Comments on the paper "Terminal retrograde turn of rolling rings"
  Mir Abbas Jalali et al. [Phys. Rev. E 92, 032913(2015)] explained the retrograde turn of rings by aerodynamic phenomena due to the presence of a central hole in the ring as opposed to a disk. The results of our experiments suggest that the drag torque is not the main reason for the retrograde turn of the rings, and the results of theoretical research have shown that such a motion is possible for both the ring and the disk in the case of rolling without slipping. 
Alexey V. Borisov, Alexander A. Kilin, Yury L. Karavaev
physics.class-ph