We often get
questions related to tires and fuel efficiency. Do larger
tires improve gas mileage?
The common belief is that a tire with a larger diameter will cover more ground per revolution, thus reducing overall gearing and enabling the engine to run at lower revolutions per minute (RPM). People generally associate lower RMP with less fuel used to travel the same distance. While this may be true in a few instances, it is not the case for most vehicles. There are too many variables to make a universal statement that larger tires are more fuel efficient.
Changing the diameter of a vehicle’s tire can impact its overall performance including vehicle weight, acceleration, braking, and fuel economy. The biggest factor in how tire size affects economy is the engine’s torque curve, relative to vehicle weight. Smaller displacement engines produce less torque (twisting force) per revolution, and must spin at higher RPMs to make power. Engines are generally most efficient when running at the RPM at which they produce peak torque, or the greatest amount of force per revolution. A car should be geared so that it stays as close to the peak torque RPM as possible for greatest efficiency. If you have too large of a tire, the engine will fall below its range of optimal efficiency, requiring more fuel to stay running at the same RPM. If the tire is too small, the engine will be spinning faster than necessary to maintain speed, thus wasting power and fuel.
In a nutshell, the vehicles which stand to benefit from a larger diameter tire are those that produce more torque than they need to in order to maintain speed. This can include cars which have a final drive gear ratio optimized for acceleration (like sport package Civics and the Dodge Charger R/T), or Diesel trucks and cars that always produce torque in excess to drive speed (such as the Ford F-350 and Volkswagen TDi). Diesel-powered vehicles can almost always stand to benefit from a slightly larger tire, since their peak torque occurs practically at idle.
Increasing the width of a tire can impact fuel economy as well. Wider tires create a larger contact patch, the area of the tire actually touching the road. While this is good for performance, it can create a higher resistance to coasting, meaning that the engine will have to use more power and fuel to maintain speed. Taller tires will also raise the vehicle higher further from the ground and can, according to BF Goodrich, increase its wind resistance and decrease its fuel economy.
There are just too many factors to consider to make general statements that larger or smaller tires are more fuel efficient. If you have any questions about the right size tire for your vehicle, please contact the nearest Dunn Tire for professional assistance.