Take a knife and trim the loose fat and meat from the roast. You do not want to remove the fat cap as it helps protect the meat from the flame's heat, but you want to remove any loose pieces.
Season the tri-tip liberally with the rub, then allow the roast to rest at room temperature while you make the chimichurri and fire up the grill.
Prepare a bed of charcoal with a charcoal chimney, then add a few chunks of your preferred wood on top. Once the wood catches fire, the grill is ready to go.
Lightly oil the grill grates, then place your tri-tip on them. Set the grill grates about 8” from the bed of coals and wood.
Allow the tri-tip to cook for about 30-40 minutes at this height, flipping every 5-7 minutes, until it reaches an internal temperature of 115°F.
Lower the grate so that the roast is a few inches from the coals and allow it to sear on all sides until it reaches an internal temperature of 130°F (for medium rare).
Remove the roast from the grates and allow to rest, tented in foil, for 15 minutes.
Slice the roast against the grain and serve immediately alongside homemade chimichurri.