Many of those who read bicycle blogs will probably remember an article by Bike Rumor where one of their road disc testers lost all braking power in a descent, resulting in a trip to the hospital. The reason this happened was because the fluid in the brake lines boiled. And the reason brake fluid boils is because unlike on a car or mountain bike where there is plenty of metal to dissipate the heat build up from the pads squeezing the rotor, road bikes are typically made of insulating carbon fibers so the heat has nowhere to go but back into the lines.
The only solution in this case would seem to be cable-powered disc brakes, which are heavier, weaker, and less precise then their hydraulic cousins -but wait! There's another solution. The engineers at SRAM have been working with a fluid with a boiling point of 600 degrees, DOT6.
The DOT6 enhanced brakes will have the exact mechanism of the Avid mountain brakes, scaled down. The one drawback is that DOT6 fluid is extremely susceptible to contamination, specifically from water. Ed told me for every fifteen minutes the fluid is left in the open air its boiling point goes down 100 degrees- it'll just suck the water right from the air. This fact underlines the importance having good mechanics with adequate tools working on your bike.
So with boiling brake lines mitigated, the only issues left unaddressed are the compromised wheel stiffness because of the narrower hub flanges; the inability to swap wheels on the fly because of differences in rotor spacing and caliper position; and the weight penalty of carrying two spinning steel discs, thick aluminum rotors, a few ounces of fluid, a reservoir, fluid lines, and modified brake levers.
Are hydraulic disc brakes better than mechanical disc brakes? They are more expensive and difficult to service. Are these disadvantages worth it for the performance or are today's mechanical brakes the way to go?
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