Prepare glaze first. Bring ketchup, brown sugar, maple syrup, and water to a simmer over medium heat. Stir often and watch for burning. Reduce heat if necessary. Add cider vinegar and salt. Stir through. Add bourbon and let the mixture simmer for 3-4 more minutes over medium-low heat. Once all ingredients are well combined and sugar has melted through, remove glaze from heat and let cool.
Preheat grill for medium heat with indirect cooking.
Cut off any straggling pieces of fat or meat from the spare ribs. Using a paper towel, grasp membrane on the back of the ribs and pull away from the bone.
Blot the rack of ribs dry with paper towels. Combine seasoning rub and apply all over ribs, front and back.
Place ribs onto the grill and cook for 2 to 3 hours or until the internal temperature of the meat reaches at least 185 degrees F. Adjust heat and placement of ribs on the grill as needed.
Warm the glaze in the microwave or stove top. There is no need to bring it back to a simmer, but warm it enough so that it doesn't reduce the temperature of the ribs on the grill once applied.
Begin brushing glaze onto ribs during the second half of grilling or when they reach an internal temperature of about 135 degrees. Repeat process several times during the remaining cook time. This will provide you with a nice caramelized candied coating on the ribs.
Once they have reached the appropriate temperature, remove ribs from grill and tent with foil. Let meat rest for 10 minutes before slicing. Slice between bones and serve with your favorite sides.