Rival eTap AXS flat mount calipers work with 140mm and 160mm rotors with a standard flat brake mount. Certain frames are made to work with flat mount calipers and 180mm rotors-see your frame manufacturer to be sure which brake mount type your frame requires.
See the "Recommended Road Rotor Size and Brake Pad Chart" in the eTap AXS Systems Manual for recommendations based on riding style and system weight.