i am also led to believe that the way the pads work in disc brakes is mainly one direction of rotation so if u are up on your back wheel it puts force in other both directions depending on correction but i'm just a noob i read that some were els so correct me if i'm wrong sorry i got it rong its from this where i jumped to the wrong anser "as for disc brakes, while some trials bike frames are built to accomodate disc brakes on the rear, the disc tabs on the Trek Bruiser aren't ideal for trials. y'see, while the bike is up on the rear wheel and the brake is locked the brake tabs are having forces exherted on them from the wheel being pushed backwards; if you have to do a corrective hop backwards and brake while the wheel is travelling backwards, the forces are even greater. 98% of disc tabs are designed to absorb brake forces from the bike travelling forwards, so they can rip off if trials moves are performed on them." quote bEavoLa (mbuk.com/forum"