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Old May 25th 19, 07:16 PM posted to rec.bicycles.tech
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Default Disk Brakes Again

On Saturday, May 25, 2019 at 3:11:02 PM UTC+2, Roger Merriman wrote:
wrote:
On Friday, May 24, 2019 at 7:07:31 PM UTC+2, jbeattie wrote:
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.


I was caught in heavy rain last week with my aero bike with CF rims and
rimbrakes. Braking power was almost non existing compared to Alu rims and
rim brakes. Every corner was a hazard and this was on flat terrain. CF
rims and disk brakes are a winner by far in wet conditions. Since CF
aero rims are the norm in the Pro peleton disk brakes are going to stay.
You better get used to it. In the mountain stage in the Giro yesterday a
lot of riders used diskbrakes. Weather conditions were dry btw.


What the pros want is in side show really, after all they use tubs etc, and
have support vehicles etc.

Disks have been pushed by manufacturers to the pro peloton, to catch up
with the growth of disks coming, from CX/gravel, bikes has been for few
years now.

Roger Merriman


Huh?

Aerodynamics makes sense, so CF rims make sense, so disk brakes makes sense. Simple. The only reason pro riders are/were reluctant to use disk braces is weight.

Lou
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