On 1/31/2020 5:31 PM, Tim McNamara wrote:
On Thu, 30 Jan 2020 15:11:15 -0800 (PST), Sir Ridesalot
wrote:
On Thursday, 30 January 2020 17:18:31 UTC-5, Tim McNamara wrote:

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.

I haven't used those but I did put old school Alivio V-brakes on my
dropbar MTB with Tecktro dropbar V-brake levers and I find the braking
FAR superior to what I had with my cantilever brakes. This is even
more so in snow or rain.

Makes sense for a few reasons. One, there is no straddle wire. Two,
the mechanical advantage is greater than almost all if not all
cantilevers (close to that of centerpulls). Three, the cable approach
to the brake is smooth with wide radius bends. Four, unlike cantis the
brake arms don't jut out from the frame quite so much.

I'm not sure what Sir meant by "braking FAR superior..." to cantilever
brakes - or for that matter, to other brakes. "Good braking" seems
nebulously defined.

And I'm not sure what Tim meant when characterizing the lack of a
straddle wire as a benefit. I don't see any great detriment in a
straddle wire, especially if it's set up correctly.

I think a lot of people perceive "better braking" to mean "more
deceleration from a given hand squeeze on the lever." OK, let's examine
that. The bulk of it is simple mechanical advantage - that of the lever
plus that of the brake itself.

Is more mechanical advantage better? Not necessarily. It comes with the
built-in disadvantage of less pad or shoe travel, meaning it can
tolerate less crookedness in the rim, disc, drum or whatever. IOW you
pay for it when your disc squeaks or your rim brake scrapes when JRA.
Tim mentioned this.

But the other disadvantage is hypersensitivity. People do crash from
over-braking, and ISTM the less lever force required, the easier that
mistake is. I prefer to have to squeeze moderately hard to decelerate
moderately hard. For mountain biking where long super-steep descents are
common, super-low lever force may be nice; but otherwise, perhaps not.

Different brake designs do have different mechanical advantages, but
people sometimes guess wrong about those MAs. I haven't run the numbers
for a long, long time (I once gave those as a project to a student
wanting some advanced credit for a course) but ISTR Jobst pointing out
that, contrary to myth, centerpulls don't have more MA than normal
sidepulls. (We can discuss.) Shimano upped the MA with dual pivot, but
that did require truer wheels. They upped it again with V-brakes, and
had to compensate by reducing the MA of the levers, making almost all
levers incompatible, as Tim said. (I sometimes think Shimano has a very
large Department of Incompatibility.)

I'll admit, though, that high MA in the brake itself may confer a couple
of secondary advantages. It means less tension in the cable, and less
tension means less friction loss. I think it was also Shimano that
started the practice of return springs in the lever as well as the
caliper. That allows a lighter caliper spring (since the caliper's not
dragging the cable) and a little less hand squeeze. But I think those
benefits are very small, unless a person has really cruddy cables.

Another factor affecting braking force from a given lever squeeze is the
choice of shoe or pad material. Are there rim brake pads better than the
Salmon ones? If I had brake problems and didn't use Salmon pads, that's
the first thing I'd check.

There are other secondary or detail considerations. I agree, I don't
like the fact that classic L-shaped cantilevers protrude so much. I've
switched to low profile ones except on my mountain bike, where that
doesn't matter.

I think one big reason for direct pull V-brakes taking over from other
cantilevers is that they don't require a cable stop on the frame. That
cable stop required some real kludging when mountain bikes switched to
suspension forks. Direct pulls solved that handily. Other than that, I
don't see significant differences in cable routing (or bends) between
the two. Actually, a flat-bar bike gets about 90 degree bend for a
normal canti, vs. about 180 degrees for a direct pull.

Everything is trade-offs.

That's certainly true. But aside from weirdnesses like Campy Delta or
Roller Cams, these non-hydraulic things are just lever systems.
Designers just dial in the desired MA, try to reduce flex and friction,
and keep things out of the way.

BTW, it's fun to browse through The Data Book and other historical
documents to see what's been done with brakes. There's been lots of
tinkering over the decades. And I'm sure that every design is better
than every other design - at least, in someone's eyes.


--
- Frank Krygowski