DAMPING The process that absorbs the energy of an impact transmitted through a suspension system. It controls the speed at which any form of suspension responds to uneven terrain.
DERAILLEUR GEARS A system that shifts the chain between sprockets on the rear wheel (rear derailleur) and between chainrings attached to cranks (front derailleur); it allows multiple gearing on bikes. See also Mech.
DOWN TUBE The frame tube that joins the bottom-bracket shell to the head tube.
DRIVETRAIN The assembly of pedals, chainset, chain, and sprockets that drives the bike forwards by transmitting leg power into wheel rotation. See also Transmission.
DROP-OUT A slotted plate at the end of the fork legs and stays, into which the axle of a wheel is attached.
EXPANDER BOLT A bolt that draws up a truncated cone or triangle of metal inside a metal tube in order to wedge the tube in place. Commonly found inside the stem of a threaded headset.
FREEHUB A mechanism, part of the hub, that allows the rear wheel to rotate while the pedals remain stationary.
FREEWHEEL A mechanism that does the same job as a freehub but can be screwed on or off the hub.
GEAR An expression of the chainring and sprocket combination, linked by the chain, that propels the bike.
GEAR-SHIFTER The control mechanism, usually on the handlebar, used to initiate gear-shifts.
GRUB SCREW A headless, threaded bolt that has a single diameter throughout its length.