Add the potatoes to a large pot. Cover with water and bring to a boil. Reduce heat to a slow simmer and cook until tender, 15-20 minutes. Drain and cool.
In a large bowl, combine the cooled potatoes, the smashed eggs, pepper and salt.
In another bowl, combine the mustard, sugar, mayo, relish and pimentos.
Pour the mustard mixture over the potatoes and stir gently to coat.