Chalo Colina writes:
>> ...sidepull brakes have the pad pivot above and only slightly (rim half width) offset from the
>> braking surface so that there is essentially no position change as the pad sweeps through its
>> wear life (cosine error). Centerpull and cantilever brakes approach the rim at nearly a 45 degree
>> angle and have large vertical change throughout pad wear life,
> This trait of stud-mounted brakes can be accommodated by adjusting the pad height as it wears. The
> pad rub on tire sidewalls exhibited by single-pivot sidepulls, however, is due to the extreme
> fore-to-aft flex these brakes display and can not reliably be adjusted away.
You keep talking about cheap no use brake calipers. We've been riding on Campagnolo and Shimano
brakes for a long time and those who insist on using flimsy brands out to switch and atop talking
about ho bad these brakes were. Just the same, you seem to recognize that pad wear can cause
cantilever brakes to pop under the rim in dirt and wet conditions. It happens and it should be
apparent that the arc described by the pad attacks the rim at a 45 degree angle (large cosine error)
while a single pivot sidepull brake has a 5 degree angle, one that allows me to wear a Kool-Stop
Continental pad to the metal without adjustment.
> This horrible characteristic of single-pivot sidepull brakes is IMO one of the reasons for the
> annoying move to "short reach" road calipers-- because the stubby arms of those brakes are
> somewhat resistant to allowing sidewall rub for most average-sized riders.
long (standard) reach Campagnolo Record brakes from the 1960's do not flex enough to distort the
wear pattern on the rim. They hold their position even when braking hard enough to raise the
rear wheel.
>> the centerpull goes into the tire as it wears and offers no advantages whatsoever.
> When mounted on frame studs, it offers vastly superior maximum stopping power to any caliper
> brake. I know this because I have bent many forks under the braking forces generated by U-brakes.
> Before applying stopping power like that, caliper brakes become so twisted out of shape that
> applying more cable tension does not result in more braking.
So? Who uses centerpull brakes... and why? They are dogs!
>> Flex in any part of the system eats up hand lever stroke.
> Insufficient stroke length can be addressed by using levers that pull more cable, and pulling them
> harder. However, the swinging flex endemic to all centerbolt-mounted brakes, and the torsional
> flex that is particularly pronounced in single-pivot brakes, act disproportionately to diminish
> the braking that can be applied regardless of how hard or how far the cable is pulled.
> The "ceiling" on stopping force resulting from flex-related distortion of the brake mechanism is
> lower, and more abrupt, with single-pivot calipers than with any other type of brake.
Not on high quality calipers. You haul out discarded brake brands and types that have had no
business on bicycles in the last ten years.
>>> He notes that centerpulls don't stick out to the side like sidepulls.
>> How far??? What is the issue here anyway.
> I have seen enough bikes damaged by the sidepull brake arm bashing into the downtube to think of
> that design characteristic as a liability.
I've seen bicycle damaged by letting them fall over onto a curb. So what if there are oafs around
who can damage a bicycle. As I recall in a crash, both center and side pull brakes have gotten
dinged by or dinged the down tube.
>>> He says that even the standard-reach (what would be called long-reach by most) dual-pivot brakes
>>> offered by Shimano don't leave much room for fenders. Is that true?
>> NO.
> It is true if you wish to run decent-sized tires and fenders at the same time. Even the most
> careful brake placement will not allow "standard reach" dual-pivot calipers to encompass 38mm
> tires with fenders.
Long ago, split fenders were mad to not compromise the brake for fenders. The front half begins
ahead of the fork, the rear behind. I don't see this if it is racing bicycles we are talking about.
>> The sidepull brake is the obvious mechanism for road bicycles to all who understand mechanical
>> design. All this other stuff is amateur thinking guided by misunderstanding of the concept.
> Sorry, but that's just not true. It might be "the obvious mechanism" if one is unconcerned about
> generating the most stopping force from a given amount of brake, and if one disregards the
> benefits of voluminous tires, and if one happily tolerates pad rub due to a brake design that can
> not be centered accurately. But most "who understand mechanical design" demand (or at least
> desire) better performance than that!
How much do you need? I often think of that as I overtake riders descending steep roads. Riders who
are using all sorts of demonstrative cornering techniques as they pour on the brakes early into
turns. I suppose for these folks more brake force is necessary.
> Getting the brake pivot as close as practicable to the pads pays huge dividends in turning lever
> force into stopping force.
I'm sure you meant that differently than it came out. The shorter the brake arms the greater the
angular sweep in its stroke and the greater the cosine error involved in pad wear gets. The amount
of flex in the levers is the measure of performance at any given mechanical advantage. Of course
we've been at mechanical advantage before. It can be only so large that hand lever travel is not
used up by the time the pads make contact, that is pad clearance dictates mechanical advantage
upper limits.
> That very translation is exactly where single-pivot calipers are so weak. They only provide an
> approximately linear relationship between lever force and braking force up to a point-- a point
> easily exceeded by many riders in many circumstances.
Not so. Many riders have such weak hands that they could not adequately brake with 4:1 brakes that
were standard before dual pivot calipers came along. You may recall the old saw of "Campagnolo
Brakes are for racing and racers only need to modulate speed, not stop!" I heard it often enough to
gag. It's tough when you can't tell the customer he is a wimp and should develop more grip. So
there we have
it. Dual pivot! The brake that absolutely centers and can operate with minimal pad clearance. Up
the ME! By the way, the ME is so high that you cannot wear the pads to the metal, there being
insufficient adjustment at that level.
> Add to this the inherent characteristic of them being impossible to center consistently, and it's
> not at all obvious that they are superior to the worst of other brake designs, let alone the best
> of them.
That is true, but how accurately do you need it. I've been using them for many years and add a bit
of oil when they go off center in the rain.
>> Now let's hear it again concisely. What are the advantages?
> Concisely? Stopping. Centering.
Well that is what single pivot Campagnolo brakes do for me.
Jobst Brandt
[email protected]
