Yup, cars and music, very much alike. And that's probably the best way to explain your passion to non enthusiast freinds. Seriously, try it next time, it works!
If one takes pleasure in driving and appreciating a car in the same way one takes pleasure in playing and listening to music, then it could be argued that cars are like songs. There are the seasonal Top 40 hits, pop cars aimed at the general public which enjoy a period of popularity before aging into oblivion, there are the eternal classics which are as good today as they were when new, and there are the turds that become cool after a well done remix or cover. There are the legends which changed the way things were done and there are those hits whose bands have long broken up but still live in our hearts. There are even the obscure pieces and songs you probably never heard of.
Much in the same way in which there is a non discerning public to music who will listen to whatever's on the radio at the moment, there's a non discerning public to cars, who will drive whatever's on sale right now.
Much in the same way in which there is a portion of music listeners who only care about the image brought on by a specific musical style, there are automotive posers, who will brag and showoff that their car is faster/bigger/more expensive than everyone else's without, in fact, knowing squat about how automobiles work or what makes a good one.
Much in the same way in which you can listen to something written in the 60's and like it, you can drive something made in the 60's and enjoy it because in cars, very much like in music, technical advances don't mean a newer car is subjectively better, just that it's different.
Much in the same way that there are incredible stories, sometimes filled with transgression, depression and substance abuse, sorrounding the creation of legendary tracks and albums, there are incredible stories, sometimes filled with transgression, danger and ingenuity sorrounding the creation of legendary cars or runnings of legendary races.
In all these years as a gearhead, I've had people ask me why I like one of the grand evils of modern society, I've had armchair experts telling me I can't be a car enthusiast if I don't drive some form of hyperexpensive supercar, I've had people trying to convince me that classic cars are a fad and that they could never actually be better than a new car and I've even had people ask me why I drive what I drive when it breaks down every once in a while. I hope this is explaining enough, even though I didn't say anything at all. Loving cars, very much like loving music, can't be explained, but is it really that hard to understand?