I'm 15 stone and running dual disc on a stock bike and have never had any problems. I have been for a year now. I've run 180mm and now running 200mm, both have been more than powerful but 200mm.... oh my god! I side hop to my left and have never had problems... Your frame and tire will always get in the way first before hitting a rotor. I use Hope mono trials and have found them more than satisfactory and when i have used avids... i have found them to be more 'on, off' feeling. A well set up brake does make all the difference but have never had problems before. (same as with maggies) In wet weather my brakes have performed excellently and have reduced braking power ever so slightly. All i can say is give it a go or try a friends bike but don't dis it till you try it. Just ask anyone if they've seen me ride...... my brakes work well............ Rob, Thinkbikes.com