It’s a pretty common problem: you have an entry level or budget guitar and you’re pretty happy with it for now – maybe you’ve upgraded the pickups or you’ve put a few stickers on the body to cover up some dings and scratches. You’re not ready to buy a new guitar yet, but you’re starting to reach the limitations of what your first axe and do for you, and as your ear gets more and more accustomed to how the guitar should sound, you’re noticing that it’s going out of tune a lot. And it makes sense to think the tuners are the cause of the problem.

That might not necessarily be the case though. Don’t get me wrong: it could be. But your first option when trying to solve a tuning problem should always be to install a new set of strings. Give them the ‘ol stretch test –  hold each one down at the first fret and carefully stretch it a little, retune and repeat – and then if they still go out of tune, it’s probably not the strings. But it still might not be the tuners.
I speak from personal experience. When I was about 14 I got fed up with the tuning problems I kept running into with my cheapie Stratocaster copy, so my dad and I installed a new set of tuners. Apart from feeling nicer to turn, there was no change at all in my tuning stability. At first I thought it was because of the guitar’s vibrato bridge, but when I screwed it right to the top so it couldn’t move, the tuning woes continued.
I later discovered that the issue was with a poorly cut nut (If you’re relatively new to guitar, this is the part that the strings pass over before getting to the headstock). Because the strings come into contact with the nut before getting to the tuners, it’s a prime candidate for tuning problems. It can be so tight or roughly cut that it can ‘pinch’ the strings, and that tension can be released when you bend a note – and this will throw you out of tune. It can be so loose that it doesn’t effectively hold the string in place – and this will throw you out of tune.

If it ain’t broke, don’t fix it. Unless you want something that’s a cooler color.

If this is what’s causing the problem, there’s still something you can do before taking the drastic step of having the nut replaced: use a purpose-made lubricant (even a graphite pencil works in an emergency) to lubricate the nut and any other part that the string passes over: i.e.: the bridge saddles and ‘string trees.’ A few quick scribbles over these parts with a graphite pencil or a few dabs of a product like Big Bends Nut Sauce will help the strings to glide over these contact points. And then, if the tuning problems still persist, you either need to have a tech inspect the nut to either:
* Recommend a different string gauge
* File the nut slots a bit
or
* Replace the nut.
And then, if none of these things solve your tuning problems, it could be time to change your tuners.
Of course, there are other great reasons to change your tuners: cosmetics (some just look better than others, and anything that makes you feel better about your guitar is a good thing), or because you’d prefer a different gear ratio, or because you’d prefer locking tuners, or string-cutting tuners. And all of these are valid reasons, and lots of fun too! Just make sure that whatever reason you’re changing tuners for, it’s the right one.
Have you changed tuners? What kind do you prefer?