unsprung

adjective3

1. •
   Not sprung.
2. •
   Not supported by the suspension of a vehicle.

   • The locomotive is carried on two six-wheel bogies, the outer axles of each bogie being driven by series type d.c. motors, completely suspended to reduce the unsprung weight to a minimum. — 1947
3. •
   Not fitted with springs; lacking springs.

   • The Winchburgh Shale Line is of 2 ft. 6 in. gauge. The surface trucks or tubs are cuboidal metal boxes mounted on unsprung four-wheeled chassis. — 1958