Truss Rod - Application

Application

When the truss rod is loosened (i.e., moved towards the guitar's body), it allows the neck to bend slightly in response to the tension of the strings. Similarly, when tightened (i.e. moved towards the guitar's headstock) the truss rod straightens the neck by resisting the tension of the strings.

It is desirable for a guitar neck to have a slight relief in order that reasonably low action be achieved in the high fretboard positions, while at the same time, the strings ring clearly in the low positions. Improved action in the high fret positions also allows for more accurate intonation to be achieved with less compensation at the bridge.

Relief achieved through the truss rod combines with the height of the bridge to affect the playability of the instrument. The two should be adjusted in tandem. Too much relief contributes to a neck that feels stiff and lifeless, while too little feels floppy, slow and imprecise.

Truss rods are required for instruments with steel (high tension) strings. Without a truss rod, the guitar's wooden neck would gradually warp (i.e. bend) beyond repair due to applied high tension. Such devices are not normally needed on instruments with lower tension strings, such as the classical guitar which uses nylon (previously catgut) strings.

Truss rods also allow the instrument neck to be made from less rigid materials, such as cheaper grade of wood, or man-made composites, without which the neck would not be able to properly handle the string tension. The neck can also be made thinner, which can improve playability. In fact, the possibility of selecting cheaper materials is specifically touted in the 1923 patent as an advantage of the truss rod. Prior to the introduction of truss rods, the neck would have been made of a very rigid wood, and relief was achieved by planing the fingerboard: more expensive material, and more demanding construction technique.