Why does Tracy have such big hair in Hairspray?

Tracy has such a big hairdo because it is the new style, and as she quoted in the beginning of the movie, "Hair can't just hang there like a dead thing on your cheek." Since the story is set in May/the beginning of June, 1962 in Baltimore, Maryland, the styles of young Americans is still like the sixties styles. The idea of her hair is symbolizing the aspect of big hair in the early sixties.