Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
dismount [dɪsˈmaunt] vi (from horse) спе́шиваться (спе́шиться perf) (from bicycle) слеза́ть (слезть*perf)
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.