Amount of hair proportionate to the rocking.
Rock 'n' roll has had a long history of long/huge hair that somehow got lost in the 90s, but if you look hard enough, you can still find some fantastic locks. For this part, I'm ignoring the butt rock/hair band era because the hair was bigger than the rocking. Here are some legit examples.
"Black Dog" by Led Zeppelin (1973 performance)
The whole band is rocking some great hair in this kind of relaxed version of the song. While Robert's head of hair is always magnificent, I think the important thing to note is John Paul's grown out page boy. I should also note that costuming doesn't hinder the rocking, so rest easy when you check out Jimmy's get up.
"Bad Boys Running Wild" by Scorpions (1985 performance)
Dude. Scorpions were good at what they did, and they did it with some good locks on their head. This time, their locks are blowing in the wind (the winds of change?). Not even those striped pants can get in their way.
"Molly's Chamber" by Kings of Leon (2006 performance)
While Kings of Leon are now rocking significantly less hair, at one point they realized the potential that long hair could bring to their music. I don't think I have anything else to say except that I wish they'd kept the bangs.
Questions to ponder:
1. Will long hair ever come back unironically?
2. What rocker dons the most glorious head of hair?