On Fri, 31 Jan 2020 09:45:58 +0100, Tosspot
wrote:

On 31/01/2020 01:55, John B. wrote:
On Thu, 30 Jan 2020 19:11:13 -0500, Frank Krygowski
wrote:

On 1/30/2020 5:18 PM, Tim McNamara wrote:
On Wed, 29 Jan 2020 17:30:02 -0800 (PST), Tom Kunich
wrote:
I've been looking only at the advertisements for direct mount brakes.
...

The pictures I have seen show the cable entering the brake exactly like
a sidepull brake, but the pivots are reminiscent of Mafac Racers with
brazed-on posts.

https://www.cyclingweekly.com/news/l...-future-193731

I have Mafacs with braze-on posts on my randonneuse and they work
excellently with very good modulation and power; the Racers are paired
with modern Campy Record brake levers and it is a good combination for
me. The centerpulls offer excellent clearance for fenders and
moderately fat tires (700 x 31). The design also allows the brake pads
to have some clearance from the rims in case the wheel gets slightly out
of true.

I first heard of centerpulls with brazed on posts about 40 years ago. I
considered them when modifying the frame of my old Raleigh, but went
with cantilever bosses instead. But I suspect the braze-on centerpulls
would have worked about as well.

I've not tried the direct mount brakes, but they do remove the straddle
wire from the equation. That ought to improve efficiency, if greater
flexibility wasn't created in the brake arms.

The straddle cable isn't a source of flexibility (if that's what you're
implying) if you shape it ahead of time to run in a straight line from
the saddle to each brake arm. Most of the lost motion occurs because
straddle cables are naturally straight, and when installed, are bent
into a curve to reach from brake arm to saddle to brake arm. If there's
no curve, there's negligible lost motion.

Somewhere, I've seen photos of rigid links used to replace the straddle
cable. I suppose that might be even better, but I don't know of a
supplier. They might not be hard to fabricate, if you're into that thing.

Another source of flexibility with center pulls or classic cantilever
brakes is the hanger that stops the brake housing. Especially on front
brakes, that's often a thin steel or aluminum stamping that flexes a
lot. A rigid hanger greatly improves the brake's feel, IME.

About the website linked above, I have some agreements and some
disagreements. I agree that the chainstays are a terrible place to mount
any brake. Like the guys quoted, I don't doubt that some of the other
purported benefits (aero, rigidity) exist, but I think the differences
are likely negligible. Especially, there are other ways to get rigidity.

But I strongly agree with the statement near the end: "However, we think
many brands that fit direct-mount brakes at the chainstay are doing it
for trend or marketing reasons."

Because, fashion! Fashion is weird and powerful.

I've installed center pull, cantilever, single pivot caliper, double
pivot caliper and vee brakes on the same bike at one time or another
and it seems to me that the determining factor, brake pad composition
aside, in braking power is the ratio between the brake arm, pivot to
cable attachment, and the arm on which the brake pad is mounted,
pivot to pad mounting, i.e,, the mechanical advantage of the brake,
and in reality nothing else seems to matter. The most powerful brakes
I ever had on that bike were cheap old vee brakes which, mounted on
the previous canti lever studs, had the brake pad at the lowest
possible position on the brake arms and thus the highest mechanical
advantage between the cable attachment and the pad.

Note that brake arm length and ratio also effect the cable pull
necessary to apply the brakes and I am talking about only the
effectiveness of the brake itself. And the brake levers themselves
have a mechanical advantage that will also effect braking.

While I never installed disc brakes on that bike I have brake tested
bikes with discs and if the ability to stop the wheel from turning is
a measurement of braking efficiency then any of the more efficient rim
brakes were equal in braking efficiency to the discs.

This exactly my experience as well over various brakes. You have to go
some way to get bad braking, it's usually the setup. Well setup rim
brakes work as well as discs, but imho, there are other reasons for
moving to discs. Half of my bikes are disc, the other half lack bosses
or they would be, but not for reasons of braking power except may be in
wet, and definitely in ice, but I don't cycle in icing conditions much.

A friend bought a second hand bicycle solely as transportation in a
very large yacht marina - he does mechanical maintenance on yachts -
and tells me one day that "I'll never buy another disc brake bicycle!"
I, having read all the users extolling discs on this site say, "How
come?" He says, "Cause they squeak all the time."
--
cheers,

John B.