Kugelumlauf

Kugelumlauf, commonly translated as “ball‑roll test,” is a laboratory method for determining the rolling resistance of tyres, rollers, or other circular components. The technique involves a metal or ceramic sphere that is set into perpetual motion on a flat, lubricated test surface; the torque required to maintain a constant angular speed is measured and related to the rolling resistance coefficient of the specimen.

The test apparatus consists of a rigid turntable, a drive motor with precise speed control, a torque transducer, and a sphere of known diameter and material. The specimen—typically a tyre or roller—is mounted on the turntable, and the sphere contacts its outer surface while the motor drives the assembly at a prescribed speed (often 30–200 rpm). The measured torque is corrected for friction in bearings and air resistance, then expressed as a dimensionless coefficient or as resistance force per unit load. Standardized procedures are defined in ISO 28580 and in various automotive and railway specifications, which prescribe test temperature, load, surface preparation, and calibration of the sphere.

Kugelumlauf is valued for its repeatability, relatively low equipment cost, and ability to test a wide range of sizes without extensive modification of the rig. It is widely used in tyre development, roller‑bearing qualification, and in the evaluation of conveyor‑belt rollers. Limitations include sensitivity to surface contamination and the fact that the test does not replicate all dynamic effects present in real‑world operation, such as transient loads or varying slip angles. Nonetheless, it remains a cornerstone laboratory method for assessing rolling resistance in many engineering fields.