Bring a large pot of lightly salted water to a boil. Cook elbow macaroni in boiling water, stirring occasionally, until tender yet firm to the bite, about 8 minutes. Drain and rinse under cold water.
Mix together mayonnaise, sugar, vinegar, mustard, salt, and black pepper in a large bowl. Stir in macaroni, onion, bell peppers, celery, carrot, and pimento peppers until well combined. Cover and refrigerate for at least 4 hours or overnight before serving.