In a small bowl whisk the rub ingredients and season the pork ribs evenly with the rub.
Prepare the grill for direct and indirect cooking over medium-low heat (300° to 350°F).
In a medium saucepan combine the onion, beer, orange juice, lime juice, and garlic and bring to a boil over high heat. Pour this braising liquid into a large grill-proof Dutch oven and place over indirect medium heat.
Grill the pork over direct medium heat, with the lid closed, until brown on all sides, 8 to 10 minutes, turning four times. Transfer the pork to the Dutch oven. Place the lid on the Dutch oven or cover tightly with aluminum foil. Cook over indirect medium heat, with the grill lid closed, keeping the temperature of the grill as close to 300°F as possible, until the meat is fork tender, 2¾ to 3 hours, turning the pork once every hour.
Using a slotted spoon, transfer the pork and onion from the braising liquid to a sheet pan and set aside to cool slightly. Keep the Dutch oven on the grill.
Increase the temperature of the grill heat to high heat (450° to 550°F).
While the grill is coming up to temperature, move the Dutch oven over direct high heat. Bring the braising liquid to a boil over direct high heat, with the Dutch oven uncovered and the grill lid closed, and cook until the liquid is reduced by about half, 5 to 7 minutes. Meanwhile, shred the pork and discard any large pieces of fat.
When the braising liquid is reduced, move the Dutch oven over indirect high heat. Pour off all but a few tablespoons of the braising liquid into a small bowl. You want to have just enough liquid remaining to coat the bottom of the Dutch oven. Add the shredded pork to the Dutch oven and cook, with the grill lid closed, until the edges are slightly crisp and caramelized, 10 to 15 minutes, stirring occasionally. As the pork crisps, drizzle it with the reduced braising liquid, 1 tablespoon at a time, to prevent it from drying out. You may not need all of the braising liquid.
Serve the shredded pork and onion warm in tortillas with salsa and lime wedges.