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Researchers at Oak Ridge National Laboratory recently conducted a study that measured the effect of tire pressure on fuel economy at speeds ranging from 40 to 80 miles per hour. The figure below shows the results of a 2009 Toyota Corolla tested with all four tires at the recommended pressure (Black line), then at 75% of the recommended pressure (green line), and again at 50% of the recommended pressure (orange line). With all four tires at 75% of the recommended pressure, the fuel economy penalty remained fairly consistent at about 2-3% over the range of speeds. The fuel economy penalty for all four tires at 50% of the recommended pressure is more severe but the effect on fuel economy is greater at lower speeds. At 40 miles per hour, fuel economy with all four tires at 50% of their recommended pressure is about 10% lower but at 80 miles per hours it is only about 5% lower. It should be noted that underinflated tires not only waste fuel but also pose serious safety risks.
Fuel Economy by Speed for a Toyota Corolla under Various Tire Pressure Conditions
(miles per hour)
|Recommended Tire Pressure||75% Tire Pressure||50% Tire Pressure|
|Fuel Economy (miles per gallon)|
|Note: The vehicle tests consisted of a warm-up phase to a target oil temperature, followed by a 50 mph cruise for five minutes and then operating the vehicle at steady speeds from 40 mph to 80 mph in 5 mph increments, with each speed held for at least 5.5 minutes.For additional detail on the individual tests, see the source listed below.
Source: J., Huff, S., and West, B., "Fuel Economy and Emissions Effects of Low Tire Pressure, Open Windows, Roof Top and Hitch-Mounted Cargo, and Trailer," SAE International Journal of Passenger Cars -Mech. Syst. 7(2):2014, doi:10.4271/2014-01-1614.