Tri-tip is a great cut of beef. It's not too expensive, and loaded with flavor. I've fixed it a number of ways, including grilling using the direct heat method (right over the coals). I've roasted it, braised it, cooked it in a pressure cooker. Yesterday I grilled using the indirect method and it worked great!
Basic method is simple. I coated it in a rub and let it sit for several hours in the fridge. Then indirectly cooked it for about an hour with some hickory wood. After the hour I hit it with a few things to help keep it moist and wrapped it tightly in aluminum foil and kept it in the grill for 2 hour hours. It was terrific.
First up the rub, equal parts kosher salt, white pepper, onion powder, paprika, and brown sugar. I used about 2 Tbs each. Then rubbed a 2-3 lb tri-tip on all sides and wrapped tight in plastic wrap and relegated it to the fridge.
About 4 hours before dinner, I put the meat on the counter to warm up nearer to room temp, then I set up the grill. I use a large kettle grill, charcoal. I started about a chimney full, about 2.5 scoops with my cut-down gallon milk jug. I let them get well started and then split the in half to each side of the grill. I added an aluminum pan inbetween the two piles, added a couple of pieces of hickory chunks that had been soaking in water for about an hour. I make sure I have two smaller pieces well soaked, smaller because they slip into openings in my grill grate easily. Then I put on the grate, let it get hot and brush it and coat with some vegetable oil. Then I position a thermometer probe to read the temp right in the middle of the grill, just below where the food will be placed. I half close the lower air vents and almost completely close the upper. I am after 225-240F, no hotter or you will dry out the meat.
I put on the cover and let it get nice and smokey while watching the temp. At the point the meat is still on the counter. Once I am sure the grill isn't getting too hot, I put it on the meat, fat side up, right over the aluminum pan and close it quickly. For the first half hour, I watch the temp very carefully, keeping it no higher than 240 using the upper air vents for control. It's not a fine-tuned as a good smoker, but I don't smoke meats that often to need one. As long as you are careful, a kettle grill works fine.
After a half hour I take the the cover off and check out the coals and the wood. I usually have to add the reserve pieces of wood and maybe a couple of briquettes. I also brush the surface of the meat with a little apple juice. I like the slight carmelization you get from the sugar in the juice. It also helps I try not to add too much charcoal because the fire can get too hot to quickly. If that happens, I close the bottom air vents further and keep trying to regulate using the upper vents.
A couple of interesting things. I never turn the meat. We are cooking using the indirect method, not searing, so turning the meat isn't needed. Plus if you put the fat layer on the bottom, it will just melt off and not tenderize and flavor the meat.
OK, after the first hour the meat has absorbed all the smoke you need. So get a large piece of aluminum foil. I like the heavy duty, wider than normal sheets. Overlapping smaller sheets tends to leak. OK, I lay it out between a couple of hot pads, this way I can create depression for the meat. I pull it off the grill and hit it with a couple of pats of unsalted butter, about a quarter cup of brown sugar, and a quarter cup of apple juice. Seal it up very tight and put it back on the grill. The additional ingredients are what help keep it very moist. In all honesty the first time I did this recipe, I did overcook it a bit, but it was still nice and juicy.
Every half hour I check the coals and keep it going, adding just a few briquettes at a time. Again, you are looking for low and slow!
After 2 more hours, it would be ready. Smoked tri-tip as tender and juicy as a good brisket. Let it rest about 15 minutes and slice it across the grain into 1/4 inch slices. While it's resting, you can take the liquid from the foil packet and reduce it on the stove by about half and it makes a great sauce. If you don't feel like doing that. get a large bowl, pour in some of the liquid from the foil packet and as you slice the meat, put it in the bowl.