I'm surprisingly uneducated when it comes to machine heads, I know nothing about them, however, I have stock grovers on an epiphone and one of the keys is very slow when responding to turns, is there a way to change this on grovers or is it going to need replaced? It generally stays in tune, but it's a pain to tune the string when it takes a full turn to get the slightest reaction.
Different machine heads have different ratios. I think on Grovers it's 18:1. That means you need to turn the key 18 times to get one full revolution of the post. Higher ratio means you have to turn it more, but you can also tune more precisely. If it bothers you that much, you can replace them with different ones.