Originally Posted by
FastJake
Except that the hubs, frame, and fork all have to be heavier than with rim brakes. We already know how much heavier because we can compare a current rim brake bike to a disc brake bike. I'd like to see these lighter rims though. That's a claim I've heard several times, and yet I've never seen any lighter disc-specific rims.
The frame, fork, and hubs only need to be marginally stronger. Fork probably the most.
The tech is still relatively young. Also as I believe UCI has not yet allowed discs in road races there is not yet incentive to create rims for race applications. If the approval sometime comes we will most likely see much more variety in lighter better performing carbon rims.
The heavier too stiff frames are also a product of too little experience with discs. At the moment there seems to be a bit of a panic with disc reinforcement which causes manufactures to beef up the frames too much. Furthermore most "road" bikes with discs currently are actually CX bikes which further creates an impression of overly stiff bikes due to discs.
I can easily envision a disc specific bike which is more aerodynamic than a caliper road bike, has the exact same ride quality and has a compareable weight in the 6.8kg area (which is the UCI limit)
One reason why discs might actually become prevalent in road bikes is the outbreak of discs in hybrids. It's not just MTB's anymore.