Which juice is balanced with vodka in a Greyhound cocktail?

A Greyhound cocktail is traditionally made using vodka and grapefruit juice, creating a refreshing and balanced drink. The tartness of the grapefruit juice complements the smoothness of the vodka, resulting in a harmonious blend of flavors. This cocktail is particularly known for its simplicity and the way the citrus notes from the grapefruit enhance the spirit's profile.

Other juices mentioned, such as orange juice and pineapple juice, are typically associated with different cocktails that emphasize sweeter and fruitier profiles rather than the tartness that defines a Greyhound. Lemon juice, while also citrusy, is generally much sharper and acidic compared to grapefruit juice, which could overpower the cocktail rather than balance it. Thus, grapefruit juice is the ideal choice to achieve the intended taste of a Greyhound cocktail.