Dry weight

Dry weight: The weight of a vehicle without any fuel, oil or coolant.

Drive shaft or Propeller shaft

Drive shaft or Propeller shaft: Assembly of a shaft or tube with two universal joints, used to transmit power from the transmission to the drive axle. Also called propeller shaft.

Drive line

Drive line: The entire system drive shaft including universal joints, slip yokes and flanges between the transmission and axle(s).


Drive-by-wire: Any driving system which is controlled by electronic responses sent to a control module.

Drag link

Drag link: The member connecting the steering arm to the idler arm of the steering system.

Double declutching

Double declutching: Literally meaning, 'disengaging the clutch two times', the procedure is used in case of gear box without synchroniser, to gear down, i.e., to obtain lower gear.

Divided wheel

Divided wheel: A wheel constructed in two parts, which when securely fastened together, combine to form a rim having two fixed flanges.


Dive: Nose-down pitching motion of a vehicle. Dive occurs on account of weight transmission from rear to front during braking.

Directional tyre

Directional tyre: A tyre having tread grooves swipe away in a backward direction from the center of the tread face and is meant to rotate in only one direction, giving improved dry and wet traction in that direction. Arrows are stamped on both sidewalls of the tyre to indicate the direction of rotation.

Directional stability

Directional stability: Ability of a vehicle to travel straight ahead with minimum driver control.

Dimmer switch

Dimmer switch: A device to decrease or increase the brightness of the headlights by switching from high beam to low beam and vice versa.

Dimming mirror

Dimming mirror: A rear-view mirror located above the windshield which can be switched to reduce the glare from the headlights of a vehicle approaching from behind. These may be self-activating type or manual type to be engaged by operating a lever on the mirror.


Differential: The arrangement to ensure equal speeds of the inner and the outer wheels of an axle while taking turns. In an ordinary differential, the torque transmitted is always equally divided between the two wheels on the axle, even when their speeds are different.

Diagnostic trouble code

Diagnostic trouble code: A numerical identifier for a fault condition detected by the on-board diagnostic system.

Diagnostic testing

Diagnostic testing: Analysis of various functions of the components and systems of a vehicle to determine if they are operating properly or have recorded faults which have to be rectified.