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

Mike Causer 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.


Mike

unless you're looking at old stock or something custom, brake tabs are
"international". mounting bolts for this standard are perpendicular to
the wheel, i.e. they're loaded in shear mode. even old stock mountings
with the other type of mounting [whatever it's called] have bolts in
compression mode, not tension, the undesirable mode.

Ben C wrote:
On 2007-02-15, jim beam wrote:
[...]
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,

negative scrub tends to be small - that's what makes it vague. that and
the fact that it's usually married to macpherson...

but made motorway/freeway
driving easier as constant steering correction was not required. I
thought that was the purpose of it.

it's about flats. in positive scrub, a flat will drag you off to the
side of the flat, possibly into oncoming traffic if you're not alert.
negative, and if you think about it this makes sense, has the drag force
in the steering acting counter to the drag force on that corner of the car.


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.

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?

On Thu, 15 Feb 2007 06:13:44 -0800, jim beam wrote:

Mike Causer 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.

unless you're looking at old stock or something custom,

Many of them said "Shimano" on the side, and they were being sold as
"2007" stock. Bike makes were Raleigh, Marin and a couple of others.


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, and presumably are intended to take the
braking load out through friction between the clamped faces. I believe
this is called "post mount" by the fork and brake manufacturers.


Mike

In article ,
jim beam wrote:

Tim McNamara wrote:
In article ,
jim beam wrote:

Tim McNamara wrote:
In article ,
Ben C wrote:

On 2007-02-14, wrote:
On Feb 14, 3:48 am, Ben C 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.
whoops, missed that peachy bit! now let me get this straight - a
presumed hazard cannot be taken as fact? is that correct? a
presumed hazard like disk ejection? i just want to be sure
because materials literature is full of data on casting fatigue
behavior - that's known to most people as "hard evidence".

The ejection force is a demonstrable fact. You've stipulated to
that already, unless you are (once again) changing your position.

the presumption is that it exceeds retention force!!! jeepers.

And it's been shown to you over and over again that the ejection force
can exceed the retention force.

The presumed catastrophic failures that you are treating as fact
has not been demonstrated.

but there's extensive lit on it! what more do you want?

There's extensive literature on reaction forces, there's extensive
literature on threaded fasteners unscrewing, etc. Now what? Is it time
for the various participant to start throwing citations at each others?

Indeed, since perfectly workable forks with the calipers in front
exist, your claim seems rather specious.

on [a very small minority of] motorcycles with somewhat different
design.

So, as you now stipulate, it can be done successfully.

cheap lightweight castings are not the place for tension, for reasons
detailed in material lit at great length. and the angled fork design
is useless against a failed q.r!

I'm sure the fork industry- and their customers- would appreciate your
characterization of their products as "cheap lightweight castings."
It's lovely how in one breath you staunchly defend them and in the next
impugn them. Hilarious!

If you're so worried about failed QRs, then go to a through-axle design.
Not going to be very popular with the average buyer, though. That would
solve the problem and allow you to retain your precious
caliper-behind-the-fork design that you love so well and defend so
passionately, blindly ignoring the major design flaw.

How often do QR failures happen, do you think? And why? I have seen
one broken QR in 40 years of riding bikes. Close examination suggested
that the skewer had been slightly bent, although whether prior to the
fracture or as a result of it, I don't know.

Mountain bike suspension forks- except the Headshock design- subject QRs
to unusual forces for which they were not designed. The forklegs can
have a degree of independent movement which the skewer must resist.
Then you add the ejection force from a disk brake, and you have added a
lot of forces on the QR which were not envisioned when Tullio Campagnolo
came up with the design. All the more reason to eliminate the
unnecessary ejection force.

On 2007-02-15, Mike Causer 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?

and presumably are intended to take the braking load out through
friction between the clamped faces. I believe this is called "post
mount" by the fork and brake manufacturers.

In article ,
Ben C wrote:

On 2007-02-15, Tim McNamara 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?

jim is worst-case-scenario-ing the design. He's also ignoring tension
in some of the existing rear-mount designs.

You've stipulated to that already, unless you are (once again)
changing your position. The presumed catastrophic failures that
you are treating as fact has not been demonstrated.

There's precious little evidence of catastrophic failures due to
_either_ demonstrable fact (ejection force or tensile fatigue).

There is some for the former, none yet for the latter since those forks
don't exist for bicycles.

Back to your "absence of evidence != evidence of absence" idea-- we
would expect to see frequent ejections, if they are a problem, since
rear calipers are out there in the wild in their tens of thousands.

And I say wonderful! I am glad that there has been no rash of these
failures. But I am concerned that there have been partial failures-
loosening of the QR- that would confirm the analysis and which we simply
don;t hear about because the rider assumes user error as the culprit.
After all, we have all had the lore drilled into us that QRs only fail
because of user error. But that was before suspension forks and disk
brakes put unforeseen stresses on QRs.

Front calipers on bicycles are rare.

Front *disk* calipers on bicycles are nonexistant.

There is more evidence that ejection is not a problem in practice
than there is that tensile fatigue is not a problem.

Unless you are hiding evidence of tensile fatigue problems in disk rbake
bicycle forks, that issue is simply untested. jim may be right, he may
be wrong. Until prototypes are made tested and examined we don't know.
There is no proposed mount design to consider.

Indeed, since perfectly workable forks with the calipers in front
exist.

On a minority of motorbikes.

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

In article ,
jim beam wrote:

Tim McNamara wrote:
In article ,
jim beam wrote:

wrote:
On Feb 14, 3:48 am, Ben C wrote:
On 2007-02-14, 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!

In article ,
jim beam wrote:

Tim McNamara wrote:
In article ,
jim beam wrote:

Tim McNamara wrote:
In article ,
jim beam wrote:

Tim McNamara wrote: snip
FWIW my logic goes:

A. A disk brake can cause an ejection force on the front
wheel. B. There is no need for an ejection force, as forks can
easily be designed to eliminate it. C. Forks should be
redesigned to eliminate the ejection force.

The background assumption, of course, is that wheel ejection is
a bad thing and is to be avoided.
the logical flaw is amazing. illustration:

1. use of a bridge causes a collapsing force on it. 2. there is
no need for a collapsing force. 3. bridges should not be used.
Yes, the logical flaw is amazing. However, it's the glaring hole
in your classic red herring logic (or if you prefer, ignoratio
elenchi) that amazes.
that's just ****. focus on the facts.

I am, jim. And the fact is that you are a moron. You've made it
clearer and clearer and clearer with every post.

It is a false analogy. A bridge cannot be used without a
collapsing force
tim, this is why you have no dog in the hunt - you don't
understand the basics. /all/ bridges are used with collapsing
force, just one of lesser magnitude than the force that succeeds.

In a word, "duh." You are so engaged in proving me wrong that you
don't even bother to read and understand what I write.

"it is a false analogy"???

Yes, jim. Perhaps you should have taken that class in logic. It'd help
right about now.

and there is no way to design it otherwise,
that's the whole point big guy. but you /can/ determine the
bounds, and if you operate within bounds, you can call that
"safe". see above for magnitude.

but a disk brake can be easily designed to be used without an
ejection force.
can that same design withstand a defective q.r? if not, it has no
value.

Yes, it can. That's the point of the redesign. Are you even
paying attention?

eh? you'd ride with a defective q.r.? that's bull.

Knowingly? Of course not. I didn't say I would, so we're back to your
straw man tactics. The point is that the fork should not eject the
wheel if the QR fails. Hence there should be no ejection force.

Surely you can't really be this dense. You'd never hold down a job!

repeated failure to recognize that fundamental point is a truly
extraordinary mental block.
ROTFL! Pot, kettle, black.
you don't get it tim.

You keep saying that. But you're wrong.

see above.

Sad and pathetic to witness, jim.

In article ,
jim beam wrote:

Tim McNamara wrote:
In article ,
jim beam wrote:

Tim McNamara wrote:
In article ,
jim beam 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 bull****.
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.

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

On 2007-02-15, Mike Causer 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