unsteadiness

noun

1. (countable, uncountable)The quality of being unsteady.

   “The Marsh rebuilding, with the higher-pitched and larger boiler and new standard boiler mountings, completely altered the appearance of the engine, which in its last guise was a very handsome machine; but unsteadiness in running at speeds over 50 m.p.h. resulted in no further such conversions being made.”