I also liked the TKC80's and did the same. IMHO in the 21" size they are crap on big heavy bikes.
Flimsy weak thing that needed 35psi minimum pressure. It's square flat profile had me looking for something with more edge grip for both tar or dirt.
Currently using MT-21's. They walk around a bit more than the TKC-80's but i can push them harder around tarmac corners and simply a better off-road tyre. It's also one of the cheaper options here in Oz.
Please do tell about the how the bike feels with the clamp.
BMW R1200GS, Husqvarna TR650 and Mrs Q is on a F700GS