The MK2 has the side knobs in a fairly normal position sticking diagonally outwards from the upper edge of the sidewall, so the widest point of the tyre is the edge knobs. The RQ/TK’s side knobs are further inwards so the widest point of the tyre is the sidewall – this makes the volume of the carcass and height of the tyre much larger for their width.
I’ve found the RQ/TK 2.2 works well in mud, its compound being particularly good on wet roots, tons of braking and driving grip in the slop but doesn’t do turning unless you crank it right over to engage the side knobs so in the mud it’s definitely a commitment tyre. In the dry it’s much more tolerant of poor cornering technique.
It’s my favourite year-round rear tyre by a wide margin, especially considering the excellent wear rate for such a sticky tyre and the rolling speed considering how grippy it is. As a front tyre its lack of tolerance of insufficient lean angle in the loose conditions doesn’t help when I’m having a crisis of confidence so although the hardtail is running them front and rear the big bike has a Magic Mary up front which has the biggest edge knobs ever!