Chin Hang Rings vs. Bar

Biomechanically, is the chin hang on rings more difficult than the bar?

The bar seems to force a greater rotation of the radius and puts greater pressure on the brachioradialus, but the rings seem to require greater flexion of the lats and biceps.

Are you talking about RC/PE6, or dead hangs? If it's the former, then they are to be done on a bar.

RC/PE6, chin hangs.  And I'm not asking if they're supposed to be done on a bar according to the program, but the biomechanical rationale behind choosing the bar over the rings.

In supination biceps brachii and brachioradialis are also contributing to arm flexion. The chin hang is an all around strengthener for elbow flexion and grip.

That's what I discovered.  My brachioradialus is sore all around from 5x60s ring support and 5x60s handstand, so the soreness in the chin hang emphasized its importance in elbow flexion.