AT81 is new Dunlop, stiffer side walls with a soft crown. RC is Reinforced Carcas desert version. I guess I should try one eventually. I run the MT16s @ 7 PSI, and yes I know all about the soft sidewalls. From running many of these Tubliss for three years now, I can tell you it does not matter in most cases. I've been racing a whole HS series for three seasons now plus trail riding in extreme rocks and never a failure. Yes the sidewalls break down but by that time the tread is trashed anyway from all the rocks. For the terrain here they work well for me, easy to mount and always seal perfect, and are relatively cheap. If its more rock than dirt I switch to an MT43 @ 6PSI. No way am I going to spend $130 on a tire to destroy in a few rides.