Front brake caliper on the back of a fork

On Apr 1, 4:51*pm, Frank Krygowski wrote:
On Apr 1, 7:51*am, James wrote:









On Apr 1, 1:25*pm, User Bp wrote:

James wrote:

Bob, I would leave it the way it is, and simply cut a slot in the fender
and possibly fashion a bit of PVC or similar to cover the whole shebang.

Or do something like this...

http://www.flickr.com/photos/55102679@N05/5878886758

That is a most interesting setup, not least because it exactly matches
the layout I wanted... But, in your case it's on the rear, and I need
to deal with the fork.

Very neat work, thank you for sharing the picture. What dynamo is shown?

The dynamo is a Sanyo Dynapower, from the late 80's I think. *I
resurrected it and built a headlight from 4 CREE LEDs. *It works a
treat with the LEDs, but it had a habit of blowing globes which is why
I'd stopped using it. *I tested it recently and found the output is
not self regulated to a low enough level to safely power incandescent
bulbs. *It would need some form of protection (zener diodes for
example) for that.

I just dug out my old notes from testing some dynamos when I was first
trying to learn about them. *That was the first one I tested, by just
putting a standard AC voltmeter across it and taking voltage vs. speed
readings with the bike on a workstand. *Anyway, I took voltage values
with a few different loads, and I see I was having some trouble,
because I got inconsistent readings in come cases.

The resistance of a wire(or filament/element) falls as it heats.
Temperature changes lag supply changes that need to be accounted for.
Your tests did not allow for the system to stabilise between taking
readings. There is consistency if one plots the complete
stabilisation time. A blower is also required to effect a cooling
wind on the lamp unit. Metal cased lamps are better protected from
blackening or burnout. Of importance is the correct oriemtation of
the filament. Unfortunately some holders were fixed so that a screw-
in filament was not correctly installed with the element level.


But speaking of blowing bulbs, when I tested it with a Union halogen
headlight plus incandescent taillight, I got an indicated 7.25 VAC at
20 mph.

Easily safe. IIRC something like an indicated 10V a.c. was
acceptable with good quality 6 d.c. rated bulbs.

*But when I tried it with the headlight alone, it blew the
bulb at 16 mph!

The world around. With a single bulb, go for a higher voltage at
similar current rating or go for a higher current at the nominal
system voltage. Easy solution is to choose the bulb current which
matches the dynamo output at the nominal voltage also choosing th bulb
to match the nominal voltage..


So my bench test experience matches James's on-bike
experience. *(On my bike, I always used it with an incandescent
taillight, and it was fine. *Except it had lower output at low speeds
like 6 to 8 mph than most other dynamos. *I remember that annoying me
when I was riding my bike slowly around some campgrounds.)

Use two headlamps, one with a widespread beam for low speed and tight
bends which is on continuopusly at night and switch the second in at
higher speeds for a narrow long range beam.

The other interesting point about that dynamo is that its output (on
an oscilloscope) doesn't look anything like a sine wave. *All the

Ah, that'll explain their tendency to slip, not just a wet tread.

others I tested were basically sinusoidal, perhaps with a bit of a
harmonic. *That means my primitive AC meter would probably not have
been giving accurate RMS values. *I later borrowed a true-RMS meter
for testing other dynamos, but I never re-tested the Sanyo.

- Frank Krygowski

On Apr 1, 1:45*pm, thirty-six wrote:


The resistance of a wire(or filament/element) falls as it heats.

Oh? Table 1 at http://hypertextbook.com/facts/2004/DeannaStewart.shtml
seems to suggest otherwise.

Most of the reminder of your post was of similar quality.

- Frank Krygowski

On Apr 3, 1:16*am, John B. wrote:
On Fri, 30 Mar 2012 03:42:35 -0700 (PDT), thirty-six









wrote:
On Mar 30, 12:37*am, James wrote:
On 30/03/12 09:37, Joe Riel wrote:

Phil W *writes:

User *considered Thu, 29 Mar 2012 04:28:42 +0000
(UTC) the perfect time to write:

I'm interested in moving the front brake caliper from the front of the
fork to the back. It's an old-fashioned Shimano 600 setup, far from
high tech but adequate for my riding. The motive is a little convoluted:
A roller dynamo is hanging on the caliper mount bolt, at the back.
A fender would be highly desirable, but is obstructed by the dynamo
(but not by a brake). If it were possible to "turn things around" so
the caliper was in back and the dynamo was in front a fender would fit.

It's clear the caliper reach would be longer and the angle to the
wheel different. Does anybody know if this can (or can't) be done
successfully?

Thanks for reading,

bob prohaska

You do realise that this has serious safety implications?
The caliper being on the front means that reaction forces hold the
front axle into the dropout, whereas if you move it to the rear, the
reaction forces will be attempting to eject the front axle from the
dropout.
A sensible safety standard would outlaw rear mounted front brake
calipers.

On the other hand, the stress in the retaining bolt is now
compressive, so is less likely to suffer fatigue induced
fracturing. *Especially with cut rather than rolled threads.

Fun times...

What about bending stress? *Wouldn't it just be reversed (down instead
of up)?

How tight is the centre bolt to begin with?

Tight enough to stop the mounting boss parting from the fork crown due
to leverage applied by the brake arms. *The pure pulling force
parallel to the mounting bolt is relatively minor. *Even with a racing
brake caliper, the ratio is 5:1 * Braking force at the caliper may go
above the mass of rider when braking hard in the bends so a force of
200lbs at the brake shoe should be expected. *As this is amplified 5
times at the brake boss, the pull will be 1000lbf at the bottom of the
boss and so 2000lbf is required on the bolt itself to prevent the boss
from moving under heavy braking.

Err... Not foot pounds; that is a measurement of torque. what you are
trying to measure is simply the necessary tensile strength of the
bolt.
Pressure, in lbs imposed on brake X moment = *total force imposed on
brake bolt. Translate that to PSI and you have the absolute minimum
strength needed for the brake bolt.
--
Cheers,

John B.

lbf - pounds force, distinguishing it from lb(s), a unit of mass.

On Apr 3, 1:24*am, John B. wrote:
On Fri, 30 Mar 2012 10:14:21 -0700 (PDT), thirty-six









wrote:
On Mar 30, 6:00*pm, Tom Ace wrote:
On Mar 30, 9:38*am, Frank Krygowski wrote:

On Mar 30, 12:12*pm, Tom Ace wrote:

I've put the rear brake on the front side of the bridge
on all the frames I've had that permitted it, e.g.
* *http://minortriad.com/prime/brake.jpg

What do you see as the advantage?

I like how it looks.

Tom Ace

Did you weight that up against the disadvantages?

What disadvantages do you see?

--
Cheers,

John B.

Snide commentry, or should that be wrong side componentry. :-)

Sir Ridesalot wrote:

Depending on which era your 600 caliper is from you'll have trouble
turning to one side. In fact I just offered up my old 600 Areabesque
caliper to a front fork and it looks like a turn to the right would
only allow the fork to roatate a couple of degrees. I think you're far

This might be the blow that "hits the nail on the thumb" 8-) The brake
cable will foul the downtube. I've seen calipers where the cables
go down instead of up, but that means a new caliper assuming one can
be found.

I should have seen this coming but did not. Thanks for pointing it out.

bob prohaska

On Tue, 3 Apr 2012 18:27:02 -0700 (PDT), thirty-six
wrote:

On Apr 3, 1:16*am, John B. wrote:
On Fri, 30 Mar 2012 03:42:35 -0700 (PDT), thirty-six









wrote:
On Mar 30, 12:37*am, James wrote:
On 30/03/12 09:37, Joe Riel wrote:

Phil W *writes:

User *considered Thu, 29 Mar 2012 04:28:42 +0000
(UTC) the perfect time to write:

I'm interested in moving the front brake caliper from the front of the
fork to the back. It's an old-fashioned Shimano 600 setup, far from
high tech but adequate for my riding. The motive is a little convoluted:
A roller dynamo is hanging on the caliper mount bolt, at the back.
A fender would be highly desirable, but is obstructed by the dynamo
(but not by a brake). If it were possible to "turn things around" so
the caliper was in back and the dynamo was in front a fender would fit.

It's clear the caliper reach would be longer and the angle to the
wheel different. Does anybody know if this can (or can't) be done
successfully?

Thanks for reading,

bob prohaska

You do realise that this has serious safety implications?
The caliper being on the front means that reaction forces hold the
front axle into the dropout, whereas if you move it to the rear, the
reaction forces will be attempting to eject the front axle from the
dropout.
A sensible safety standard would outlaw rear mounted front brake
calipers.

On the other hand, the stress in the retaining bolt is now
compressive, so is less likely to suffer fatigue induced
fracturing. *Especially with cut rather than rolled threads.

Fun times...

What about bending stress? *Wouldn't it just be reversed (down instead
of up)?

How tight is the centre bolt to begin with?

Tight enough to stop the mounting boss parting from the fork crown due
to leverage applied by the brake arms. *The pure pulling force
parallel to the mounting bolt is relatively minor. *Even with a racing
brake caliper, the ratio is 5:1 * Braking force at the caliper may go
above the mass of rider when braking hard in the bends so a force of
200lbs at the brake shoe should be expected. *As this is amplified 5
times at the brake boss, the pull will be 1000lbf at the bottom of the
boss and so 2000lbf is required on the bolt itself to prevent the boss
from moving under heavy braking.

Err... Not foot pounds; that is a measurement of torque. what you are
trying to measure is simply the necessary tensile strength of the
bolt.
Pressure, in lbs imposed on brake X moment = *total force imposed on
brake bolt. Translate that to PSI and you have the absolute minimum
strength needed for the brake bolt.
--
Cheers,

John B.

lbf - pounds force, distinguishing it from lb(s), a unit of mass.

A yes, the pound-force. Equal to the gravitational force exerted on a
mass of one avoirdupois pound on the surface of Earth.
--
Cheers,

John B.

On Tue, 3 Apr 2012 18:28:22 -0700 (PDT), thirty-six
wrote:

On Apr 3, 1:24*am, John B. wrote:
On Fri, 30 Mar 2012 10:14:21 -0700 (PDT), thirty-six









wrote:
On Mar 30, 6:00*pm, Tom Ace wrote:
On Mar 30, 9:38*am, Frank Krygowski wrote:

On Mar 30, 12:12*pm, Tom Ace wrote:

I've put the rear brake on the front side of the bridge
on all the frames I've had that permitted it, e.g.
* *http://minortriad.com/prime/brake.jpg

What do you see as the advantage?

I like how it looks.

Tom Ace

Did you weight that up against the disadvantages?

What disadvantages do you see?

--
Cheers,

John B.

Snide commentry, or should that be wrong side componentry. :-)

Not at all. I am contemplating mounting a brake in that manner and see
no disadvantages, thus my question.
--
Cheers,

John B.

On Apr 4, 6:45*pm, John B. wrote:
On Tue, 3 Apr 2012 18:28:22 -0700 (PDT), thirty-six
Snide commentry, *or should that be wrong side componentry. *:-)

Not at all. I am contemplating mounting a brake in that manner and see
no disadvantages, thus my question.

Some brake bridges accept recessed
allen-head nuts on one side only. The pic at
http://minortriad.com/prime/brake.jpg
shows a custom frame where I'd asked for the
bridge to be installed the opposite of usual.

If you're happy with the way the brake mounts
on your frame and with how the cable runs,
I see no reason not to do it.

Tom Ace

On Apr 5, 2:45*am, John B. wrote:
On Tue, 3 Apr 2012 18:28:22 -0700 (PDT), thirty-six









wrote:
On Apr 3, 1:24*am, John B. wrote:
On Fri, 30 Mar 2012 10:14:21 -0700 (PDT), thirty-six

wrote:
On Mar 30, 6:00*pm, Tom Ace wrote:
On Mar 30, 9:38*am, Frank Krygowski wrote:

On Mar 30, 12:12*pm, Tom Ace wrote:

I've put the rear brake on the front side of the bridge
on all the frames I've had that permitted it, e.g.
* *http://minortriad.com/prime/brake.jpg

What do you see as the advantage?

I like how it looks.

Tom Ace

Did you weight that up against the disadvantages?

What disadvantages do you see?

--
Cheers,

John B.

Snide commentry, *or should that be wrong side componentry. *:-)

Not at all. I am contemplating mounting a brake in that manner and see
no disadvantages, thus my question.
--
Cheers,

John B.

I meant snide comments from other riders may be considered a
downside. As it's another day I've had another thougth this week, it
must be tuesday. When mounting a brake opposite to normal, it is
going to be more dificult to centre or service unless you first check
you have suitable tools to fit in the restricted space. I liked to
use a long cone spanner (Cobra brand) to accurately centre the brake
pads, the short ones didn't give enough hand clearance with the brakes
in the regular direction, with them wrong way it'll be even more
difficult and you then need to make, purchase (if you can find) or
adapt (by thinning) a right angle flat spanner. Servicing of the
caliper arm pivot(s) in-situ becomes practically impossible Racing
brakes face the ends of the bike for servicing speed, but in other
cases you might not see this as significant.

On Wed, 4 Apr 2012 19:59:40 -0700 (PDT), Tom Ace
wrote:

On Apr 4, 6:45*pm, John B. wrote:
On Tue, 3 Apr 2012 18:28:22 -0700 (PDT), thirty-six
Snide commentry, *or should that be wrong side componentry. *:-)

Not at all. I am contemplating mounting a brake in that manner and see
no disadvantages, thus my question.

Some brake bridges accept recessed
allen-head nuts on one side only. The pic at

shows a custom frame where I'd asked for the
bridge to be installed the opposite of usual.

If you're happy with the way the brake mounts
on your frame and with how the cable runs,
I see no reason not to do it.

Tom Ace

Nor do I. Thus my question :-)
--
Cheers,

John B.