> I think this may be because the disc brakes for bikes are made as light as
> possible to compete in the market with standard brakes. They are okay for
> hard braking but might not be for sustained hard braking. I also don't
> know what kind of compound they use as a surface on the brake pads. So it
> might be something to do with this causing brake fade once they heat up.

I have disc brakes on my other mtn bike. They actually do handle heavy braking far better than any other brake I've tried, including drum brakes, with one caveat: You can't go dragging them all the way down long grades to slow your speed. Drum brakes have far more metal on the brake pads to dissipate heat than the tiny brake shoes on disc brakes. The correct way to brake with any vehicle to minimize heat buildup is to pump the brakes...let the speed build up some, then brake rather quickly and reduce your speed back to your cruising speed. If you repeat this over and over, (most) discs won't overheat. Because disc brakes stop far more quickly than drums, this works very well. Now if you've just gotta drag them brakes, better get some drums...