Indirect Gas grilling with smoke is a technique for grilling larger, thicker foods that might burn if grilled directly. When using this technique, place food next to, instead of directly over the fire. If using a gas grill with 3 or more burners, turn on one of the side burners and leave the others off. Adjust the burner until the thermometer reads 400 degrees. If using a two-burner grill, turn on one side and leave the other side off. You will need to place a smoking box or a foil pouch if wood chips with holes poked in it over the burner that is ignited.
Place tri-tip roasts on the grate over the burners that are off. The larger side should be toward the heat source.
For a medium rare tri-tip, indirect grill for 30 -35 minutes flipping roasts half way thru cooking time. Verify desired cooking temperature with a kitchen thermometer.
When tri-tip is 10 degrees from desired doneness temperature move roasts over direct heat. Sear all sides of the roast.
Remove from heat and let stand 10 minutes before slicing.