In a dutch oven over medium heat, saute garlic in oil for 1 minute. Add the roast; brown all sides. Combine vinegar, tomato juice, ketchup, sugar, salt and pepper, pour over roast. Cover and simmer for 2 hours. Add carrots and onions; cover and cook for 1 hour or until meat and vegetables are tender. Remove to a serving platter and keep warm.
Skim fat from pan juices. Add water to juices to measure 3 cups. Mix flour and cold water until smooth; stir into pan juices. Bring to a boil; cook and stir for 2 minutes. Season with salt and pepper. Slice roast; serve with vegetables and gravy.