When decreasing string gauge on a bass guitar, will I need to adjust the truss rod?

Question

I'm planning to make some changes to my bass guitar. I'd like to:

• Moving from heavy to medium strings
• From flatwound to roundwound strings
• Lower the action

Obviously, the guitar will need a new setup: The lower-gauge strings will affect the intonation, put less tension on the neck, and possibly require me to move the pickups closer even if I do lower the action. (I'm planning to open it up and clean the noisy pots while I'm at it, much in the same way I cleaned these faders.)

This instrument (a Peavey T-40) is amazingly easy to work on, and I've set it's action and intonation on this guitar in the past. (It's the same guitar I mentioned in this question.)

Pictures:

My question: Are adjustments beyond setting the action and intonation generally needed when making these string swaps? (If so, I'll likely bring this to a shop.) Does doing a setup like this often require adjusting the truss rod? That's something I'd prefer to avoid doing on my own, as I've heard of people damaging the neck of a guitar by doing it improperly.

(I'd not be quite as concerned on a regular guitar, where the string tension is lower.)

What do I need to look out for when doing this?

Answer 1

The change in tension is likely to cause a difference in the bowing of the neck, and adjusting the truss rod is the way to fix it.

However, I don't think you should be too scared of tackling it yourself.

Fit the new strings. Play. If everything feels fine, stop worrying and keep playing.

If you feel there are problems with the action high up the fretboard, or there are issues with intonation, consider doing some adjusting.

As long as you make the adjustments a quarter turn at a time, and measure the action at the 12th fret accurately between each turn, you're not at risk of damaging the instrument.

(* I take no responsibility for any damage to your instrument :D )

Answer 2

Changing the gauge of string will change the tension which affects everything in my opinion. I've been playing for 20 years and for the first 16 of those I thought I was doing quite well setting up my instruments action, truss rod, etc by carefully following instructions found in books, magazines, and then eventually the internet. I was wrong.

Then I stopped trying to be what I wasn't - a bass/guitar tech. I took my fretless jazz bass to a locally recommended guy and that $700 bass, which played decently before, played like what I would imagine a $3000 bass would play like. It was heaven.

Short story long - if you want it done right take it to someone who knows what they're doing. If you have a 2nd instrument, practice on that one and try to emulate the work done on your professionally setup instrument.

Answer 3

I think it will have a lot less impact than you think. I'd suggest swapping out the strings and playing on it a little bit before making any changes at all, in fact. By the way, once you go to roundwound strings you will never go back.