Originally Posted by mtseymour

In dry weather, rim brakes or disc brakes will not fail if used with proper technique and in good working order. I've used cantis, sidepull, and V-brakes on fairly demanding descents without any failures. It's just a good idea to check for rim/pad wear and excessive heat.

However, I have no doubt that hydraulic brakes work better in the most taxing conditions. Everything else being equal, a tandem with hydraulic disc brakes should descend the same route much faster with more reliability. With disc brakes, it's easy to make multiple steep descents (several miles at 6% or steeper) without worrying about brake fade or worn pads. The same team will be slower and more cautious when descending with rim brakes. No one has bothered to test this objectively because there is so much downhill or enduro mtn bike results to show that disc brakes offer more power, better modulation, and better reliability (rain or shine). It's no surprise that disc brakes are also the preferred choice for motorcycles and cars.