I have used them on an 1150 GS and both of my 1200 GSs. On the GS, they are a fantastic tire. I like them for everything. In mud, you are fighting a big bike with big knobbies, so things aren't so great right from the beginning...
I find them to be great in sand, gravel, dirt, and they are excellent on pavement. The biggest issue for me is that I rarely get more than about 2500 miles out of a back tire and maybe 5000 out of the front. I will admit that I run them pretty hard on pavement though.
This is running a casual pace in Northern Arkansas on the 1150. It was easy to drag the pegs or the Jesse bags with the TKCs on the bike.
You CAN do mud, you just have to be careful!
I made it through on my 1150 with TKCs, this 1200 was not so lucky
But... if you play the game long enough...
You find out that one of those collapsible army shovels comes in REAL handy!!
There was a "wee" bit of mud on the climb up this mountain, but it was worth it!!
But sometimes, even on dry ground... things don't go as planned
The knobs are big, so you feel them when the tire is rolling slow. Once you get moving, it smooths out. There is a bit of noise at speed, but nothing like a regular knobby on a dirt bike. There is no howling.
I have a set on my 07 1200 GS right now.
I rode a LOT of these kinds of roads in North Carolina on the 05 1200 GS with the TKCs and we were running a pretty hot pace at full lean. No problems.
On my 05 1200 GS, I most recently used the Heidenau K60s for a trip to Utah and Colorado. If you are going to be doing more 50/50 with maybe more street, these are good tires. I found them to be a bit noisier than the TKCs and not as good in sand, but otherwise they did quite well over a wide range of surfaces. Like the TKCs, you will want to avoid any serious mud... The good thing is that they last considerably longer than the TKCs.
Here's a sample of the roads from Utah
US 550 with ice and sand on it, I did tip toe through this because the bike was wiggling around at lean
Those are K60's on an 09 1200 GS. It was dry packed dirt with ruts and rocks. No problems.
Same bike on loose crunchy gravel, a wee bit of sliding, but that was fun
My bike in a mix of sand and small gravel a few inches deep, no problems
Dry red sand, no problems, but if it had been wet...
Rocky ledges and big loose rocks in dirt, no problems
Smooth coarse dirt, total blast!
ONE HUGE ROCK... no problems...
Loose gravel on hard packed and steep surface with rain, no problems
Hard packed sand mixed with rocks, no problems
Miles of DEEP and LOOSE sand with LOTS of ruts... hang on and NEVER let off the gas!!! I was really wishing I had the TKCs here, and this is the smooth easy part where I was able to stop and catch my breath!