What does HRD stand for? August 31, 2016 13:18 Hydraulic Road Disc. Related articles Do eTap® HRD brakes use DOT fluid or mineral oil? What is the difference in weight between the mechanical rim brake version of SRAM RED eTap 2x11 and SRAM RED® eTap® HRD 2x11? What are the main differences between RED eTap AXS™ and Force eTap AXS™? Why did SRAM choose DOT 5.1 over mineral oil? What is the bed-in procedure (brake preparation)? Comments 0 comments Article is closed for comments.