I think the specificity of that Tulsa, Oklahoma setting is absolutely vital, and it gets overlooked sometimes because the greaser vs. soc thing feels universal. Hinton nailed a very particular kind of 1960s urban sprawl that wasn't a big city but wasn't rural either. The drive-in theater, the vacant lot, the park with the fountain—these are all liminal spaces on the edges of development, perfect for kids who themselves are on the margins.
The East Side/West Side divide is the entire engine of the plot. It's not just rich and poor; it's a geographic reality that dictates where you hang out, who you see, and what risks you take. Ponyboy walking home alone from the movies on the wrong side of town isn't just a bad idea, it's a violation of an unspoken territorial rule. The location makes the conflict inevitable and concrete. You can feel the tension ratchet up just by crossing a street.
That setting also creates the book's melancholy atmosphere. The sunsets Ponyboy talks about watching from the lot, the cold wind off the plains—it's a kind of beautiful, lonely backdrop that mirrors how he feels. Even the rumble happens in a secluded spot, away from adult eyes, because the city's layout provides those forgotten corners where this other society operates.