I've so far hesitated joining this thread. First, let me be perfectly 
clear: I speak only for myself. Nothing I say should be construed as 
representing "Rivendell Policy" or "Rivendell Opinion". I prefer rim brakes 
99 to 1 over "disc" brakes. I put "disc" in quotation marks because, of 
course, rim brakes are disc brakes, with a much larger radius. And that 
makes all the difference. A front disc-brake wheel is heavily dished 
(uneven spoke tension, left to right). The proximity of the braking surface 
to the hub increases the stress on the pulling spokes, relieving the 
"pushing" spokes -- the flex on the looser-side spokes can work-harden the 
bend in the spoke elbow at the hub, and it will eventually break. Same 
thing with the rear wheel (only here the lower-tension spokes are on the 
non-drive, left side). These spokes are already prone to breaking over the 
long haul, as they flex more, and will work-harden more quickly. This 
increased stress would still be problemmatic on a non-dished disc-brake 
front wheel, as well, because of the increased stress all around, at the 
hub. Admittedly, replacing a broken spoke is easier, and less costly, than 
replacing a worn rim. Nonetheless, a dished front wheel presents additional 
problems -- as the primary braking instrument, the front wheel, when 
unevenly tensioned (side to side), can, under severe stopping conditions, 
become unstable, provoke an accident, or even "figure-8". Not good.

Additionally, disc brakes present a safety hazard to other riders. That 
spinning, thin disc can easily become a buzz saw when presented with a 
fallen rider's limb. Hence the ban on disc brakes by the UCI. This should 
be an alarm bell, at least.

Full disclosure: I use a disc brake as a "drag brake" on my tandem, so far 
with no problems. That's why is "99 to 1" as opposed to 100 to zero!

On Friday, May 13, 2016 at 7:19:47 AM UTC-7, Will wrote:
>
> Might be nice to push back to GP and encourage more of these posts. 
>

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