Re: x-post: Bike Biz: Wheel ejection theory goes legal



On 16 Feb 2007 11:29:38 -0800, [email protected] wrote:

>On Feb 16, 12:41 am, [email protected] wrote:
>> On 15 Feb 2007 20:04:07 -0800, [email protected] wrote:
>>
>>
>>
>> >On Feb 15, 6:46 pm, Tim McNamara <[email protected]> wrote:

>>
>> >> Under ideal circumstances, jim's assessment that the retention provided
>> >> by the QR should exceed the ejection force is probably reasonable. But
>> >> non-ideal circumstances are all too readily encountered in real life.

>>
>> >Jim seems to think a retention force three times the ejection force
>> >(IF everything is done perfectly) is obviously adequate.

>>
>> >In other words, he's satisfied with a design factor (or safety factor)
>> >of three.

>>
>> >But in mechanical design, all common parts are always designed with a
>> >safety factor. That is, parts are not designed to be precisely as
>> >strong as necessary. If that were done, then any tiny error in
>> >evaluation of force, material property, manufacturing technique, or
>> >operating condition would cause failure.

>>
>> >For ordinary industrial design using well-known materials, well
>> >understood loads, ordinary controlled conditions of operation, etc.
>> >safety factors of three are quite common.

>>
>> >For situations where adjustments have to be made in the field by
>> >operators using their own feel and judgement, where loads are
>> >difficult to assess, and where failure can result in serious bodily
>> >harm, a safety factor of three is entirely inadequate.

>>
>> >> Since the fork can be readily redesigned to eliminate the ejection
>> >> force, there is no reason not to do it- and is already being done to a
>> >> degree by the fork makers.

>>
>> >Exactly.

>>
>> >- Frank Krygowski

>>
>> Dear Frank,
>>
>> What is an entirely adequate safety factor "for situations where
>> adjustments have to be made in the field by operators using their own
>> feel and judgement, where loads are difficult to assess, and where
>> failure can result in serious bodily harm"?
>>
>> Possibly rock climbing equipment will give some insight?

>
>Try http://www.usrigging.com/SafetySnapHooks.pdf for one example.
>
>And note that with these, there's no fiddling with a screw adjustment
>to achieve proper strength. There's no chance of a partial
>engagement, by design. But there's still a safety factor of ten.
>
>- Frank Krygowski


Dear Frank,

Interesting.

I looked at climbing ropes (the weakest link).

Here's a description of the rope tests:

"The Union Internationale des Associations d'Alpinisme (UIAA)
certifies climbing equipment. The manufacturer pays dearly to have its
products certified but, because of its rigorous testing, UIAA
certification is a guarantee of high quality. One test determines the
number of falls the rope can withstand with a load of 80 kg (55 kg for
half ropes) before breaking. The length of rope used in the test is
approximately 2.8 m. The weight, attached to one end of the rope, is
released from a height of 5 m. This test simulates a severe fall over
twice the distance between the climber and his or her last piece of
protection. The impact force is also very high since, in the
relatively short length of the fall, the rope's elasticity does not
particularly come into play."

"The impact force test verifies whether a rope's elasticity meets
minimum standards. Ropes have a certain measure of elasticity so that
they can absorb and dissipate the force of impact. If the rope is too
elastic, the climber will bounce uncontrollably after a fall, with
disastrous results. Impact force is measured in the first fall in the
test described above. The impact force must be less than 1200 kN (800
kN for a half rope). So, practically speaking, the smaller the impact
force indicated on the manufacturer's label, the more the rope will
absorb energy in a fall and minimize the impact on your belay system."

http://www.lacordee.com/en/conseils/details/achat/?id=18

And here's a page with some actual ropes and ratings:

http://www.metoliusclimbing.com/ropes_dynamic.htm

If you browse around, you'll notice that there's another extremely
interesting test--the number of UIAA sharp edge falls that the rope
can withstand.

The maximum on that page is 1 such fall for any rope. Apparently, if
you fall and let your rope hit a sharp edge on the mountain, all the
other safety factors are not going to be very helpful.

Cheers,

Carl Fogel
 
Debacle writes:

>> Caster is called "trail" on bikes: it's the distance from the
>> projection of the steering pivot to the contact patch in the
>> forwards axis (not the sideways axis, which is scrub).


> Is it really? Wouldn't caster for a car correspond to head tube
> angle for a bike?


There are dimensions called caster angle and caster trail on cars and
other industrial vehicles. As usual, the bicycle folks, being quick
to pick up jargon, regardless of understanding what it means, have
given these words so many interpretations that it will give anyone
listening a snow-job. In the bicycle business "rake" is often taken
to be "trail".

see: http://www.m-w.com/dictionary/rake

click on: rake(3)

Ben C? should not spread his rumors with such dogmatic certainty,
considering he doesn't understand auto steering geometry.

Jobst Brandt
 
Ben C? writes:

>>> Caster is called "trail" on bikes: it's the distance from the
>>> projection of the steering pivot to the contact patch in the
>>> forwards axis (not the sideways axis, which is scrub).


>> Is it really? Wouldn't caster for a car correspond to head tube
>> angle for a bike?


> This is something I've never been 100% clear about.


> People talk about trail on bikes, not caster. AIUI trail is the
> offset from the projection of the head tube (which is the steering
> pivot) onto the ground back to the contact point of the tyre.


> Trail is a function of head tube angle, but also of fork
> rake. Increase fork rake and you reduce trail for a given head tube
> angle.


OK, how about defining rake and its effect on trail instead of tossing
out vague references. Keep in mind the definition given in English:

http://www.m-w.com/dictionary/rake

rake(3) being the one in question.

Jobst Brandt
 
A

A Muzi

Guest
> Debacle writes:
>
>>> Caster is called "trail" on bikes: it's the distance from the
>>> projection of the steering pivot to the contact patch in the
>>> forwards axis (not the sideways axis, which is scrub).


>> Is it really? Wouldn't caster for a car correspond to head tube
>> angle for a bike?

>

[email protected] wrote:
> There are dimensions called caster angle and caster trail on cars and
> other industrial vehicles. As usual, the bicycle folks, being quick
> to pick up jargon, regardless of understanding what it means, have
> given these words so many interpretations that it will give anyone
> listening a snow-job. In the bicycle business "rake" is often taken
> to be "trail".
> see: http://www.m-w.com/dictionary/rake
> click on: rake(3)
> Ben C? should not spread his rumors with such dogmatic certainty,
> considering he doesn't understand auto steering geometry.


I will plead guilty as charged for using 'industry jargon' over common
English.

In our industry, and I have two manufacturers' custom frame order forms
in front of me at the moment, fork offset is customarily called 'rake'
to distinguish it from 'head angle'.

A vertical line through the axle center to the ground falls behind the
extended centerline of the head tube at the ground. The distance between
those points is customarily our 'trail'. For bicycle purposes only.

A quick perusal of a dozen major manufacturer's catalogs for this and
last year shows no exceptions to these terms. For bicycles, that is.

We all understand that the auto world uses somewhat different
nomenclature. For our industry purposes these are the lingua franca of
the front end of a bike. They're useful and widespread, for bicycles.
Just not always useful in other areas.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
 
B

Ben C

Guest
On 2007-02-17, [email protected] <[email protected]> wrote:
> Ben C? writes:
>
>>>> Caster is called "trail" on bikes: it's the distance from the
>>>> projection of the steering pivot to the contact patch in the
>>>> forwards axis (not the sideways axis, which is scrub).

>
>>> Is it really? Wouldn't caster for a car correspond to head tube
>>> angle for a bike?

>
>> This is something I've never been 100% clear about.

>
>> People talk about trail on bikes, not caster. AIUI trail is the
>> offset from the projection of the head tube (which is the steering
>> pivot) onto the ground back to the contact point of the tyre.

>
>> Trail is a function of head tube angle, but also of fork
>> rake. Increase fork rake and you reduce trail for a given head tube
>> angle.

>
> OK, how about defining rake and its effect on trail instead of tossing
> out vague references. Keep in mind the definition given in English:
>
> http://www.m-w.com/dictionary/rake
>
> rake(3) being the one in question.


Someone previously posted this page, with a good diagram, which was what
I was thinking of:

http://www.kreuzotter.de/english/elenk.htm

and I'm glad to see I remembered the definitions of "trail" and "fork
rake" about right.

Google also retrieved this:

http://yarchive.net/bike/rake.html

"However, the bicycle usage seems to arise from believing the curl
in the conventional fork is reminiscent of the bias in a garden
rake, unaware that a rakish angle is a steep one and that rake IS
the term for fork angle. Bicycling is full of jargon that got
mangled in the care of mechanics who know that steel gets soft and
that tires need to age and develop cracks to be any good. It's time
to reverse some of these notions."

It seems I may have unwittingly touched another nerve.
 
B

Ben C

Guest
On 2007-02-17, [email protected] <[email protected]> wrote:
> Debacle writes:
>
>>> Caster is called "trail" on bikes: it's the distance from the
>>> projection of the steering pivot to the contact patch in the
>>> forwards axis (not the sideways axis, which is scrub).

>
>> Is it really? Wouldn't caster for a car correspond to head tube
>> angle for a bike?

>
> There are dimensions called caster angle and caster trail on cars and
> other industrial vehicles. As usual, the bicycle folks, being quick
> to pick up jargon, regardless of understanding what it means, have
> given these words so many interpretations that it will give anyone
> listening a snow-job. In the bicycle business "rake" is often taken
> to be "trail".


It seems that at least sometimes it's taken to mean something rather
different from that: fork offset.

See http://www.kreuzotter.de/english/elenk.htm
 
On Sat, 17 Feb 2007 02:16:37 -0600, Ben C <[email protected]> wrote:

>On 2007-02-17, [email protected] <[email protected]> wrote:
>> Ben C? writes:
>>
>>>>> Caster is called "trail" on bikes: it's the distance from the
>>>>> projection of the steering pivot to the contact patch in the
>>>>> forwards axis (not the sideways axis, which is scrub).

>>
>>>> Is it really? Wouldn't caster for a car correspond to head tube
>>>> angle for a bike?

>>
>>> This is something I've never been 100% clear about.

>>
>>> People talk about trail on bikes, not caster. AIUI trail is the
>>> offset from the projection of the head tube (which is the steering
>>> pivot) onto the ground back to the contact point of the tyre.

>>
>>> Trail is a function of head tube angle, but also of fork
>>> rake. Increase fork rake and you reduce trail for a given head tube
>>> angle.

>>
>> OK, how about defining rake and its effect on trail instead of tossing
>> out vague references. Keep in mind the definition given in English:
>>
>> http://www.m-w.com/dictionary/rake
>>
>> rake(3) being the one in question.

>
>Someone previously posted this page, with a good diagram, which was what
>I was thinking of:
>
> http://www.kreuzotter.de/english/elenk.htm
>
>and I'm glad to see I remembered the definitions of "trail" and "fork
>rake" about right.


[snip]

Dear Ben,

That diagram is worth a thousand words.

As usual, the wheels don't care about our lexicographical arguments.

As far as I can tell, anyone discussing rake and trail on RBT will be
most helpful if he explains in passing which meanings he has in mind
and move on to his real point about the effect of the geometry on
handling.

I cannot off-hand think of any common meaning that has been changed by
appeals to dictionary sub-headings.

Cheers,

S. Johnson
 
M

Michael Press

Guest
In article <[email protected]>,
[email protected] wrote:

> Ben C? writes:
>
> >>> Caster is called "trail" on bikes: it's the distance from the
> >>> projection of the steering pivot to the contact patch in the
> >>> forwards axis (not the sideways axis, which is scrub).

>
> >> Is it really? Wouldn't caster for a car correspond to head tube
> >> angle for a bike?

>
> > This is something I've never been 100% clear about.

>
> > People talk about trail on bikes, not caster. AIUI trail is the
> > offset from the projection of the head tube (which is the steering
> > pivot) onto the ground back to the contact point of the tyre.

>
> > Trail is a function of head tube angle, but also of fork
> > rake. Increase fork rake and you reduce trail for a given head tube
> > angle.

>
> OK, how about defining rake and its effect on trail instead of tossing
> out vague references. Keep in mind the definition given in English:
>
> http://www.m-w.com/dictionary/rake
>
> rake(3) being the one in question.


Here is a good reference for these matters.
<http://www.kreuzotter.de/deutsch/lenk.htm>
<http://www.kreuzotter.de/english/elenk.htm>

--
Michael Press
 
E

Ed Pirrero

Guest
On Feb 17, 10:15 am, [email protected] wrote:
> On Sat, 17 Feb 2007 02:16:37 -0600, Ben C <[email protected]> wrote:
> >On 2007-02-17, [email protected] <[email protected]> wrote:
> >> Ben C? writes:

>
> >>>>> Caster is called "trail" on bikes: it's the distance from the
> >>>>> projection of the steering pivot to the contact patch in the
> >>>>> forwards axis (not the sideways axis, which is scrub).

>
> >>>> Is it really? Wouldn't caster for a car correspond to head tube
> >>>> angle for a bike?

>
> >>> This is something I've never been 100% clear about.

>
> >>> People talk about trail on bikes, not caster. AIUI trail is the
> >>> offset from the projection of the head tube (which is the steering
> >>> pivot) onto the ground back to the contact point of the tyre.

>
> >>> Trail is a function of head tube angle, but also of fork
> >>> rake. Increase fork rake and you reduce trail for a given head tube
> >>> angle.

>
> >> OK, how about defining rake and its effect on trail instead of tossing
> >> out vague references. Keep in mind the definition given in English:

>
> >>http://www.m-w.com/dictionary/rake

>
> >> rake(3) being the one in question.

>
> >Someone previously posted this page, with a good diagram, which was what
> >I was thinking of:

>
> > http://www.kreuzotter.de/english/elenk.htm

>
> >and I'm glad to see I remembered the definitions of "trail" and "fork
> >rake" about right.

>
> [snip]
>
> Dear Ben,
>
> That diagram is worth a thousand words.
>
> As usual, the wheels don't care about our lexicographical arguments.
>
> As far as I can tell, anyone discussing rake and trail on RBT will be
> most helpful if he explains in passing which meanings he has in mind
> and move on to his real point about the effect of the geometry on
> handling.
>
> I cannot off-hand think of any common meaning that has been changed by
> appeals to dictionary sub-headings.


Jobst is funny that way - by using engineering jargon, he claims that
wheels "stand" on spokes.

Fine wordplay, but detrimental to anything but having a usenet
argument.

I find it hilariously ironic every time he complains about word use.

E.P.
 
M

Michael Press

Guest
In article
<[email protected]>
,
[email protected] wrote:

> On Feb 13, 11:19 pm, Michael Press <[email protected]> wrote:
> > In article
> > <[email protected]>,
> > Can we get the thread tree display from gg?

>
> Yes, you can get the thread-tree display from Google Groups for a link
> like this to an individual message:
>
> http://groups.google.com/group/rec.bicycles.tech/msg/af73416d9e457b72
>
> Near the top of an individual-message page will be a heading "Message
> from discussion whatever-the-thread-title-is"
>
> In this case, it's "Message from Custom fork- wheel ejection risk?"
>
> Click on the topic, and you'll go to the thread itself from the
> individual message:
>
> http://groups.google.com/group/rec....7b73c517e9/af73416d9e457b72?#af73416d9e457b72


The above url does indeed put up a tree view for me.
When I search for another thread, clicking on the
thread name does not bring up the tree on my
configuration. Instead I get a list of messages only.
<http://groups.google.com/group/sci.math/browse_thread/t
hread/7dd49d97f7649861/61f9a91a3c8e3343?#61f9a91a3c8e334
3>

_However_, when I manually substitute in this url:
s/browse_thread/browse_frm/
<http://groups.google.com/group/sci.math/browse_frm/thre
ad/7dd49d97f7649861/61f9a91a3c8e3343?#61f9a91a3c8e3343>
I get the tree view.

Behold, thou helmet warriors, what a dedicated sci.math
crank can accomplish. And this is not the only
concurrent thread.

--
Michael Press