Late in the book, Pirsig brings up the Greek concept of "arete" (pronounced ar-ruh-TAY, with the accent on the last syllable). There is no direct translation of this word to English, but it is similar to the concepts of virtue and excellence.
In the early Olympics, the champions were not specialist in a single sport or activity. Running faster than everyone else was simply not enough to be declared an Olympic champion. They had to excel in different sports, but also have to be masters of music, art, poetry, philosophy and pretty much every thing else. This is an example of arete applied in early Greek culture.
In The Art of Manliness Manovations, Brett and Kate McKay put it this way:
"For the ancient Greeks, the ideal life was one filled with eudaimonia. What's eudaimonia? Translators and philosophers have given different definitions for it, but the best way to describe eudaimonia is the attainment of "flourishing", through, as Aristoltle put it, "doing and living well". Greek philosophers believed that eudaimonia was achieved through the practice of arete. Translated as "virtue", arete is better understood as excellence and was sometimes use interchangeably with andreia, or "manliness". The man of arete maximized his full potential in body, mind and soul; despite setbacks and challenges, he effectively used his abilities to fulfill his life's purpose and achieve a real and lasting legacy. Thus for the ancient Greeks, manliness meant being the best man you could be."
(Note that I read and think of this as being "gender neutral", meaning the concept applies equally whether it be man or woman.)
Pirsig's idea of quality goes toward something constantly being the best that it can be, yet constantly improving, striving to be better.
So, Kim, your idea that "quality is relative" really applies to this, as quality is constantly improving, constantly getting better than it was before.