Originally Posted by
Wheever
You know, I hear this all the time, as though nothing unexpected ever happens to ordinary riders; as though cars and other riders and dogs and road conditions are always predictable. Those of us who ride in traffic, especially in urban and suburban areas, can't always "plan" when we're going to have emergency brake to save our lives. It's actually not about being a pro or racer.
Thing is, disc brakes require less time and effort and hand strength to reach full effective braking force in all conditions due to the fact that the pads sit .5mm or less away from the rotors, whereas rim brake pads sit farther--usually much, much farther--away from the rims, and can take milliseconds longer to begin to "grab". (Hydraulics also respond much quicker than cables.) This may not seem like a lot, but at speed, in an emergency, those milliseconds could be the difference between a close call and death or injury. Additionally, disc brakes are much easier to modulate than rim brakes--at least hydraulics are--allowing incredible precision in applying just the right amount of braking force.
Happens, naturally, that I have a story regarding this very thing: the quicker reaction time of discs in saving my life. Bombing down a steep hill, doing something under 30mph, some ******* decided to U-turn, with no signal, right in front of me. Say less than 50'. With disc brakes, I was able to feather and hold the brakes right at the point before they locked. My tires were *literally* squealing on the pavement. I stopped so close that I had to turn my front wheel to the right so as not to hit it against the side of his car. I was close enough to reach out and pound on his roof with my fist as I yelled curses at him. ONE FOOT--That little initial millisecond it takes the rim brakes on my other bike to activate and grab--would have resulted in me hitting his car and flying over, and being very badly injured. This one experience convinced me of the complete superiority of disc brakes--between the stopping power and the fast response and ability to finely modulate the deceleration. I, personally, will never ride anything else again.
It doesn't seem like a lot because it isn't a lot ... completely overwhelmed by other things that influence stopping distance.
I just got off the phone with a buddy of mine who crashed on his tandem this weekend. And knowing the road he was descending (very, very steep and winding), it could have been much, much worse. How did he crash? His brake failed ... a disc brake.
He's a pretty competent mechanic, but had someone else working on his brakes for him, because like any disc brake, they're not as simple as rim brakes to adjust and figure out. So one could argue that at the heart of the matter, his crash would not have happened but for the disc brakes.
I'm not raising this because I think that disc brakes are any more of less prone to failure than rim brakes. I also know someone who had his carbon rim delaminate going down another nasty descent ... and that wouldn't have happened with a disc brake (the rim brake contributed to the rapid failure of the wheel). And tire failures are a possibility with rim brakes if the pads are not adjusted properly. Seen that too.
But anecdotes are just anecdotes. And there are a lot of factors that go into how well you can stop at any given time, and the risk of failure.
I would use discs on a tandem or on an MTB, because IMHO, their advantages outweigh the disadvantages in those applications. Not so much a road bike. If they can figure out a way to modulate fore/aft braking power (easier with a hydraulic disc system, I would think), I might be convinced otherwise.