Does Tire Size Improve Gas Mileage?

Written by tim plaehn Google
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The quest for better gas mileage should have us look at any factor that can improve the fuel economy of our cars. Tires are where a car contacts the ground and do have a significant effect on gas mileage. There are several considerations to weigh when wondering if changing tire size will improve the car's fuel economy.

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Considerations

Your car needs to overcome two forces to travel down the road: wind resistance and rolling resistance. Wind resistance is a results of the aerodynamics of the car and the speed at which it's travelling. Higher speed equals higher wind resistance, and that equals lower fuel economy. Rolling resistance is a factor of the road surface and how the tires interact with the road. Changing the features of the tires do affect rolling resistance and gas mileage.

Features

Modern cars are designed to work as a complete package. A car's fuel economy is a factor of engine efficiency, transmission and differential gear ratios, aerodynamics, wheel size and weight and tire size and construction. Car manufacturers use all of these factor to maximise the efficiency. Changing one of the factors---tires, for instance---without taking the others into consideration will usually reduce the fuel efficiency of the car.

Misconceptions

Changing the tires on a car so they're taller or shorter will provide a false change in perceived fuel economy. The speedometer of a car is calibrated to the revolutions per mile of the original tires, and changing tire size will result in an inaccurate odometer reading. Shorter tires will take more revolutions per mile, resulting in a higher calculated gas mileage using the uncorrected odometer reading. In fact, shorter tires will reduce fuel efficiency because the engine must run at a higher rpm to achieve the same speed and travel the same distance.

Theories/Speculation

If shorter tires reduce fuel mileage, do taller tires increase fuel economy? If you could get a taller tire without changing any other factors, the theoretical answer is yes. A taller tire will increase the weight and rolling resistance. However, the taller tire is also not designed for the gearing of the engine and drive train. If the car is a newer model, the computer will not know there is a taller tire and may cause the vehicle to run poorly and use more gas. Changing to taller tires will result in fewer tire revolutions per mile, but the offsetting factors will probably negate any theoretical fuel economy gains.

Potential

The one tire-size factor that can have a positive effect on fuel economy is tire width. A narrower tire will have less weight, less rolling resistance and less wind resistance. All are positive factors to increase gas mileage. But narrow tires could cause poor handling characteristics. The best way to increase fuel economy with tires is to buy tires constructed for better gas mileage in the size the car was designed to use. Keep the tires inflated to the recommended or slightly above recommended pressures but not above the maximum listed on the tire. This will reduce your rolling resistance and increase the gas mileage.

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