I have a stock DR-650SE that I did the Colorado BDR on. I did it with partly worn Bridgestone Trailwings, the OEM tire that came with the DR.
I think a lot of reviews of tires don't consider that the different sizes have notably different profiles and fitment depending on the size and the wheel.
After reading numerous positive reviews of the TKC-80 I decided to fit to the DR. At the same time, I dropped from stock gearing down to a 14 tooth front sprocket. I knew that the grippier tire would require lower gearing to pull. A slipping tire is like a torque converter and often works quite well.
Obviously, the TKC-80 is a more aggressive tire and will be worse on the street. I know what that is like. I had Golden Boys on a KLX-250S and was fine with them. The profiles were sensible. I know how much worse the braking distances are. I found that going from the (made in 2006~, 2,000 mile) Bridgestones to the TKC make front stopping go from stoppies to a skidding front tire. Which is fine for normal use but something to consider.
The carcass stiffness is rather medium in my opinion for both the Bridgestones and the TKC-80, thus feedback and durability seems rather equivalent.
There was a great issue I found with the TKC-80 on the DR-650. The front profile is very flat, not allowing for much lean. I think that's fine and to be expected. The problem is that the rear profile is like a V, much like a track day tire. Thus the back end of the bike wants to fall into corners and you fight it with the front. Obviously, some geometery adjustment influences these behaviors, however the profiles are so staunchly different that it is inevitable and I think there is no great adjustment around it. This took my driveway riding from having extremely confident lean angles in sharp turns to notably less pronounced (faster) turns on the driveway. Obviously, I could turn to the steering stops with either tire, but I could confidently and controllably lean with it much better on the Bridgestones which were over ten years old.
The tire profile mismatch is always evident. Personally, I prefer profiles to be matched or have a shaper profile in the front than the rear. That way the front pulls the rear down and not vice versa. I am speaking partly relatively, but I think largely it is true. If you are confused about "tire profiles", you can search on Youtube for "Dave Moss tires" and learn quite a bit.
Now, the TKC-80 is "fine" on road. Buzzier, for sure, but livable. Not great. Off road they are notably grippier. I found at my sandy property the TKC-80s were perfect for going sideways in the sand. That profile behavior (or perhaps sometime else) seems to lend itself perfectly to pitching the tail out, leaning, and being in full control.
Now, say on rockier and hard surfaces, I don't think the TKC-80 had any real advantages. In fact, I'd say in some cases a street tire does better than a knobbie as softness is the main concern for gripping hard and jagged rock. Of course in the sand and mud the tread is lovely, but in quite a great variety of terrain the deeper knobs offer little extra advantage.
As I said earlier, with the TKC-80 I dropped a tooth on the front. Incredibly, I found the bike bogging down more in first gear even with a lower tooth. The TKC-80 grips so much in the rear that it really has to work a lot harder, even at street presure. With that grip, in the sand I had to be much more careful with the throttle and clutch to keep from stalling it.
To add insult to injury, riding with the 14T on the highway was simply painful. Some people say they don't mind it. I thought 70mph with that 14T sprocket was much too buzzy and made the bike feel maxed out. With a 15T sprocket it was livable and seemed to make the best of the torque of the motor.
People complain left and right that the stock gearing on the DR is not low enough and I'd say they are right, if they have aggressive tires. Interestingly, with the Bridgestone Trailwings I had no problems with the stock gearing. This was doing the Colorado BDR, going up passes of almost 13,000 feet, up rocky sections in a particularly rainy season. And certainly there is rougher terrain than the Colorado BDR but it was particularly wet and muddy this time around, I would say more challenging than normal. And yet the Trailwings and stock gearing managed it just fine. Were the Trailwings secure in the dirt? Absolutely not, but I managed fine as a novice dirt rider.
So now I have a DR-650 that's no longer even potentially highway comfortable and still isn't geared as low as I'd like. This is coming from a bike that did the BDR just fine with a balding rear Trailwing in muddy conditions. What's the point of the TKC-80 on the DR?
Now if I were doing Moody Hill or only riding in sand/mud, of course I'd want the TKC-80 or an even more aggressive tire. But then I wouldn't like it as much on the street and I'd want to gear it down even more.
Thus, the simple tire change turns the bike from a compromise dual sport into a pigly dirt bike with overly tall gearing, even with a 14 tooth in the front. Or you could leave it as is, with a 15 tooth in the front, Trailwings, and let the bike slide around a little more. I don't recall any section on the BDR that I had to use the clutch exessively on. The rear would just slide around a little more to compensate, acting a bit as its own slipping clutch. Quite brilliantly, I think.
Unless your riding is purely dirt I cannot recommend the TKC-80 on the DR-650. And if it is purely dirt, I recommend a different bike. My next tires will either be Trailwings or the Heidenaus. Sadly, they only come in 130/80 in the rear but I saw a DR-650 with 130/80 Heidenaus on the rear and the profile looked fine. Even though on paper it's too big of a tire, in practice it seemed just fine. Those have a chance at being a good compromise of a more dirt worthy tire without having mismatched profiles and requiring a gearing change. And of course I'll be going back to the stock gearing.
There are some actual "free lunch" changes you can make. Fork emulators will help make the traction requirements a lot less up hill in rocky sections as the bike won't buck off of the rocks as much. Setting the suspension sensibly can help you make the most of street-oriented tires and let you have more fun on the road and the dirt.
If you really wanted to use the DR-650 as a dual sport or adventure bike with the TKC-80s, I believe changing out for a notably lower first gear would be necessary. Then you'd have to deal with a large and awkward gap between first and second, but I think it could be livable.
So while I do recommend the Trail Wings instead for the DR-650 as a general rule, high speed jaunts on the Trail Wings in the mud are not recommended: https://www.youtube.com/watch?v=TUXNczK3VWg&t=414s
Update as of 2018-05-02:
I was able to dial in the handling quite a bit more with the TKC-80s on the bike. Basically, with the extremely square front tire, you have to run a lower than expected pressure. For me, that is right about 22PSI. Much less and it starts to feel a bit vague. Much more and the sidewall won't flex down enough to force it into giving the profile the bike wants at a given lean angle.
I also had to take the preload spacers out of the front forks and have the sag matched front and rear, at about 4". Keep in mind, I have fork emulators up front and there is a tiny bit of preload -- it's not just flopping around. Before, I was running maybe 2" of dynamic sag at the front and 4" with the rear. With the properly pointy Bridgestones, this was not a problem. If I were to set the bike up with 2" of dynamic sag front and rear, the ride would be notably stiffer (effectively, worse at low speed and better at high speed), and the bike would be taller than I'd like for technical work. Lower center of gravity makes a huge difference, standing or not.
With these changes, I can be reasonably aggressive on the street and I'm happy with the dry handling. I can make the rear slip out fairly often in the dry but it has to be fairly deliberate. In the wet, it's a whole other story. The wet grip is not good on these tires. It's still such a light bike that it's very manageable and approachable. Just very, very easy for me to slide around a wet intersection. I can live with this on the DR but I would not want that little grip on a heavier bike, especially a heavier and taller bike.
Now, I have noticed the noise and it is awful. The problem with knobby buzz is that it blocks out almost all of the other tire noise on the road. Whereas before I could hear cars and trucks next to me without looking at them, I can no longer and have to be much more vigalant about using my mirrors. I don't think the TKC-80s are alone in this -- any notably knobby tire is going to make a significant amount of noise which is significantly less safe. Being able to tell where an approaching vehicle is just from the sound is extremely helpful, without that you are almost deaf on the road. Highway speeds are quite loud and I find myself wanting ear plugs much more often than with street tires.
Likely with the reduced preload in the front, the forks will bottom out too easily. So I'd have to setup the bike taller to make it work on the street and in the dirt, and then technical work is much more of a challenge. So in that regard, the Trailwings are notably more flexible even offroad. Unless you'd want to setup the bike with 2" of preload in the front, 4" in the rear, not handle on the road, and then be fine in the dirt.
There is an advantage with the square front that I did not realize before. Shallower profiles are easier to balance on, less of a tipping surface. Not that the bike is hard to balance normally, but the front is useful for that. The TKC-80s might make an okay trials tire. While the rear is more of a V, I find most of the balance comes from the front and lower pressures and shallower profiles can help with that. Squarer profiles do seem to require lower pressures.