So what’s the big deal about Disc Road Bikes, compared to normal road bikes?
My reason for getting a disc road bike was to be able to honestly give an answer to the question “What’s a disc road bike like to ride, and are they any better?”. I’ve been riding my Cervelo S3 Disc for the last week, and in summary, it’s amazing. Specifically, the brakes are a lot stronger, allowing you to stop really quickly and smoothly – they aren’t “grabby” like they are on the disc brakes of mountain bikes. The great feature of disc brakes is the ability to use them on very long descents without the worry of overheating your rims.
The other feature with most disc brake bikes now, is the thru-axles in the wheels: this allows the rear of the frame to be made out of one continuous piece of carbon, instead of a brake-stay / chain-stay / tip for normal road frames.
The benefit of all this is a much stiffer bike, without losing compliance – you get the best of both worlds. This is why sprinters in the Tour like Marcel Kittell and Peter Sagan have been riding them recently.