall. Also, the size and style of tire influences your mileage. Low-profile and wide tires tend to take a bite out of efficiency, as do winter tires. Sidewalls marked with energy symbols indicate that the tire was engineered with lower-than-normal rolling resistance.

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