From: etxorst@eos.ericsson.se (Torsten Lif)
Subject: Re: What's the theory behind Force 40 brakes?
Reply-To: etxorst@eos.ericsson.se
Organization: Ericsson Telecom AB
Date: Fri, 2 Oct 1992 08:21:29 GMT

In article 6610@blue.cis.pitt.edu.UUCP, jwgst2+@pitt.edu (James W Gourgoutis) writes:
>
>	What's the theory behind Cannondale's Force 40 brakes?  I've recently
>seen them on my friend's Cannondale, and it seems relatively simple.
>	I was thinking of converting my cantilevers on my MTB to this style
>of brake.  Can it be done?  How so?  Is it worth it?
>	Please advise.  Thanks!

On a "normal" cantilever setup you have an anchor for the cable houring
and the inner cable then pulls the straddle cable straight up like
this (just like on an old "centerpull" caliper brake):


                                !|!
                                !|!
                                !|!
                                 |
                                 |
                                 |
                                 |
                                / \
                               /   \
                              /     \
                             /       \
                            /         \
                           /           \
                           \           /
                            \P       9/


The "P" and "9" are crude ASCII-graphigs for the pads (sorry).

Anyway, on a Force 40 system, the cable housing is not anchored to the
frame. Instead it is attached to the straddle cable which in turn runs
over an idler pulley (the "O" below):


                                    !|!
                                    !|!
                                /O\ !|!
                               /   \!|!
                              /     !|!
                             /        \
                            /          \
                           /            \
                           \            /
                            \P        9/


Cannondale's marketing have told you this is to improve braking
performance. That's a lie. Sure, it does give greater leverage since
the mechanical advantage of the brake is changed. If the angles above
are all straight (90 degrees is hard to do in ASCII), the difference is
the infamous sqrt(2) or 41.4 % which is where the "40" crops up. But if
a different leverage was really desired, the brake manufacturers could
have implemented it years ago by changing the levers. No, the real
reason behind this design is that it's an easy and compact way of
anchoring the cable housing on a suspended bike. Other manufacturers
have to resort to all sorts of yokes and bridges to provide somewhere
fixed for the housing. On a Force 40 bike it runs just like on a
sidepull caliper brake. Neat. But you will not catch marketing
admitting that a change like that was to make life easier for their
engineers. Instead they focus on the changed leverage and tout it as a
big plus.

I have built a system like this on my recumbent (which is folding and
thus has the same problems with where to anchor the cable housing) and
it does work but the disadvantages are exactly what you might expect.
Since pad force is 40 % greater, movement is 30 % (1/sqrt(2)) smaller.
Thus, the pads need to be adjusted to ride VERY close to the rim at all
times and the rim has to be perfectly straight (in true). C'dale riders
have testified to problems in mtb racing when they've dinged their
wheels. A slight wobble in the wheel that would previously not have
been a hindrance will rub the brake pads on a Force 40 system. For a
person riding in a hurry under adverse conditions (mtb racing) this can
be a disaster. If you don't race but have the time to stop and true
your wheel immediately if it gets damaged, or at least to loosen up the
brake cable so you can limp home with less braking capacity, the Force
40 system works nicely and can save a bit on hand strain.

If you want to convert your brakes, this can be done quite simply if
you can get the Cannondale spare parts for the idler pulley and the
little bracket that goes on the straddle cable. Or, if you're skilled
with tools, you can plagiarize them easily enough using other standard
spares. The latter will probably not look quite as good, though. At
least, it doesn't on my 'bent. :-)

---
 Torsten Lif                          |   "No, there's nothing wrong
 Ericsson Telecom AB, EO/ETX/TX/AD    |    with my bike."
 S-126 25  STOCKHOLM, SWEDEN          |   "It's just a little 'bent."
 Tel: +46 8 719 4881                  |