From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech,rec.bicycles.misc,rec.bicycles.marketplace
Subject: Re: Drop bolts for Dual-Pivot Brakes
Date: 14 Aug 2000 15:17:21 GMT

Sheldon Brown writes:

>>> Just got some in!  For pix and more details, see:
>>>      http://sheldonbrown.com/harris/brakes.html#dropbolts

> A gloomy Gus wrote:

>> Looks spooky to me.  What sort of press fit retention is that in
>> the drop piece.  As you may recall, Campagnolo made them of one
>> piece forgings.  My life hangs on that little screw and I don't see
>> that it is safely anchored.  There may be more than meets the eye,
>> but I doubt it.

> Jeez, you gotta assume the worst!  I checked with the vendor, and,
> as I suspected, the stud is threaded into the block, then tack
> tig-welded.

It's worse than that.  Only with a press fit would the integrity of
the bolt be assure but to do that it would have to be pressed in from
the back side and have a small retention shoulder.  The brake bolt is
a critical part not to be taken lightly.  It supports some substantial
bending loads that in the threaded design you seem to have are not
being addressed because both extensions have threads at their root.
Threads reduce the bending cross section by about half and to top that
off, have a notch effect.  You'll notice that a regular brake bolts do
not have threads in the bending zone but at the retention ends where
they are only in tension.

What is less apparent is that a caliper that separates from the fork
crown will lock onto the wheel and cause a front wheel lock-up.  To be
appreciated, this should be tried in the bike shop by removing the
retention nut on the back of the fork crown.  The caliper detaches
from its position but remains on the wheel, canting as it goes because
the cable restrains it and locks it onto the wheel.

The common perception is that the brake separates and flies off the
front end, which of course is not the case.  Again, I repeat that the
drop bolts made by Campagnolo were forged of one piece for good cause.
This is not a trivial piece of hardware.  I would not like to answer
for a failure of a threaded one in court.  Under heavy use, failure is
predictable.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech,rec.bicycles.misc,rec.bicycles.marketplace
Subject: Re: Drop bolts for Dual-Pivot Brakes
Date: 14 Aug 2000 20:30:08 GMT

Sheldon Brown writes:

> This is by no means universally true.  There are millions of brakes
> in use that have full length threading.  Look at any English
> 3-speed.  These brakes also have much longer arms than the short
> dual-pivots, so the bending load is correspondingly greater, even
> though the braking power may be somewhat less.  I've never seen one
> of these bolts break, though lots of 'em get bent in crashes--and
> I've been working on these bikes for a LONG time.

We're talking brakes here that people use to descend mountain roads,
brakes on which the bicycle more or less stands on its front wheel
entering a turn.  When descending such roads with a clear view of the
valley, straight below, you don't want to be riding the clunky brakes
you describe.  I've seen this stuff fail and heard the amazement of
the bike shop folks.  As my friend who built my bike said as we
descended the Stelvio, "It's moments like this that I think of all the
first time frame builders (and others) who have never faced the
reality of their work and have no concept how fatally it might fail."

As I said, Tullio didn't make them of one piece for idle expensiveness.

Jobst Brandt      <jbrandt@hpl.hp.com>