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.

--
- Frank Krygowski