To date, I've smoked what seems like thousands of racks of ribs. Of the different ways I check for tenderness, the one I use most often is what's called the bend test.
Combining the bend test with the tear test and you have a surefire way to know when ribs are considered "done."
Note: These methods will come with time and learning how a rib feels when it's tender. This method is NOT for "fall off the bone ribs" or what I and others would deem overcooked ribs.
The bend test for ribs is fairly straight forward.
Simply grab the rack from one end with a pair of tongs - or gloves if you use nitrile gloves with cotton liners - at about the 5th rib (essentially less than half way).
You then pick the ribs up and allow them to bend at this rib. If the ribs bend at a 45 degree angle or more, they are considered done.
To help understand this visually, I took a picture of ribs at two different measured internal temperatures. One at 174F internal (roughly when I wrapped) and one at 202F internal (when they finished).
Here's the ribs bend testing at 174F:
As you can see, the ribs are barely bending, if at all. However, the ribs have great color and the bark has set. At this point the ribs have taken on more than enough smoke.
These are great visual indicators that it's time to wrap the ribs and speed up the cook time.
Here's the ribs at roughly 202-204F throughout the entire rack:
As we can see, the rack bends at roughly a 45 degree angle when held at the 5th rib.
Combining this bend test with a tear test will tell you when the ribs are done.
The tear test is fairly straight forward. With the bone side up, simply tear a bone away from the meat, if the tear is clean - meaning no meat is attached to the bone when you tear it - it's considered done.
You can also use your temperature probe to poke the meat between the bones. It should feel like it's gliding through like hot butter.
Note: The temperatures listed above are a rough guide.
Internal temperature is not the best way to tell when ribs are considered tender. Temperature simply tells us when the meat is safe to eat. Technically pork is safe to eat at 145F. However, at 145F, ribs aren't even close to tender.
Ribs will typically be probe tender in the 195 - 205F range.
The reason this isn't possible is because ribs that are smoked until they're fall off the bone will quite literally tear under their own weight when bend tested.
For lots of people who do barbecue, "fall off the bone" ribs are considered overcooked. Rather, you should be able to hold the rib, take a bite, and the meat should pull cleanly off the bone.
Again though, I'm not you - if you prefer fall off the bone ribs, leave them wrapped longer and cook them well beyond 205F. Somewhere like 210F-213F is more appropriate.
You could also use the tear test - you should be able to pull a bone easily off the back of the rack if they're fall off the bone style.