Preheat oven to 375 degrees. Place beets on a large piece of parchment-lined aluminum foil. Drizzle with oil. Season with salt and pepper. Wrap beets, enclosing them tightly. Place on a baking sheet, and roast until fork-tender, about 1 hour. Remove from oven; set aside to cool.
Peel beets when cool enough to handle. Using the largest holes of a box grater, coarsely grate beets into a large bowl. Drizzle with vinegar, and sprinkle with sugar. Toss to combine. Fold in sour cream, and serve.