Helpful hint from your friendly neighborhood word-slinger: “further” and “farther” are not actually interchangeable like say “literally” and “figuratively.”
Use “farther” when you are discussing an actual, literal (in the literal sense of the word literal) distance between two things.
Use “further” when you are talking about a metaphorical or figurative (in the imagined sense of the word “literally”) distance between two things.
Nothing could be further from the truth than the idea that I’m an overindulgent dad, so no, I’m not stopping for another pee break until we get farther down the road.
Furthermore, when you just cannot decide if you’re speaking literally literally or figuratively literally, you should err on the side of figuratively literally and go with “further.”
Better to be safe than sorry when you’re having to clean the leather seats.
And for the record, no, “literally” and “figuratively” are not interchangeable either. Grammar serves humor; the reverse is never true.
Until next time . . .