Here’s how tire pressure actually affects gas mileage – Jalopnik

Every time you fill your fuel tank you can feel the competitive fuel prices and promise that you will be driving on a lighter foot. But your driving habits don’t have to be the reason you use less gas, as under-inflated tires are often the cause. Underinflated tires compress and sag under the weight of the vehicle, increasing rolling resistance. This forces the engine to work harder than it would at the manufacturer’s recommended tire pressure, and as the engine works harder, it burns more fuel, ultimately decreasing efficiency. Driving with low pressure may not harm your transmission or other major components, but it will certainly put more strain on your car.

A study of Oak Ridge National Laboratory showed that tires operated at 25% less than the recommended pressure experienced a 2 to 3% decrease in fuel consumption. A 50% reduction in tire pressure resulted in a 5–10% reduction. In winter, you should pay particular attention to your car’s tire pressure, as it drops further in colder temperatures, decreasing by one or two PSI for every 10 degree drop. This happens because as the air cools, it contracts and becomes denser, reducing the pressure in your tires.

Each vehicle has its own recommended tire pressure, which can be found on the driver’s side door jamb and in the owner’s manual. Never inflate your tires to the pressure listed on the tire, as that number refers to the maximum pressure for that tire and not the recommended pressure. In addition to reducing miles per gallon, an underinflated tire can also cause serious damage to the structure of the tire, causing it to lack sufficient grip on the road.

Vehicle manufacturers take several factors into account when setting the correct tire pressure, including safety, tire life, fuel consumption and driving behavior. Since modern cars are equipped with systems designed to monitor tire pressure, it is easier to keep track of it yourself. Make sure you don’t ignore the constant warnings from those systems and that you inflate the tires to the correct pressure.