Bottom bracket, in particular of a bicycle with auxiliary electric drive, comprising - a drive shaft, which is provided to be connected to two pedals, - two rolling bearings (5, 6) of different dimensions, supporting the drive shaft, - a measuring sleeve which is arranged between the rolling bearings (5, 6), encloses the drive shaft, is provided to measure the sum of the torque introduced into the drive shaft from the two pedals and is rotationally fixedly connected to the drive shaft by means of toothing, - an output sleeve which is arranged in the axial extension of the measuring sleeve, is rotationally fixedly connected to the latter and is provided to be connected to a chain-wheel carrier, - a sliding bearing between the output sleeve and the drive shaft, - an encoder, which is arranged at the end of the measuring sleeve, on the side facing away from the output sleeve, and which is provided to measure the rotational speed and direction of rotation of the drive shaft, characterized in that the bottom bracket has an evaluation unit surrounding the measuring sleeve coaxially, which interacts with the measuring sleeve and with the encoder, wherein - the rolling bearing adjacent to the output sleeve has smaller rolling elements than the rolling bearing adjacent to the encoder, and wherein - a first side of the evaluation unit, facing the encoder is kept rotationally fixed relative to an outer ring of the rolling bearing adjacent to the encoder by a snap-in contour, and, on a second side of the evaluation unit, facing the chain-wheel carrier, the said evaluation unit has an auxiliary mounting contour projecting radially outwards, which is designed to safeguard against erroneous mounting of the evaluation unit. - a drive shaft, which is provided to be connected to two pedals, - two rolling bearings (5, 6) of different dimensions, supporting the drive shaft, - a measuring sleeve which is arranged between the rolling bearings (5, 6), encloses the drive shaft, is provided to measure the sum of the torque introduced into the drive shaft from the two pedals and is rotationally fixedly connected to the drive shaft by means of toothing, - an output sleeve which is arranged in the axial extension of the measuring sleeve, is rotationally fixedly connected to the latter and is provided to be connected to a chain-wheel carrier, - a sliding bearing between the output sleeve and the drive shaft, - an encoder, which is arranged at the end of the measuring sleeve, on the side facing away from the output sleeve, and which is provided to measure the rotational speed and direction of rotation of the drive shaft, characterized in that the bottom bracket has an evaluation unit surrounding the measuring sleeve coaxially, which interacts with the measuring sleeve and with the encoder, wherein - the rolling bearing adjacent to the output sleeve has smaller rolling elements than the rolling bearing adjacent to the encoder, and wherein - a first side of the evaluation unit, facing the encoder is kept rotationally fixed relative to an outer ring of the rolling bearing adjacent to the encoder by a snap-in contour, and, on a second side of the evaluation unit, facing the chain-wheel carrier, the said evaluation unit has an auxiliary mounting contour projecting radially outwards, which is designed to safeguard against erroneous mounting of the evaluation unit.