Prepare an outdoor grill for cooking over medium-high heat. Combine the brown sugar, espresso powder, ancho powder, paprika, 2 teaspoons salt and 1/2 teaspoon black pepper in a small bowl.
Pat the spice rub on both sides of each steak (but not on the outside fat cap). Let the steaks sit at room temperature for 20 minutes.
Grill until the steaks are nicely browned with deep grill marks, 5 to 6 minutes per side for medium rare. Transfer the steaks to a serving platter to rest for 5 minutes before slicing.