Trim fat on tri tip to 1/4" and remove membrane, if necessary.
Mix the seasonings in a bowl. Season the tri tip with the dry rub, reserving 1 tablespoon for later. Wrap with plastic wrap and refrigerate for at least 2 hours, or overnight if possible.
Preheat the smoker to 225°F, set the tri tip directly on the grill and close the lid.
Mix the remaining dry rub with 2 tablespoons of olive oil.
Smoke the tri tip for about 1 hour 30 minutes to 2 hours, basting twice during cooking with the olive oil/rub mixture.
The roast is done when the internal temperature reaches 125°F for medium rare or 135°F for medium.
Take the meat off the grill and let it rest for 15 minutes wrapped with tin foil. This allows the meat to come up to the proper temperature.
To serve, slice the roast against the grain in thin slices.