A continuously variable gear is described having an input shaft, a plurality of traction balls distributed radially around the axis, each traction ball is mounted on an axle passing there through, the axles are tiltable in the radial grooves in the housing and support plate. To control the position of the traction balls, the axles are guided in curved slots of a turnable iris plate. To control the axial placement of the traction balls, there is a rotatable input disc positioned adjacent to the traction balls, a rotatable output disc positioned adjacent to the traction balls opposite the input disc, and a pre-spanning ring around the traction balls such that each of the traction balls is making three-point contact with the input disc, the output disc and the pre-spanning ring, the contact surface of the pre-spanning ring having a specific curvature larger than the radius of the traction balls.