Season the tri-tip liberally with salt. Use 1.5 percent of the weight of the meat to determine your salt amount if unsure, so 16 ounces of meat would require ¼ ounce (or 7 grams) of salt. I prefer to let them sit in the refrigerator uncovered at least overnight. The ones I tested were in for two full days. Even if you plan to season the meat just before it goes on the grill, apply the salt first, then the other seasonings in a second layer to ensure the salt is even.
For the rub, mix the garlic powder and black pepper together. In another bowl, whisk together the vinegar and yellow mustard. Heat the oil in a sauté pan. Don’t get it screaming hot, just a nice shimmer on the surface. If the oil is smoking, it’s too hot. Add the spices and stir them in off the heat for just 20 to 30 seconds, being careful not to let them burn. Pour the mustard mix into the pan, but save the bowl. Be careful not to burn yourself. The hot oil may pop, but this step will halt the spices from cooking further. Pour the whole mix back into the mustard bowl, and whisk it together. Slather the entire surface of the tri-tip with the seasoning mixture.
Once you’re ready to cook, set up your grill for two-zone cooking. Put all the lit charcoal on one half of the grill and the tri-tip on the opposite side. Add some wood chips (I prefer mesquite for a short cook like this one) directly into the charcoal for a good dose of early smoke. Put the lid on the grill with the vent open. Come back in 20 minutes to check the internal temperature, and continue checking every 5 to 10 minutes until the internal temperature reaches 115 degrees (see above for tips on getting a good reading for internal temp).
Once the proper internal temperature has been reached, move the tri-tip to the hot side of the grill and sear it on all sides. Move to a cutting board and let rest for at least a half hour. With the fat cap still on, you may have to turn it over to find the grain for slicing. Slice the tri-tip thin, against the grain, and serve. The slices from the thin end will be well done, but as you move back into the thick portion it should be medium rare. Serve with a chimichurri or a salsa criolla on the side.