Everything you need to know about the truss rod.

  • Posted on
  • By Erik Bogaards
  • Posted in truss rod
  • 2
Everything you need to know about the truss rod.

It is a hidden part in lots of guitars: the truss rod. As this little piece of metal can help you to perfectly set up your acoustic guitar, we decided to bring the truss rod to the surface.


Where's the truss rod?


Sometimes it's nowhere, because not all guitars have a truss rod. You'll read more about that later. But if there is a truss rod in your guitar, it's in the neck. It is a metal pen that should make sure that your guitar neck can withstand the continuous string tension. A guitar neck is made of wood, so if you pull it long and hard enough, sooner or later a bow will come in.  A simple and somewhat exaggerated sketch of the side of a guitar it looks like this:





A guitar neck can therefore use an extra support in the back to help resist that string tension. There are several ways to do this. Sometimes by strengthening the heel with harder, tropical wood. But a square or T-shaped metal pen in a milled slot in the neck, directly below the fretboard, quickly became the standard solution.


Source: Martin Guitars


Is a truss rod adjustable?


Such a metal pen provided more firmness, but there were also some disadvantages. Wood can shrink and expand more than metal causing some wiggle room or friction. You can solve that by making the metal pen move slightly with or against the wood. In as early as 1923, Gibson commissioned a patent for the adjustable truss rod.



With such an adjustable truss rod you can change the curvature or relief of the neck at any time, by turning the metal pen a little tighter or looser. Nowadays there are even dual action or two way truss rods. They move in two directions, so you can determine the curvature of the neck even more  precisely. For some extra strength and less weight, sometimes they are even made of  titanium!


Does every guitar need a truss rod?


Nowadays, such an adjustable piece of metal in the neck is simply the standard. Even a traditional guitar builder like Martin has been putting adjustable truss rods in most models since 1985. This makes it seem as if a truss rod is now an indispensable part of a guitar. But it's not.  Guitars are also fine without! Just listen to this  Vivi-Tone.



And how about this Epiphone FT37. More than 80 years ago it looked like this on a poster...



And now it sounds like this. Without an adjustable truss rod!



How is that possible? Fellow Maarten Dispa has played dozens of guitars without  truss rods. ,,Just look at classic guitars, most of them are without. And western guitars without a truss rod are just reinforced in a different way. Gibson, for example, made some full mahogany J45’s in 1944 that had an ebony reinforcement. Metal was scarce at the time because of the war, but thanks to that extra wood they are fantastic guitars! If you take good care of such a guitar,you don't need a truss rod at all."


But doesn't a truss  rod have any advantages at all?  Maarten: ,,Definitely! It can be very useful, for example, if you play guitars in a different tuning , or if you start playing with strings with a different gauge. Then the tension on the neck changes and you can easily adjust the guitar to it. In a set-up, we always take a good look at it. But really necessary? No, it's actually not. In the most ideal case, a neck just always stays as stable as possible and there are several good and smart solutions for that. With extra wood, for example, but carbon is also possible. Laminated necks of several pieces of wood, are generally also much stronger. So who knows… in 20 years we might be selling more super-stable guitars without a truss rod."


How can I adjust the truss rod?


First, you have to find the screw to adjust the truss rod, because it is often hidden. For some brands (including  Taylor, PRS and Gibson) it is under a small plate on the head stock.



With other brands (i.e. Martin, Lowden, Collings, Santa Cruz) the access is at the end of the neck and you can reach it through the sound hole.



Srouce: Collings


Make sure you use the right tools. There is not one truss rod key or wrench that fits all guitars. Usually you get the right wrench when you buy a guitar and this prevents unnecessary damage. Are you not sure about what tools to use? Please check with the builder/luthier or contact us.


Which way should I turn the truss rod?


In this video from Acoustic Life, Tony Polecastro explains what a truss rod does and how to play with it a bit. 



Do you want more of a bow in the neck? Then you loosen the truss rod.  


Left = Loose.


Source: guitaranswerguy.com


  • Usually you do this when the strings rattle against the fretboard.


Do you want less of a bow in the neck? Then you tighten the truss  rod. 


Right = Tight


Source: Guitaranswerguy.com


  • Usually you do this to make the distance between the strings and the fretboard a bit smaller (also called: lower action), in order to make your guitar play a little easier.


This rule: Left = Looses and Right =  tight, goes for both trussrods with a screw-end in the sound hole and in the head stock, as long as you look over the neck to determine the direction.


With a screw in the sound hole, Left = loose looks like this:



Source: Lakewood


In the case of a screw in the headstock, The Left = loose looks like this:


Source: Taylor


When adjusting the truss  rod, you look for the perfect distance from the strings to the fretboard. That balance is slightly different for each instrument and each player, but in general most acoustic guitars work best with a very slight bow in the neck. This allows the strings to vibrate without rattling against the frets also known as buzzing.


Adjusting the truss rod yourself or having it done?


In short, you can slightly adjust the curvature of the neck by turning the truss rod tighter or looser. This way you can make your guitar a little easier to play. You can also improve intonation slightly or solve problems with buzzing strings. That sounds like a kind of miracle and if you have to believe the internet,it seems like a breeze.


Still, we do not want to scare, but warn you, because we sometimes see things go wrong.


First, because some people turn the truss rod too far. Then rod can get too tight and hence you can seriously damage a guitar. It is good to know that the noticeable changes of less than a quarter turn of the truss rod are subtle, because sometimes a guitar takes more than a day to adjust to such a slight turn. If you don't wait and keep turning the rod, you turn too far and find out about real consequences until days later. Others are too cautious. Turning the rod tighter  with the full tension on the strings, can also cause problems with the bridge.


And finally, the very slight relief of the neck is just part of  the perfect set up of an acoustic guitar. The height of the nut,  the bridge and the frets are just as important. With a professional set up, a  guitar builder takes care of that right away. So yes: you can play with the truss rod yourself. But always be  careful. Do you doubt? The luthiers in our workplace have experience in adjusting almost all guitar brands. Acoustic and electric! So feel free to get in touch.




  1. Maarten Dispa Maarten Dispa

    I believe they started it in 2006 but didn't reach full capacity till 2008. The chance is big that it's not a two-way truss rod.

  2. James Morrison James Morrison

    Do you know when Martin went to two way adjustable truss rods? I have a 2006 HD-28. I tried to loosen the truss rod turning it counter clockwise. When I turned it the nut unscrewed off the end of the rod. I took this as a sign that it was a one way truss rod.

Leave a comment
* Your email address will not be published