Traction or friction measuring device and calibration method

The invention relates to a traction or friction measuring device and a calibration method. The apparatus includes a flat disc traction surface; a spherical ball traction surface constructed and arranged to be in contact with the disc traction surface in use; a support structure constructed and arranged to support the disc and ball traction surface relative to each other while allowing a relative rotational movement therebetween; about the axis, the disk drive means and the ball drive means are operable to effect relative movement between the disk and the ball traction surface, and include disk speed measurement means and ball speed measurement means to produce traction or friction therebetween; and a force measurement device associated with at least the disc and ball traction surfaces to provide a force measurement resulting from the traction or friction, and measurements of the ball speed and the disc speed can be made at pure rolling points between the ball and the disc in order to accurately determine the