Barbecue a tri-tip by trimming off excess fat, rubbing spices onto the meat and roasting it over indirect heat for 20 to 60 minutes. Do not trim off all the fat, as it provides a base for the meat while cooking.
Begin by making a dry rub for the tri-tip. A common tri-tip rub recipe includes 1/3 cup of salt, 1/3 cup of black pepper and 1/3 cup of garlic salt. A good complex dry rub mixture is composed of 2 tablespoons of finely ground coffee, 1 1/2 tablespoons of kosher salt, 1 1/2 tablespoons of granulated garlic, 1 teaspoon of black pepper and 1 tablespoon of brown sugar. Also add 1/4 teaspoon of cayenne pepper, 1/4 teaspoon of ground cloves and 1/4 teaspoon of cinnamon for a good complex dry rub.
Refrigerate the tri-tip for one hour, and remove the meat an hour before barbecuing it. Pile coals onto one side of the grill, and sear the tri-tip over the coals for five to 10 minutes on either side. Remove the meat from the coals, and place the tri-tip on the grill over the space where coals aren't present. Cover the grill, and roast the meat for one hour. Use a meat thermometer, and remove the tri-tip from the grill once it has reached an internal temperature of 145 degrees Fahrenheit. Loosely wrap the tri-tip in aluminum foil, and let it rest on a cutting board for 10 minutes.