Combine vinegar, water, sugar, and salt in a saucepan over medium heat. Bring to a boil and cook until sugar and salt are dissolved, 3 to 5 minutes. Taste and adjust seasoning so the pickling liquid is pleasantly sweet, sour, and lightly salty.
Combine cucumbers, shallots, and chile peppers in a large bowl. Cover with pickling liquid. Refrigerate for a few hours to let flavors combine.