Method of controlling target speed of rotating member used in image forming apparatus

An image forming apparatus comprising:

• a first image forming unit having a first photosensitive drum that rotates, the first image forming unit configured to form a first image on the first photosensitive drum by using black toner;
• a second image forming unit having a second photosensitive drum that rotates, the second image forming unit configured to form a second image on the second photosensitive drum by using chromatic color toner;
• an intermediate transfer member on which the first image and the second image are transferred;
• a transfer member configured to transfer the first image and the second image from the intermediate transfer member to a sheet;
• a motor configured to rotate the intermediate transfer member;
• a controller configured to:
• control the intermediate transfer member in a first mode in which the intermediate transfer member contacts the first photosensitive drum and the second photosensitive drum, and
• control the intermediate transfer member in a second mode in which the intermediate transfer member contacts the first photosensitive drum and separates from the second photosensitive drum,
• wherein, in a case where a black monochrome image is formed on the sheet in the first mode, the controller controls, based on data related to a load torque of the motor, a target rotation speed of the second photosensitive drum for mixed-color image forming.