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



T

Tim McNamara

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

> Tim McNamara wrote:
> > In article <[email protected]>,
> > jim beam <[email protected]> wrote:
> >
> >> [email protected] wrote:
> >>> On Feb 14, 3:48 am, Ben C <[email protected]> wrote:
> >>>> On 2007-02-14, [email protected] <[email protected]> wrote:
> >>>>
> >>>>> But third (and perhaps easiest to understand) is that the
> >>>>> specific thing jim beam warns about - front mounting of disk
> >>>>> brakes - has been employed on multi-hundred-pound motorcycles
> >>>>> for many decades. The direct tensile stresses that come from
> >>>>> such mounting are small, and very easily accommodated. If they
> >>>>> were not, NHTSA and CPSC would have told you about it in the
> >>>>> recall documents for those motorcycles.
> >>>> Noone's disputed that a front caliper is possible, but
> >>>> motorbikes are not bicycles.
> >>> True. They're much more massive, travel at much higher speeds,
> >>> and impose much higher forces on their caliper attachements.
> >>>
> >>>> All the relative pros and cons are different, which makes it a
> >>>> different optimization problem and we should not be surprised if
> >>>> it has a different solution. Lots of motorbikes do have rear
> >>>> calipers anyway.
> >>> Do you know of any motorcycle with a rear caliper and a quick
> >>> release front axle? I don't believe they exist. Every
> >>> motorcycle I've owned or seen had a through-axle. Thus, the
> >>> hazard imposed by a rear caliper was removed by other means.
> >> conversely, why aren't /all/ motorcycles front caliper? idiot.

> >
> > Who's the idiot, jim? Frank? Or you with your obstinate denial of
> > reality? If he's an idiot, you're a pathetic muppet.
> >
> > Through axles. No QRs. Ejection force not an issue.

>
> but you can already buy one. that's not a "design change"!!!


I can already buy one what? A motorcycle with a front-mounted disk
brake? Yup. Not actually interested, though. A bicycle with a front
mounted disk brake? Nope.

A bicycle with a rear mounted brake and a through axle? Yup. But
you're wrong- that *was* a design change since it came after the designs
we are talking about as flawed! Although it was made for other reasons-
through axles were made to provide a larger diameter axle to resist fork
twist and uneven travel.

> >>>>> So yes, there's a grain of metallurgical truth in what j.b.
> >>>>> says.
> >>>>> But the design proclamations he derives from it are nonsense.
> >>>>> He's making a mountain out of a molehill for reasons of his
> >>>>> own.
> >>>> The point is that wheel ejection is a molehill of similar
> >>>> proportions.
> >>> If you want to prove the front-mount-fatigue issue is of similar
> >>> importance to the bike wheel ejection issue, it should be easy
> >>> for you to do so. Just post here the tales of motorcycles losing
> >>> their front mount calipers due to fatigue. Carl has posted
> >>> several examples of candidate motorcycles to check. If you find
> >>> enough such tales, I'll believe the hazards are similar.
> >> post front wheel ejections where it's proven not to be user error!
> >> idiot.

> >
> > Post wheel ejections where it's proven to be user error! Muppet.

>
> oh, wait, circular argument based on supposition. surely not part of
> the research thesis is it?
>
> [p.s. don't let lack of ejection data get in the way of that one
> tim.]


Or the lack of tensile failures? LOL! C'mon, jim, you can do better.
Or can you?

> >>> My claim is that the fatigue hazard is entirely jim beam's
> >>> invention.
> >> i invented inferior fatigue properties for castings??? you don't
> >> even know what a casting is! idiot.
> >>
> >>> You have an opportunity to prove me wrong.
> >> no, you do that on your own. idiot.

> >
> > ROTFL! jim, do you get spittle all over your keyboard when you are
> > posting this drivel?

>
> eh? krygowski proves he knows nothing about castings and can't think
> through a simple stress sense scenario correctly? but pointing that
> out is drivel? get a grip on yourself man.


LOL! Here you are, ranting and raving and calling people "idiots" and
the like. And you're counseling others to get a grip? Priceless!
 
T

Tim McNamara

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

> Tim McNamara wrote:
> > In article <[email protected]>,
> > jim beam <[email protected]> wrote:
> >
> >> Tim McNamara wrote:
> >>> In article <[email protected]>,
> >>> jim beam <[email protected]> wrote:
> >>>
> >>>> dabac wrote:
> >>>>> jim beam Wrote:
> >>>>>> ....the real consideration of course is how great the collapsing
> >>>>>> force is in relation to capacity, not whether a collapsing force
> >>>>>> exists....
> >>>>> But you're completely ignoring the different orders of magnitude
> >>>>> of effort needed to address the different issues. Old school risk
> >>>>> reduction principles tended to foster a tunnel visioned approach
> >>>>> like that. Sure, wheel ejection is rare and avoidable through
> >>>>> known means, and there are other failures that are far more
> >>>>> common and equally if not more critical. But are there any who
> >>>>> are as easily corrected and with as little impact on the whole
> >>>>> concept of bike riding/bike owning as changing dropout angle
> >>>>> and/or caliper location(even if it only is to top mount and not
> >>>>> forward mount)?
> >>>>>
> >>>>> Of course one could, in the interest of safety, require that all
> >>>>> bike components should be redesigned with a bigger safety margin
> >>>>> and with redundancy on critical systems(2-circuit for hydraulic
> >>>>> brakes, double clamps on wire operated etc), but that would have
> >>>>> a major impact on just about every aspect on riding, servicing
> >>>>> and bike ownership. Assuming that fork molds gets changed
> >>>>> regularly anyhow changing dropout angle and caliper location OTOH
> >>>>> makes an admittedly small risk go away w/o any rider
> >>>>> consequences.
> >>>>>
> >>>>>
> >>>> to some extent, and i've said as much before.
> >>> Oh ********.
> >> you see tim, you huff and you puff, but you don't read the thread.
> >> other evidence suggests you don't understand much of it even if you
> >> do.

> >
> > You keep saying that in hopes of it becoming true, jim. Just wishful
> > thinking on your part.
> >
> >>>> but q.r. failure, the biggest issue in all this, will still lead
> >>>> to disaster, angled dropouts or not. all this chicken little b.s.
> >>>> based on irrational fears created by bad math, with the biggest
> >>>> adherents being non-engineers that can't grasp the most basic
> >>>> fundamentals, it beyond bizarre.
> >>> LOL. Perhaps somehow you keep overlooking the fact that two of the
> >>> biggest "adherents" *are* mechanical engineers, whereas the biggest
> >>> opponent *is not.*
> >> one doesn't know the difference between the fatigue characteristics
> >> of a material that strain ages and one that doesn't. the other
> >> doesn't know the sense of stress in bending. are they both useful to
> >> you in this appeal to an authority /you/ don't have?
> >>
> >>>> focus on the freakin' q.r., that's the safety issue, not the
> >>>> dropouts.
> >>> Duck, weave, circle and dodge.
> >> no tim, /you/ focus on the pertinent facts.

> >
> > I have all along, jim. You, on the other hand, have employed red
> > herring, straw men, obfuscation, etc.

>
> so why doesn't /your/ math work?


It does. It's very simple math, easy to do, and has been accepted by
the rest of the participants in the newsgroup. You've not posted any
corrections to it, either, so I can only conclude that you found no
errors in the numbers. Of course, the numbers I posted were specific to
my weight. As Jobst points out, the forces are proportional and scale
up or down easily.

Now, it may be that a 110 lb rider wouldn't be likely generate an
ejection force large enough to overcome the retention force provided by
the QR. A 220 lb rider might. A 300 lb rider, even more likely. Now,
that's just total force. It doesn't address the issue of cyclic
application of the ejection force and unscrewing the QR nut.
 
M

Mike Causer

Guest
On Thu, 15 Feb 2007 09:20:48 -0600, Ben C wrote:

> On 2007-02-15, Mike Causer <[email protected]> wrote:
>> On Thu, 15 Feb 2007 06:13:44 -0800, jim beam wrote:

> [...]
>>> brake tabs are "international". mounting bolts for this standard are
>>> perpendicular to the wheel, i.e. they're loaded in shear mode.

>>
>> Some were as you say, but many had the bolts in the plane of wheel which
>> would load them mostly in tension

>
> So were they also front-mounted?


No. Of course tightening a bolt puts it into tension, which must have a
greater value than anything that tries to unload it. Wikipedia tells the
world that one advantage of this sort of mount is that it allows some
lateral adjustment to align the caliper and rotor. If this is true, then
the bolt cannot be relied on to touch the sides of the hole it's in, and
the load is taken out through clamping friction. If that is insufficient
the bolt will bend.


Mike
 
E

Ed Pirrero

Guest
On Feb 15, 12:11 am, Ben C <[email protected]> wrote:
>
> Most cars I saw had them front mounted, but some were rear mounted.
>
> I saw a couple of Porsche 911s with cross-drilled discs. Grrr.


The OEM Porsche rotors are actually cast that way. With holes.

Much less prone to cracking than rotors which are cast solid and
drilled later.

My Audis have calipers mounted in front on the front wheels, and in
the rear on the rear wheels.

E.P.
 
T

Tim McNamara

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

> Tim McNamara wrote:
> > In article <[email protected]>,
> > jim beam <[email protected]> wrote:
> >
> >> Tim McNamara wrote:
> >>> In article <[email protected]>,
> >>> Ben C <[email protected]> wrote:
> >>>
> >>>> On 2007-02-14, [email protected] <[email protected]> wrote:
> >>>>> On Feb 14, 3:48 am, Ben C <[email protected]> wrote:
> >>>> [...]
> >>>>>> The point is that wheel ejection is a molehill of similar
> >>>>>> proportions.
> >>>>> If you want to prove the front-mount-fatigue issue is of
> >>>>> similar importance to the bike wheel ejection issue, it should
> >>>>> be easy for you to do so. Just post here the tales of
> >>>>> motorcycles losing their front mount calipers due to fatigue.
> >>>> If no such tales can be found that just proves that the
> >>>> motorcycle designers made sufficiently strong or
> >>>> fatigue-resistant caliper mounts to overcome the problem. I
> >>>> would expect the likes of Honda to get that right whatever the
> >>>> basic design. It doesn't tell us anything about the relative
> >>>> importances of fatigue and ejection.
> >>>>
> >>>>> My claim is that the fatigue hazard is entirely jim beam's
> >>>>> invention.
> >>>> Yes, I also give jim beam the credit for pointing out the
> >>>> fatigue hazard.
> >>> Pointing out the *presumed* fatigue hazard and then treating the
> >>> presumption as fact is more like it. There's no hard evidence to
> >>> support jim's claim that this is a hazard.
> >> look it up. tables for fatigue strength in castings. it's been
> >> posted here before.
> >>
> >>> And, of course he neglects
> >>> to mention that existing brake caliper bolts and their mounts are
> >>> not loaded only in compression.
> >> caliper bolts are mounted in shear. bolts are not cast.
> >>
> >>> This varies with the design of the mounts,
> >>> of course, as there are several in use.
> >> no, /all/ caliper bolts are in shear.
> >>
> >>> Hayes makes something like 13
> >>> different adapters for their brakes!
> >> and /all/ the caliper bolts are in shear.

> >
> > So then there's no problem with mounting the brake in front of the
> > fork leg, as all those motorcycle brakes prove.

>
> eh? it's raining wednesday, so i'll paint the house blue? do you
> even know what shear /is/???


Yup. Note, however that I was talking about the bolts *and* their
mounts. You decided to overlook what the post was actually about-
again- to serve yourself.

Unless you really wanted to claim that the mounts are loaded in shear?

> your cognitive myopia is downright scary.


LOL! In the land of the blind, the myopic man is king. LOL!
 
T

Tim McNamara

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

> On Wed, 14 Feb 2007 19:26:56 -0800, jim beam wrote:
>
> > no, /all/ caliper bolts are in shear.

>
> Except for the maybe 50% that aren't. Data obtained by examining the
> attachment of every disc brake on the stock of new bikes in Moon's Cycle
> Centre, Newmarket, England, yesterday afternoon.
>
> What I saw removed any doubts about front mounting, the weediness of some
> of the rear mounted setups has further convinced me that the load, and
> service life, would be very easily handled with a properly made front
> attachment.


Oh dear. Mike, Mike, MIke. Don't introduce actual observed facts into
the discussion. What fun is that? ;-)

Of course you're quite right. I too spent some time looking at these
brakes in bike shops a while back, which made the glaring errors in
jim's arguments all the more obvious.
 
B

Ben C

Guest
M

Mike Causer

Guest
On Thu, 15 Feb 2007 09:22:38 -0600, Tim McNamara wrote:

> Front *disk* calipers on bicycles are nonexistant.


I wouldn't be so sure. If you look at "Richards' 21st Century Bicycle
Book", published in 2000, the section on brakes includes a drawing of a
caliper mounted in front of the axle, albeit at the back of the bike. And
there was a reference recently to a current production bike with front
mounted front calipers.


>> On a minority of motorbikes.

>
> But in use none the less, which demonstrates the validity of the design.


As evidenced by the /majority/ of motorbikes in my garage. Two with front
calipers and one with rear calipers.



Mike
 
Ben C? writes:

>>>> [J.B.] I think this is not the place to learn about material
>>>> science.


>>> It's better than nothing.


>> Actually, it goes beyond that. This is also not the place to learn
>> about mechanical design to resist fatigue failure, and that's
>> really what we're discussing at the moment. j.b. appears to know
>> something about metallurgy, but he knows too little about
>> mechanical design. It's principles are by no means obvious.


> So explain them, or suggest a link.


As you say, you have an advanced education so finding the material
should be no problem.

>> You won't learn them here, and certainly not from jim beam.


> In my salad days I attended a top university myself, and learnt many
> things there. Almost to a man the tutors were as opinionated,
> egotistical, informative and full of **** as the best usenet cranks.
> The learning process consisted of filtering and thinking for
> yourself, no different to r.b.t. or life in general.


I'm sorry your schooling was at the mercy of such untalented teachers.
This was not my experience and I hold those professors memories in
high esteem. My respect for them grew as I became able to gauge their
skills against what I encountered in engineering, putting to use what
they taught. I cannot imagine "opinionated, egotistical, informative
and full of **** as the best usenet cranks" having any place in
education. When I hear such tales, it makes me feel I lead a charmed
life throughout my education beginning with kindergarten. A young
person should not be expected to separate true from false in
authoritative lectures in his learning years.

It's the same in life, when a person lies to you he cannot be believed
in anything he says that you don't already know. Somehow, this
concept eludes some people, especially public figures who depend on
people who do not understand the finality of lying.

Jobst Brandt
 
Ben C? writes:

>> But in use none the less, which demonstrates the validity of the
>> design.


> Noone ever disputed that the design could be made to work. The
> problem is one of optimization, and the details and hence the
> solution are different in the motorbike case.


Noon is when I eat lunch as no one would notice. The OED may have
something to say about that.

> As I've said, 2:30 caliper and front-facing dropouts are what I'm
> putting on the next disk-equipped MTB I design.


I had no idea you were designing bicycles. In that event, judging
from what you have written here, you should look over an experienced
frame builder's shoulders and understand what he's doing on before
building any bicycles.

Jobst Brandt
 
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]>,
> >
> >
> >
> >
> >
> > [email protected] wrote:
> > > On Mon, 12 Feb 2007 23:05:05 -0700, [email protected] wrote:

> >
> > > [snip]

> >
> > > >You may not like such questions, but they're the ones that any lawyer
> > > >or expert trying to reconstruct an accident would ask. Whatever Jobst
> > > >may think about the principles, here's his timely comment in another
> > > >current thread on plaintiffs and accident reconstruction:

> >
> > > >"I would like to have seen the bicycle [another bike, not Missy's]
> > > >right after the incident. It has been my experience that
> > > >reconstruction of what occurred is often easier than first
> > > >indications. That has been so, in every case in which I was called to
> > > >testify. That is to say, the event did not occur as plaintiff
> > > >described."

> >
> > > [snip]

> >
> > > Woe is me! I thought that I included the link to Jobst's post, but I
> > > didn't. Here it is:

> >
> > >http://groups.google.com/group/rec.bicycles.tech/msg/af73416d9e457b72

> >
> > Can we get the thread tree display from gg?
> >
> > --
> > Michael Press

>
> Dear Michael,
>
> 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"


Thanks.

> 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 advantages of an individual-message link is that it's shorter and
> goes directly to the messsage. Just using Google Groups search will
> only get you to the 10-post section of a thread that contains the
> target, not to the exact post.


On the occasions when I post a message link it is to a
page in fixed font with only the one message.

>
> So I find a post with the search function, but then use the shorter,
> direct link to the target (found under "more options" as "individual
> post"), but I forget that posters unfamiliar with Google Groups can
> easily get lost in the latest incarnation of what used to be an easier-
> to-navigate site.
>
> Whether you see a tree on the left of a full-thread display depends on
> what Google Group settings you choose under "more options" near the
> top, which lets you pick fixed or proportional text and whether to
> hide or display the "message list."
>
> In large threads, it can be tricky to find new posts. I usually sort
> the message-list/thread-tree by date and then grovel around at the
> bottom.


--
Michael Press
 
On Feb 15, 3:06 am, Ben C <[email protected]> wrote:
> On 2007-02-15, Tim McNamara <[email protected]> wrote:
> [...]
>
> > The ejection force is a demonstrable fact.

>
> Yes, but isn't the existence of a tensile fatigue cycle for a
> front-mounted caliper also a demonstrable fact?


Yes, it is. That's not your mistake in understanding.

Your mistake is to believe jim beam's assertion that cast aluminum can
never be designed to resist tensile fatigue. The obvious proof he is
wrong is that there are many motorcycles that do it, and do it
resisting much, much larger forces.

Less obvious is what I pointed out to you yesterday - that tensile
fatigue is common in _many_ bike components. And easy example is a
caliper brake arm, whether side pull, center pull, direct pull (V-
brake) or cantilever. Here's why:

Whenever something undergoes bending, tensile stress is generated.
See http://en.wikipedia.org/wiki/Bending for example, especially the
fourth diagram down. This tensile stress is not special to the
distributed load shown there, BTW. It happens essentially any time
something is bent. Furthermore, it's common that the tensile stress
generated by bending is greater than the tensile stresses encountered
in direct tension (as in the proposed front disk mounts). I can
explain that further, if necessary.

In any case, it's likely your brake arms undergo more tensile fatigue
than a front disk mount would see. It's also likely your brake arms
are cast. And they do just fine - just as motorcycle front disk
mounts do just fine.

> On a minority of motorbikes.


jim beam's idea is that one can never load a casting in tensile
fatigue. Logically, it requires only one counterexample to prove it
wrong.

- Frank Krygowski
 
B

Ben C

Guest
On 2007-02-15, [email protected] <[email protected]> wrote:
[...]
> I'm sorry your schooling was at the mercy of such untalented teachers.
> This was not my experience and I hold those professors memories in
> high esteem.


Don't get me wrong, I hold them in high esteem too (well most of them).

> My respect for them grew as I became able to gauge their skills
> against what I encountered in engineering, putting to use what they
> taught. I cannot imagine "opinionated, egotistical, informative and
> full of **** as the best usenet cranks" having any place in education.
> When I hear such tales, it makes me feel I lead a charmed life
> throughout my education beginning with kindergarten. A young person
> should not be expected to separate true from false in authoritative
> lectures in his learning years.


Depends how young. By university age I think it's reasonable to expect
some discernment from the student, which is why I think it's OK for
university teachers to give themselves a bit more latitude.

> It's the same in life, when a person lies to you he cannot be believed
> in anything he says that you don't already know. Somehow, this
> concept eludes some people, especially public figures who depend on
> people who do not understand the finality of lying.


Agree completely. But lying is a different kettle of fish from just
being a bit of a crank.

Actually public figures do get a lot of stick for lying. Wasn't this
pretty much what happened with Clinton-- noone was really too bothered
about his peccadilloes but the fact that he lied about them initially
gave his enemies a lot more to work with. This is a common scenario with
UK politicians-- they lie about an affair and have to resign, not
because of their "private life" which is respected, no matter how
sordid, but because they lied.

Lying about an affair is sort of OK. If I were going to make an
exception, it would be for that. Compared to Blair-style lying about WMD
it's nothing.
 
On 15 Feb 2007 11:30:09 -0800, [email protected] wrote:

>
>Your mistake is to believe jim beam's assertion that cast aluminum can
>never be designed to resist tensile fatigue. The obvious proof he is
>wrong is that there are many motorcycles that do it, and do it
>resisting much, much larger forces.
>
>Less obvious is what I pointed out to you yesterday - that tensile
>fatigue is common in _many_ bike components.


Well, no.

Tensile _stress_ is common.

Tensile _fatigue_ is not; and it's because components subject to such
stresses are (usually) designed to withstand them. Were they not,
well, we'd have failures.


> And easy example is a
>caliper brake arm, whether side pull, center pull, direct pull (V-
>brake) or cantilever. Here's why:
>
>Whenever something undergoes bending, tensile stress is generated.
>See http://en.wikipedia.org/wiki/Bending for example, especially the
>fourth diagram down. This tensile stress is not special to the
>distributed load shown there, BTW. It happens essentially any time
>something is bent. Furthermore, it's common that the tensile stress
>generated by bending is greater than the tensile stresses encountered
>in direct tension (as in the proposed front disk mounts). I can
>explain that further, if necessary.
>
>In any case, it's likely your brake arms undergo more tensile fatigue
>than a front disk mount would see. It's also likely your brake arms
>are cast. And they do just fine - just as motorcycle front disk
>mounts do just fine.
>
>> On a minority of motorbikes.

>
>jim beam's idea is that one can never load a casting in tensile
>fatigue. Logically, it requires only one counterexample to prove it
>wrong.


Don't try to teach a pig to sing; it wastes your time, and annoys the
pig.
 
Ben C? writes:

> [...]


>> question: in a situation where there is a known risk, but another
>> known benefit with a certain design, then what happens? example:
>> most modern cars have negative scrub radius for their steering.
>> it's "safe" because it tends to counteract the steering effect of a
>> front tire flat at speed thereby allowing an unskilled driver more
>> chance of retaining control and bringing the vehicle to a halt in a
>> controlled manner. but the danger is that it makes steering feel
>> light [and therefore "safe"] when braking /through/ corners,
>> thereby encouraging that unsafe habit.


> I used to drive a Mini which I believe had a zero scrub radius. I
> braked deep into corners (risk of a spin but the technique, once
> mastered, neutralized understeer and I felt allowed you to carry
> more speed through the corners). The car felt good doing that, I
> didn't notice the steering getting heavy or uncertain, although
> perhaps I was just used to it.


> I read in a book at the time that negative scrub radius made
> steering slightly vague around the centre position, but made
> motorway/freeway driving easier as constant steering correction was
> not required. I thought that was the purpose of it.


The purpose of the scrub radius is to take actual and elastic slack
out of steering linkage. Positive radius puts the linkage (ball
joints) in tension. The dimension being in the range of +- an inch.
It has nothing to do with handling except in FWD where it is generally
negative (offset to the inside) and comes into play when one wheel
loses traction, causing steering to have a bias to that side.
Positive radius does the same if braking on snow or ice for instance.

If you look at the jacked-up pickup truck/SUV syndrome with wheels
extended beyond the side of the vehicle, you see a guy who needs shock
absorbers on this drag-links. The scrub radius of these vehicles is
nearer to eight inches and puts a hell of a jolt on the steering wheel
when one wheels hits a sharp bump. Hey, but it looks cool!

> The Mini was designed in 1959 (before motorways), had very precise
> steering (low-geared, light, and the steering wheel was connected
> directly to the rack with no UJs in between), but did require more
> correction when cruising on motorways than the average 1980s
> shopping car.


That has more to do with trail than scrub radius, that has no
significant effect on road holding. That is why it is so small.

>> physics will tell you that braking through corners is a bad thing,
>> and positive scrub makes braking through feel heavy and uncertain,
>> thereby discouraging that kind of bad behavior. How might a legal
>> test be applied to that?


I think you are seeing ghosts, much like the tensile stress spook.

Jobst Brandt
 
B

Ben C

Guest
On 2007-02-15, [email protected] <[email protected]> wrote:
> On Feb 15, 3:06 am, Ben C <[email protected]> wrote:
>> On 2007-02-15, Tim McNamara <[email protected]> wrote:
>> [...]
>>
>> > The ejection force is a demonstrable fact.

>>
>> Yes, but isn't the existence of a tensile fatigue cycle for a
>> front-mounted caliper also a demonstrable fact?

>
> Yes, it is. That's not your mistake in understanding.
>
> Your mistake is to believe jim beam's assertion that cast aluminum can
> never be designed to resist tensile fatigue.


I don't think he asserted that. Or if he did I don't remember.

[...]
> Less obvious is what I pointed out to you yesterday - that tensile
> fatigue is common in _many_ bike components. And easy example is a
> caliper brake arm, whether side pull, center pull, direct pull (V-
> brake) or cantilever.


Yes indeed, although the forces are lower for a rim brake (by about a
factor of four).

[...]
> In any case, it's likely your brake arms undergo more tensile fatigue
> than a front disk mount would see. It's also likely your brake arms
> are cast. And they do just fine - just as motorcycle front disk
> mounts do just fine.
>
>> On a minority of motorbikes.

>
> jim beam's idea is that one can never load a casting in tensile
> fatigue. Logically, it requires only one counterexample to prove it
> wrong.


Again, I don't remember him making such an extravagant claim.
 
On Feb 15, 2:39 pm, [email protected] wrote:
> On 15 Feb 2007 11:30:09 -0800, [email protected] wrote:
>
>
>
> >Your mistake is to believe jim beam's assertion that cast aluminum can
> >never be designed to resist tensile fatigue. The obvious proof he is
> >wrong is that there are many motorcycles that do it, and do it
> >resisting much, much larger forces.

>
> >Less obvious is what I pointed out to you yesterday - that tensile
> >fatigue is common in _many_ bike components.

>
> Well, no.
>
> Tensile _stress_ is common.
>
> Tensile _fatigue_ is not; and it's because components subject to such
> stresses are (usually) designed to withstand them. Were they not,
> well, we'd have failures.


Correction accepted. What I meant was the stresses that would cause
tensile fatigue are common. Of course, it's easy for well-designed
parts to successfully resist those stresses.

- Frank Krygowski
 
B

Ben C

Guest
On 2007-02-15, [email protected] <[email protected]> wrote:
> On Feb 15, 5:05 am, Ben C <[email protected]> wrote:

[...]
> If you want to search for some of the theory used to design for
> fatigue, search on "failure theory" and perhaps Goodman's Criterion,
> Soderberg's Criterion, and Fracture Mechanics.


"Goodman's criterion for judging a particular performance to be of a
work W is that the performance comply with the score of W, i.e. an
accurate transcription into musical notation of what is actually played
must be identical with the score of work. W. Goodman's criterion derives
entirely and solely from the musically notatable characteristics of the
performance."

I suppose you must mean the _other_ "Goodman's criterion"...

Thanks for the tips, I'll have a look around. A very quick perusal
suggests that Soderberg's and Goodman's criterion are both about making
sure the use of a part is below its fatigue limit. AFAIK aluminium has
no fatigue limit-- it's always going to fatigue-fail eventually.

Anyway I shall read about it some more.

[...]
> I'm sorry your education was so miserable.


Not at all I enjoyed it a lot.