Step 1Bring a large pot of water to a boil; generously season with salt. Cook pasta, stirring occasionally, until very past al dente, about 2 minutes more than package instructions. Drain.
Step 2Meanwhile, in a large bowl, whisk mayonnaise, vinegar, granulated sugar, pepper, and 1/2 teaspoon salt. Using a rubber spatula, fold in pasta, onion, carrots, and celery. Cover and refrigerate at least 2 hours or up to overnight.
Step 3Let stand at room temperature 20 minutes before serving.