Have descended Kitt Peak near Tucson, AZ.
About 8.000 ft elevation, 6 to 7% grade, twisting turns for 11 miles on our tandem bike back in 1978.
Utilizing front and rear Mafac canti brakes. No third brake. No tire issues.
Did have to stop halfway down as fingers were cramping from constant on/off braking. Felt the alloy rims; they were warm but by no means hot.
Continued descent without interruptions.
Justy our experience.