  In ring-ring colliders, the collision frequency determines the bunch
structures, e.g. the time between the bunches in both rings should be
identical. Because of relatively low relativistic speed of the hadron beam in
sub-TeV hadron-hadron- and electron-ions-colliders, scanning the hadron beam's
energy would require either a change in the circumference of one of the rings,
or a switching of the bunch (harmonic) number in a ring. The later would cause
so-called 'gear-changing', i.e. the change of the colliding bunches turn by
turn. In this article, we study the difficulties in beam dynamics in this
'gear-changing' scheme.
