Ok, I'm late to this thread. We tried custom 203mm titanium rotors on our tandem, with Avid mechanicals. 220km of riding, and the pads were gone, and the front rotor was showing wear. Great heat dissipation, but poor wear. We swithched to Shimano XT 203mm rotors, and all is well now. Heat is not a problem, as we use the brakes sparingly, even at speeds up to 60km/h. If the plastic melts, it's because you're riding the brakes. So far as I know, Avid is the only manufacturer that rates their mechanicals for tandem use. That's my $.02.