Prepare your grill for hot direct heat on one side, and indirect heat on the other using split diverter plate. Sear the roast on all sides, 3-4 minutes per side over direct heat.  Carefully watch the roast during this process as one side of the roast is typically quite fatty and as the fat heats up it can drip down and cause flare-ups. Keep moving the tri-tip away from the flame if flare-ups occur.

Once the tri-tip is seared on all sides, move it away from direct heat and place it fat-side up on the grill rack over the diverter plate. Try to maintain a grill temperature of 250°F to 300°F.

Cover the grill and cook until the temperature of the interior of the tri-tip reaches 120°F for a rare roast, 130°F for medium-rare and 140°F for medium. At this point the meat will take anywhere from 20 to 40 minutes to cook, depending on how hot your grill is, how well done you want it, and the size of the cut. Note that the interior temperature will continue to rise at least 5°F after you take the roast off the heat.

Once the roast reaches temperature, remove it from the grill and let it rest, loosely tented with foil, for at least 10 minutes. Slice against the grain and serve.

If you are using a gas grill with a top rack, I recommend placing the roast on that rack, with an aluminum tray on the bottom rack underneath to catch the fat drippings. If you are grilling on charcoal or wood, you may want to turn the roast over every few minutes, for more even heating.