Jobst Brandt wrote:
> Centerpull are self contained cantilevers and both suffer from large cosine error, the pivot
> points being on a nearly 45 degree axis from pad contact... dogs!
>
>
http://draco.acs.uci.edu/rbfaq/FAQ/8f.15.html
The popularity of centerpull calipers was in a time when most rims had angled braking surfaces, as
opposed to the parallel braking surfaces that are now the norm.
For such rims, the cosine "error" of centerpull calipers (or "U brakes") is actually a feature!
I had reminisced:
>>However, if you're speaking of modern dual pivot sidepulls, the earliest ones I know of were made
>>by Altenburger in the late '60s.
> Yes, but they did not take advantage of the lower pad clearance possible with centered brakes.
> They didn't see the need and were to timid to diverge from the standard 4:1 mechanical advantage
> of the day.
>>They were generally considered slightly inferior to the popular centerpull calipers of the day
>>from Mafac, Weinmann, Universal and GB.
> That was a bunch of marketing. I chucked the centerpulls immediately and switched to Universal
> side pulls before Campagnolo brakes were generally available. Centerpull brakes were duds right
> from the start but were touted to have greater stopping power because they had twice the force...
> a complete lie. They had 4:1 like all brakes of the day.
The Universals were very nice calipers indeed. However, I believe that comparing '60s and '70s
centerpulls with garden variety long-reach sidepulls, as fitted on "sport-touring" tenspeeds of the
era, the centerpulls generally had a higher mechanical advantage, at least when properly set up.
>>The superiority of modern brakes has much more to do with improved levers, cables and shoes than
>>it does with caliper design.
> It has only one feature and that is a higher mechanical advantage. The short arm on the offset
> pivot has significant cosine error (foreshortening caused by angular motion. A conventional side
> pull brake operating at less than 5 degrees has less than 4% vertical motion of the pad from new
> to worn to the metal. No other mechanical lever brake can be operated for the life of the pad
> without adjustment.
That generalization has been invalidated by the move to thinner pads! It also doesn't apply to
centerpulls used with angled rims, nor to various brake types used with rims with a tall braking
surface, such as the (yuck!) Weinmann concave.
> The pad position on my old Campagnolo brakes never need adjustment. Only cable slack from pad wear
> need be taken up and it can do that as well.
This feature is certainly of some value, but it isn't overwhelming. Not all cyclists have as strong
hands as you do, and some of us with weak hands find old Campagnolo sidepulls highly unsatisfactory.
Sheldon "Current Campag Brakes Are Fine" Brown +----------------------------------------+
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| | --Damon Runyon |
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