What effect does low air pressure in tires have on fuel mileage?

Low air pressure in tires decreases fuel mileage due to increased rolling resistance. When tires are not inflated to the recommended pressure, they create more friction with the road surface as they flex and deform. This additional resistance means the engine has to work harder to maintain speed, leading to increased fuel consumption. Essentially, under-inflated tires require more energy to move, which directly results in lower fuel efficiency.

Maintaining proper tire pressure is essential not only for optimal fuel economy but also for safety and tire longevity. Adequate pressure helps ensure that the tires maintain their intended shape, providing better handling, traction, and stability while driving. On the other hand, no effect or an increase in fuel mileage would imply that tire pressure has no significant influence on vehicle performance, which is not accurate as the vehicle's efficiency relies heavily on many mechanical factors, including tire condition and air pressure.