Why did I have to TIGHTEN my truss rod this spring?

I’m an old hand at truss rod adjustments - hell, I can tweak it while I’m strapped into the guitar!

In the past, with other acoustics, I’ve had to tighten it in the fall (beginning of heating season here in Nova Scotia), and loosen in the spring when the heat goes off.

It was always my understanding that this was because of humidity - central heating dried out the wood, and shortened the neck - requiring a truss rod tweak to maintain proper relief.

But this spring, with my new Martin, I had to TIGHTEN the truss rod, and I don’t understand why.

It’s an entry level Martin, with a solid spruce top, but a composite body. It also has a bi-flex truss rod. Could these be factors?

It’s not a problem. It just bothers me that I don’t understand why this is happening.

My guess would be that it is new and hasn’t yet settled into the environmental baseline. Only a guess.

I should have been clearer – the guitar is about 15 months old – this was it’s second heating season.

You know , I’ve played guitar for many years and I’ve never once adjusted my truss rod ! I’m kind of scared to do it. Not sure I’ve needed to , or maybe just not aware what I’m looking for

Truss rods are supposed to be adjusted, they are just another mechanical part of the guitar like the tuners.

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Lewis, maybe you’ve never needed to - if your guitar is very solid and stable, or is stored in constant humidity.

I mainly tweak mine to lower the action. I know to do this when I start having trouble fretting chords - particularly the “Justin A” (the 213 fingering that Justin teaches).

It’s not difficult…much easier than changing strings, IMO. I think there are many YouTube videos that show you how.

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I would like to correct a misconception.

Relief and action are not the same and adjusting relief by adjusting the truss rod should not be done in order to adjust the action.

On an acoustic guitar, relief is measured at the 6th fret on the low E string with it fretted at 1 and 12. Generally, the relief should be in the range of 1/2 mm or less, but there should be a hair of relief. Slightly less than the thickness of a business card perhaps.

This would not be enough to meaningfully adjust to lower action, unless it was set with too much relief in the first place or you are getting the concept wrong and putting the neck into back bow.

First tune the strings. Then set the correct relief with the truss rod. Then make sure the nut is correctly cut. Then, and only then, adjust the action by adjusting the saddle.


Joshua - yeah I was sloppy with my terminology - I should have said relief.

You define relief very clearly, but what is the definition of action?

Action is the height of each string (from the bottom edge of the string) to the top of the 12th fret. Some people set it with a capo in the first fret, but you don’t need to as long as you are consistent.

Higher action is a bit harder to fret, but let’s you be more aggressive in your playing without the vibration of the string hitting the frets and causing buzz.

Lower action makes the fretting easier and faster, at the risk of buzzing with improper setups or more aggressive playing.

Electric guitars can have lower action because the strings don’t need to vibrate as hard (high amplitude) to make sound.


Hmm, I think relief is one element of action. As in it affects action, rather than being something different.

The last few months we’ve had some unusual weather - extreme wet to very dry. Noticed the difference in my acoustic but electric didn’t change much at all.