^^^ What is your rib smoking procedure out of curiosity? I can see the meat is slightly rebated on the bone implying it might have used a little longer in the cook. Also carving them all up front will accelerate drying as now they are all exposed to air internally. IF you're pressed for time, even transferring to the oven wrapped in foil to accelerate can help. Generally, tough/dry ribs are underdone. As they cook longer, they will break down and get less tough. Getting the sweet spot means they will be moist, succulent and have a slight chew or even begin to fall off the bone. Going too far, they will still be fall-off-the-bone style but also begin to dry out. That's the general spectrum of rib done-ness.
I do mine for 5-6 hours with a few variances in foiling vs not depending on the type, size and desired texture of the meat.
In general, the only moisture you develop inside the meat is what already there--fats, connective tissue, water, etc. Developing the most juicy result will solely depend on rendering what is already there to the fullest potential without going over and beginning to dry it out. This means staring with a cut that has sufficient internal marbling and then cooking low and sufficiently long to render those tissues but not long enough to begin overdrying. There are some slight exceptions like liquid injections but those are more so for flavor as those will perform some internal basting but largely get evaporated on long cooks and any leftover will certainly come gushing out once you cut into it.
And generally speaking, any external moisture source like water pans or spray bottles are for bark development as you cannot get external moisture to penetrate back into the depths of the meat. Same goes for the fat cap, some folks believe leaving a healthy fat cap on top will let it "baste back into" the meat but its not really the case.
So any meat that seems dry is really just either undercooked (not fully rendered internally) or overcooked (too rendered with moisture loss).
You might want to experiment a bit with the time and procedure to see what works best with the gear you have. ITs hard to dedicate the smoker to one thing for the entire time so i'll often use the oven in conjunction if a step doesn't require smoke. And there's always a limit to how much smoke a cut will benefit from--about 3 hours is all ribs will absorb if you have good smoke.
Although this is for beef, heres' an interesting timeline for how the tissues begin to break down during a cook. IF you've every heard of "The stall", that happens right around 150*f for big roasts like brisket and butts that get taken to 200+ as the evaporation phase sets in.
COOKING MEAT TEMPERATURES
105F/40C - 122F/50C --Calpains begin to denature and lose activity till around 105F, cathepsains at 122F. Since enzyme activity increases up to those temperatures, slow cooking can provide a significant aging effect during cooking. Meat should however be quickly seared or blanched first to kill surface microbes.
120°F/50°C -- Meat develops a white opacity as heat sensitive myosin denatures. Coagulation produces large enough clumps to scatter light. Red meat turns pink.
140°F/60°C -- Red myoglobin begins to denature into tan colored hemichrome. Meat turns from pink to brown-grey color.
140°F/60°C -- Meat suddenly releases lots of juice, shrinks noticeably, and becomes chewy as a result of collagen denaturing which squeezes out liquids.
160°F/70°C -- Connective tissue collagen begins to dissolve to gelatin. Melting of collagen starts to accelerate at 160F and continues rapidly up to 180F
NOTES: At 140°F changes are caused by the denaturing of collagen in the cells. Meat served at this temperature med-rare is changing from juicy to dry. At 160°F/ 70°C connective tissue collagen begins to dissolve to gelatin. This however is a very lengthy process. The fibers are still stiff and dry but meat seems more tender. Source: Harold McGee -- On Food and Cooking
Scattered among the muscle fibers are fat cells which store energy for the muscles. Fat is crucial to meat texture. Waxy when it is cold, fat does not evaporate when you are cooking as does water. It melts and lubricates the fibers as they are getting tougher under the heat. Fat is also the source of much of the flavor in meat. As the animal ages the flavor compounds build up and get stronger. After the animal is slaughtered, the fat can turn rancid if stored improperly or too long.
