On Friday, May 24, 2019 at 9:27:51 AM UTC-7, Tom Kunich wrote:
I don't know how many of you watched the Amgen Tour of California but I think it was a Frenchman that got way hell and gone off of the front on Stage 5 I think.

As he was descending a rather long and steep climb he looked like an absolute beginner. All of his lines were screwed up and he almost went off the road several times. On one occasion he ran off of the road and up onto the sloped dirt siding.

I could not understand how someone that could ride 7 minutes off the front of a 140 mile race was so amateurish descending. He wasn't tired because he kept his lead for a very long way after the descent finishing with a full 7 minute lead.

Two days ago during some rain I was looking at videos and ran across one of them by a pro that showed himself descending almost identically amateurishly. The same bad lines though the corners and the same very dangerous lines.

He blamed this entirely on his disk brakes. He said climbing they drag and make noises and descending they cannot be relied upon to slow you properly. The upshot is he said that NO PRO would choose disk brakes over rim brakes and that this was just another gadget to up the price of a bike.

When I was talking here about how too F-ing powerful the large disks were and how much better the V-brakes were on a cross bike I got a whole lot of static. Well it appears that the same problem is on road bikes with the smaller disks.

They also have an aero disadvantage and I can tell you that the new bikes are so aero that you have to be careful descending in a group because you keep closing up on those in front.

The original idea was to have an alternate way to brake so that you wouldn't wear out the braking surface of carbon wheels. But using the artificial cork brake pads allows you to use a set of carbon wheels as long as you can the super-light aluminum wheels with standard brake pads.

Although we are presently in a trade dispute with China I don't expect that to last long and carbon wheels from China only seem to have one problem - they do not have much spoke tension and so move around too much in side winds. And they are spectacularly cheap.

While the US made carbon wheels are slightly more aero it isn't by much and unless you're riding TT's it isn't worth paying six to eight times the price.

Another problem - rim brakes put all of the braking forces at the strongest portion of the bike. Disks put the forces at the weakest. This forces manufacturers to make much heavier forks and rear stays. And the axles have gone to much larger sizes that cannot be used with quick releases. Pro mechanics no long change out wheels on bikes but make entire bike changes and that costs a lot more time than it used to.

All in all I think that disks are nothing more than something different to buy if you're a non-mechanical enthusiast that is likely to go with the flow.

Here is what some pros say: https://www.youtube.com/watch?v=OX_EPa0ZuSM

Discs do give better braking with CF rims, they don't heat rim glue, so you don't get sew-ups squirming around on the rims. If I were doing a long descent with lots of braking on sew-ups, I might prefer a disc. Otherwise, on a rapid descent on a racing bike with clinchers on aluminum rims on dry pavement, there is no a whole lot of difference between the two, assuming both are properly adjusted and the pistons lubricated. I own both and don't find much difference, except in ways that are equally bad, e.g. rim brakes grabbing at seams or with contaminants on the rim and discs shuddering or grabbing or screaming.

If disc brakes are juiced up to the point where light braking locks up the wheel, then that's a problem. If one is used to the requisite heavy hand to get good rear braking with a cable caliper brake, then that can be a problem with discs. I had to adjust after a couple of fish-tailing experiences..

Discs are the clear winner in wet-weather riding, but on dry pavement, it's just a matter of feel and personal preference. In professional racing, there are other considerations.

-- Jay Beattie.