Last Updated on September 5, 2023 by Teemu Suomala
Author: Teemu Suomala
Guitar terms are one thing that can make beginners shiver…and a truss rod is one extremely scary thing…right?
Let me tell you…in basic guitar terminology, there’s nothing you can’t understand easily.
One of these basic guitar terms is a truss rod. A backbone of a guitar. It plays a huge role in your guitar, supporting the neck and allowing you to adjust the neck if needed. And in just a couple of minutes, you know exactly what a truss rod is, what it does, and how to adjust your truss rod.
Let’s get things related to the guitar truss rod sorted out!
What is A Truss Rod on Guitar?
A truss rod is a metal rod that is installed in the middle of the neck of the guitar to add support and keep the neck from bending under the pressure of the strings. Most modern guitars employ an adjustable truss rod to adjust the neck relief, while some older guitars have a truss rod that is not adjustable (also called a steel reinforcement bar). The majority of truss rods in mass produced instruments today are cost-effective single-action (or compression style) truss rods.
What is A Dual-Action Truss Rod?
A dual-action truss rod allows you to adjust the neck in both directions: forward and backward. This way you can either back- or forward-bow the neck. This type of truss rod is also commonly referred to as a two-way or double-action truss rod and are becoming more popular due to their superiority.
In terms of construction, a modern dual-action truss rod usually has two metal rods running inside the neck. By allowing one rod to induce pressure against the other through threaded anchors at each end, the whole unit can be adjusted to flex in one direction or the other.
Another type of common double-acting truss rod is the Bi-Flex truss rod system. The Bi-Flex truss rod, common to Fender instruments, is essentially a single-action truss rod that, through the use of ingenious blocking, acts as a two-way truss rod.
If your guitar has the familiar walnut “skunk stripe” insert on the back of the neck, you probably have a Bi-Flex truss rod.
But, there are 2 types of dual-action truss rods out there…so let’s get things straight!
Historically speaking, yes, the term “dual-action” refers to the original two-piece construction designed to improve the adjustability of the traditional single-action truss rod.
The original dual-action truss rod still has 2 rods that are inserted into the same block from the adjustment end and welded together at the other end. With this kind of dual-action truss rod, only one rod bends and can’t correct the back bow because it essentially acts as a single-action type of truss rod.
Additionally, the use of the this dual-action truss rod is not very common nowadays. Though it is heavier, this original kind of dual-action truss rod is still more stable and stronger than a single-action truss rod.
The modern dual-action 2-way truss rod has 2 rods, both inserted into the threaded blocks from both ends. This system is by far the most common nowadays. It’s lighter than its predecessor, takes up less space in the neck and can bow the neck in both directions.
This LuthierTalk thread reveals you more about about different truss rod types and also shows images of original style dual action truss rod and the improved dual action 2-way truss rod.
For the purposes of the rest of this article we’ll consider the terms “dual-action” and “dual-action 2-way” truss rods to be one and the same in reference to the modern version.
Main Differences Between Single-Action and Dual-Action Truss Rod
With a modern dual-action truss rod, you can either back-bow the neck by tightening it or forward-bow the neck by loosening it. With a single-action truss rod, you can only back-bow the neck by tightening it, and by loosening it, you can only make it go far as the string tension pulls it to the forward bow direction, but you can’t any forward bow to that.
The dual-action truss rod is handy if the neck of your guitar is naturally (or because of humidity or lack of it) back bowed and the string tension is not enough to pull the neck straight to allow fret buzz-free playing. You can just forward bow the neck with a dual-action truss rod and you are ready to go.
Another upside of all the dual-action truss rods is the fact that it better supports the guitar’s neck and keeps the neck more stable than a single-action truss rod.
| Steel Reinforcement Bar (Non-Adjustable Truss Rod) | Single-Action Truss Rod | Modern Dual-Action Truss Rod | |
| Supports The Neck | Yes | Yes | Yes |
| Can Correct Forward Bow (Neck Relief) | No | Yes | Yes |
| Really Stable | No | No | Yes |
| Heavy | No | No | Yes |
| Can Correct Back Bow | No | No | Yes |
Guitar Truss Rod Construction
A small channel (truss rod channel) is carved in the middle of the neck guitar’s neck. Here the truss rod is installed and the adjustment (nut or bolt) end of a truss rod is usually placed to the soundhole end of the neck with acoustic guitar, and to the headstock end of the neck with electric guitars.
Dual action truss rods should always be installed by the adjustment nut side at the bottom.
Check our full guide to acoustic guitar anatomy here and electric guitar anatomy here.
How Guitar Truss Rod Works?
The Truss rod works as a support for the guitar neck because the neck is put under a lot of pressure by the strings. Most truss rods also work as a way for the guitarist or luthier to adjust necks forward or backward bow (curve). Truss rod adjustment is one of the key things every guitarist should learn to handle.
What Does Adjusting A Truss Rod on The Guitar Do?
Adjusting a single-action truss rod of a guitar decreases the neck relief that is caused by the guitar’s strings and humidity or lack of it. Adjusting a two-way truss rod either decreases or increases the neck relief caused by the same things, the pressure of the guitar strings and humidity or lack of it. Truss rod adjusting also plays a role in action adjustments.
How To Adjust A Truss Rod of A Guitar?
Let’s tackle this: How To Adjust Your Truss Rod…
- Check if your guitar’s truss rod even needs adjustments (see the “How to Know if Your Guitar Needs Truss Rod Adjustments?” section below for more info) and in which way you should turn it.
- Then check if your trust rod has a socket head screw (also called truss rod screw) or nut (also called truss rod nut) for the truss rod adjustment.
- Get the correct tool. Common hex key sizes are 4mm and 5mm for most imports, 1/8″ hex key for American made-Fender, 5/15″ box wrench for American-made Gibson guitars, 1/4″ socket wrench for Taylor acoustics, plus a few more variations depending on manufacturer. For example, the heel access spoke wheel truss rod adjuster common to Ernie Ball Music Man guitars can be adjusted with hex keys or with steel rods in general.
- Turn the truss rod screw or truss rod nut in the right direction (see correct directions below), and check if it made the neck bow tilt in the right direction. Use a ruler or tap test to find out if the neck’s bow got better (see the “How to Know if Your Guitar Needs Truss Rod Adjustments?” section for more info).
- Tune the guitar
- Give it time to settle. After each adjustment, give the guitar time to adjust to the change in pressure. Changes in neck relief may take hours or even days to fully manifest. Monitor the guitar’s playability over time to determine if additional adjustments are necessary.
- If things got better, rock on!
Guitar Truss Rod Directions
Righty tighty and lefty loosey, awesome memory trick I learned from SteveMac’s Dan Erlewine. When you tighten the truss rod by turning it to the right, you add a back bow to the neck. When you loosen the truss rod by turning it to the left, you decrease the back bow. With a dual-action 2-way truss rod, you can also add a forward bow by turning the truss rod to the left.
Truss rod adjustments are the easiest way to adjust action of an acoustic guitar.
How to Know if Your Guitar Needs Truss Rod Adjustments?
The best way is to use a long ruler to check if the neck of your guitar needs truss rod adjustments. If there’s a gap somewhere between the ruler and a fret, that means your truss rod needs adjusting. Another thing that can cause this is uneven frets.
If you don’t have a long ruler (I recommend buying one), you can also press your string down from the 1st fret and from the 15th fret(this with your pinky), and then use your hand pressing the 15th fret to press frets directly from the fret wire towards the neck of the guitar. If you can feel that there’s a gap between the fret and string, your guitar’s truss rod most likely needs some adjusting. This method of testing neck relief is also referred to as the “tap test“.
FAQ
Do All Guitars Have a Truss Rod?
No, all guitars don’t have truss rods. Classical guitars oftentimes don’t have a truss rod since the nylon strings don’t put so much pressure on the neck. Nowadays classical guitars with adjustable truss rods are becoming more popular since adjusting the neck allows players to achieve the perfect playing set up for them.
Some older steel-string acoustic and electric guitars don’t have truss rods either (rare) or they might have a truss rod that is non-adjustable. For example, many older vintage Martin acoustic guitars made after 1934 had a non-adjustable “T rod” installed to help stiffen the neck against warping.
How to Tell if a Guitar Has a Truss Rod?
The truss rod access is what you should look for first.
Usually, you can check the headstock of the guitar, the area right after the neck and nut, to see if there is a hole where the truss rod access is located, or with some guitars, there’s a plate covering the truss rod. The headstock of the guitar is a common place for electric guitars to have a truss rod adjusting socket head screw, bolt, or nut.
Some electric guitars have a truss rod that can be adjusted from the heel of the neck. This is referred to as Truss Rod With Heel Access Spoke Wheel. These can be adjusted with hex keys or some with small steel rods in general.
With most acoustic guitars, a truss rod adjustment socket screw or nut is installed at the end of the neck, inside the soundhole. This way, the truss rod can be easily accessed through the soundhole.
Should Guitar Neck Be Perfectly Straight?
The guitar’s neck should be as straight as possible, although some guitars can’t handle a completely straight neck and maintain a correct intonation at the same time. If this is the case, a slight forward bow of the neck can be accepted. But always try to make your guitar’s neck as straight as possible.
How Do Truss Rods Effect The Guitar?
The truss rod allows the neck of the guitar to withstand the pressure it is put under by the guitar strings. The Truss rod also adds a little bit of weight to the neck of the guitar, and if you hit the guitar with a dual-action truss rod, it gets even a bit more heavier.
Do Electric Guitars Have A Truss Rod?
Yes, electric guitars almost always have a truss rod. Some older electric guitars might have a truss rod that is non-adjustable.
Do Acoustic Guitars Have A Truss Rod?
Steel-string acoustic guitars almost always have a truss rod. Some old acoustic guitars have a truss rod that is non-adjustable. Also, some of the cheap steel-string acoustic guitars might not have a truss rod at all.
Do Classical Guitars Have A Truss Rod?
As mentioned, most traditional classical guitars don’t have a truss rod. The reason for this is that the nylon strings don’t usually add so much pressure that the neck would start to suffer from neck relief.
What is A Guitar Truss Rod Cover?
A truss rod cover is usually just a plate installed to cover the truss rod and the truss rod hole. The plate is there to make the guitar look better, so it’s pretty much for decorative purposes only.
What Forward Bow of The Guitar Neck Does?
Neck relief/forward bow of the neck means that the guitar’s neck is bowed forward. So when we look at the guitar from the side, the headstock starts to tilt forward. When this happens, turn the truss rod nut clockwise (right, tighten) in order the straighten the neck and get rid of neck relief.
What Backward Bow of The Guitar Neck Does?
A back-bowed neck means that the guitar’s neck is bowed backward. When we look at the guitar from the side, the headstock starts to tilt backward. To fix this, turn the truss rod nut anticlockwise (left, loosen) in order the straighten the neck and get rid of neck relief.
If your guitar’s neck just naturally bows back, the string pressure is not enough to straighten the neck, and your guitar is not equipped with a double-action truss rod, then things get tricky. If this is the case for you, I recommend visiting an experienced luthier.
Conclusion on Guitar Truss Rods
You probably agree with me now…understanding basic guitar terms, truss rods included, is far from an impossible task. You now know how the truss rod works, how to adjust your truss rod, and how it affects the guitar. If you have any questions about truss rods or anything related to guitars, just ask in the comments!
I hope that truss rod adjustment is no longer one of those things that make you shiver… Keep rocking (with the correct amount of neck relief)!
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I really like reading through a post that can make men and women think. Also, thank you for allowing me to comment!
This post is a game-changer, thank you!