Prep. Cut three limes in half. Cut half of the fourth lime into 1/4-inch (6.4 mm) slices. Cut the remaining half lime in to two wedge.
Fire up. Prepare a grill for medium-high heat cooking, approximately 400°F (204.4°C).
Cook. Place the halved limes on the grill cut side down and allow them to grill until lightly charred and softened, approximately 4-5 minutes. Remove limes from the grill and allow them to cool.
Blend. Juice enough of the grilled limes to create 1/4 cup (59.1 ml) juice for a each pair of cocktails. Combine the lime juice, triple sec, tequila, sugar, and ice in a blender and blend until slushy.
For salted rims, rub lime wedges along the edges of 2 margarita glasses. Pour salt onto a plate and dip glasses in the salt to coat the edges.
Serve. Pour margaritas into the glasses, garnish with limes, and serve immediately.