Rolling Resistance and Fuel Consumption

Rolling resistance refers to the various forms of resistance against driving force when the car is in motion. Several factors contribute to rolling resistance, including wind drag on the car, acceleration resistance generated by inertia force when speeding up, and resistance on the tires.

(A) Resistance on car  (B) Resistance on tires
(1) Inertia (2) Wind drag  (3) Acceleration resistance  (4)Rolling resistance
(5) Impact on tires (6) Wind drag  (7) Tire distortion  (8) Friction with the ground
 

Loss of energy due to tire distortion when driving

As a tire flexes when it rotates, friction between molecules causes energy to be converted to heat. This is known as hysteresis loss. Such loss accounts for the majority of all rolling resistance in a tire (approximately 90%). Rolling resistance is lower in radial tires than bias tires, and decreases with low-aspect tires that have high tread rigidity.

Hysteresis loss occurs when this section gets distorted

When force is applied to rubber (viscoelastic body), energy is converted to heat and then lost as the shape changes. For that reason, it is imperative to keep air pressure at an appropriate level to suppress unnecessary distortion and minimize energy loss.

Relation between rubber (viscoelastic body) distortion and force (1) Force (A) Force (B) Distortion (C) Energy loss

Loss of energy from friction when tread rubber touches the ground

Although differing by road surface condition, tire type and tread pattern, resistance caused by friction between the tire and the ground accounts for less than 10% of total rolling resistance.

Loss of energy from wind drag as tires rotate

Resistance is extremely minimal at low speeds and can be ignored.

Relation between resistance and speed
(A) Driving resistance index (B) Speed(km/h)
(1) Resistance caused by power transmission
(2) Rolling resistance  (3)Wind drag
Driving resistance increases sharply the faster you drive.
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