Abstract: The invention relates to a method and apparatus for installing belts on belt drives of the type where the belt is tensioned on the belt drive with the use of an adjustable tensioning device. In order to avoid a rapid slacking of the adjusted belt tension, the belt is driven in a preconditioning device at a defined tension value for a predetermined period or time. The belt is preferably installed on the belt drive immediately after removal from the preconditioning device. The preconditioning device includes a drive motor for driving a first pulley, a second pivoted pulley, and a tensioning device for tensioning the belt while it is carried by the pulleys.