Rullemotstand

Rullemotstand, often referred to as rullmotstånd in many Nordic languages, is the resistive force that opposes the motion of a rolling tire or wheel on a surface. It is a key component of a vehicle’s total energy losses and is primarily produced by the deformation of the tire as it makes contact with the road, along with hysteresis losses in the tread and carcass, and viscous losses in the tire materials and bearings. Air drag acts separately and is not included in rolling resistance.

The force of rolling resistance can be expressed approximately as F_rr = C_rr · N, where N is the normal load and C_rr is the rolling resistance coefficient. C_rr depends on tire type, inflation pressure, temperature, road surface, and speed. In general, higher inflation pressure and smoother surfaces reduce C_rr, while heavier loads or softer tires increase it. Values vary widely by application; road car tires on smooth pavement typically exhibit a small coefficient, while off-road tires or heavily loaded conditions yield higher resistance. For bicycles, C_rr values are often in the lower range, influenced strongly by tire construction and pressure.

Measurement and assessment of rullemotstand are conducted using standardized tests on rollers, dynamometers, or road trials to determine C_rr under controlled conditions. The concept is fundamental in vehicle energy efficiency studies, as rolling resistance directly affects required propulsion power and, consequently, fuel consumption and vehicle range, especially for electric vehicles. Designers seek low rolling resistance tires and optimized suspension and drivetrain layouts to minimize energy losses without compromising grip and safety.

See also: rolling resistance coefficient, tire design, energy efficiency.