Stir salt, black pepper, garlic powder, paprika, onion powder, rosemary, and cayenne pepper together in a bowl.

Place tri-tip in a glass baking dish and coat on all sides with spice mixture. Cover the dish with plastic wrap and refrigerate for 4 hours.

Combine vinegar, vegetable oil, crushed garlic, and Dijon mustard in a sealable container. Cover the container and shake until ingredients are blended.

Remove tri-tip from the refrigerator. Let sit uncovered at room temperature for 30 minutes.

Preheat an outdoor grill for high heat; lightly oil the grates.

Place tri-tip on the preheated grill and brush with vinegar mixture. Cook for 4 minutes, flip, and baste. Repeat this process every 4 minutes until tri-tip is reddish-pink and juicy in the center, 25 to 30 minutes total. An instant-read thermometer inserted into the center should read 130°F (54°C).