Add the sugar, water and 1/4 cup of the lime juice to a small saucepan. Bring to a boil, stirring until the sugar dissolves. Remove from heat and let cool.
Add a few ice cubes to two chilled highball glasses. To each glass, add 2 ounces of the lime simple syrup and 1 tablespoon of the remaining lime juice. Divide the grenadine between the glasses and top off with club soda.
Garnish with a lime wheel and 1 or 2 maraschino cherries.