"Actually you are the first person to bring up this issue"

Jose Rizal writes:

Tim McNamara:

Ummm, oh yeah, that's *not* anecdotal evidence. That's objective
evidence, which the anecdotes (including video of a front wheel
ejection) serve to support.

You need to clarify that. Where is this video of a front wheel
ejection caused by the application of a disc brake? There has been
the video of a loose QR causing a wheel to come off the fork when
the rider tried to lift the handlebar while riding; you're not
referring to that?

No, James Annan has a video clip of a guy riding with some friends
across a parking lot; he hits the brake and the front wheel is
forcefully ejected and zooms away across the parking lot. He of
course stacks it headfirst into the pavement. Extremely dramatic and
demonstrative of the magnitude of the ejection force even at low
speeds.

Simon Brooke writes:

Merkins. They just don't do irony, do they? Something to do with
only having senses of humor, not of humour. There's a lot goes
missing with that second 'u'.

Mind you, of course, most of them wouldn't recognise humour of any
sort if it fell on them in a thunderstorm.

Hey! We resemble that remark! (Hmm, that may be a too-American
cultural reference).

Simon Brooke wrote:

Merkins. They just don't do irony, do they? Something to do with only
having senses of humor, not of humour. There's a lot goes missing with
that second 'u'.

Not sure why you feel the need to resort to silly euro-trash snobbery for a
cheap joke. Check back on my original post and you'll see it had a good
amount of irony and sarcasm, all meant to find humor in the gyrations of the
obsessed, sorry you were too wrapped up in your own prejudices to get it.
Perhaps it was too sophisticated for your worn, tired, uk-centric world view
(see, it works both ways...) Thankfully most of your countrymen aren't
quite provincial. I would have goofed on anyone who posted similar tripe,
regardless of nationality.

The good Mr Annan can claim his knee-jerk defensiveness was an attempt at
humor, but I don't buy it. Taken in the context of his other posts, I'm not
sure why one is supposed to view that through a humo(u)rous lense while
taking him seriously in all the others. Taken at face value, he's just
plain full of ****. He rejects the notion of contacting an agency who can
*do* something about the perceived problems, then retorts that he tried and
failed. Methinks he may want to recheck his facts or re-evalute the
veracity of his opinion. Looks like the laugh's on you.

Tom

In article ,
Tim McNamara wrote:

Jose Rizal writes:

Tim McNamara:

BenS writes:

Putting the caliper on the front of the fork would probably lead
to it ripping off it's mounting.

How do you figure? The forces on the mounting bosses on the fork
leg would be the same as they are with the current design.

BenS is probably referring to the post type mounts (Manitou), where
the axes of the mounting bolts are parallel to the plane of the
rotor. If a caliper with this type of mount is placed in front of
the fork, the bolts are going to take the caliper braking load in
tension (not a good idea in general), whereas if the caliper is
behind the fork, it is the mounting posts that take up the load (and
in compression), the bolts serving merely to fix the caliper in
place.

Hmm. Thanks for clarifying this.

Is it really so bad for the bolts to be in tension? As I understand this
stuff, the way a bolt works is that when you tighten it properly, you're
effectively loading it with a whole bunch of tension.

http://www.unified-eng.com/scitech/bolt/clamping.html

Now, it's even easier to hold together if you can get the parts to be in
compression, but it shouldn't be necessary for the forces a disc brake
is likely to exert on the bolts. A typical Grade 5 bolt has a tensile
strength of 120,000 psi. Now, the bolt cross sections are only a
fraction of a square inch, (my back-of-the envelope calculation is .02
sq. in.) but that still amounts to about 2000 pounds of tensile
strength, per bolt.

The spec in the quoted article above suggests taking the bolt to about
75% of yield in a typical torquing, so that means you've added maybe
1500 pounds of preload, and that means in order to rip two
well-tightened bolts off of the front of a brake caliper, you'd have to
generate some pretty scary braking forces.

Of course all these don't matter to IS mounts, where the mounting
bolts lie perpendicular to the rotor plane.

Which make sense.

Well, it doesn't matter, but now you're loading the bolts in shear,
something against which they are not well preloaded and not designed to
resist. Look around you in the world: how many examples do you see of
shear-loaded fasteners? The only examples besides disc brake mounts that
I can think of are riveted sheet metal in stressed-skin systems (as on
airplane skins), and they use a _lot_ of rivets. Wheel mounts do a
similar thing, but use conical nuts to prevent true shear loading.
Pedals are a bad example of how not to do this; read Jobst's entry in
the rb FAQ for why not.

Motorcycles are rapidly moving away from IS-style mounts to post mounts,
which they call "radial" mounting, as in radial relative to the wheel.
The claimed advantages are strength and weight.

--
Ryan Cousineau, http://www.sfu.ca/~rcousine/wiredcola/
President, Fabrizio Mazzoleni Fan Club

James Annan wrote:
tcmedara wrote:

LOL. While I think you are an obsessed quasi-religious zealot,
that's not why I'm going to goof on you.....

Dumabass, Frobnitz was *supporting you* !

Yeah, I realised that. I guess humo(u)r doesn't travel well.

Perhaps you should give it up for something you're better at...


He was suggesting that rather
than spam up a bunch of newsgroups where people are probably smart
enough to tighten their QR, you should direct your efforts at the
appropriate regulatory agencies and actually try to do something to
fix the "problem".

Actually, although you probably mean well, both you and Frobnitz don't
seem to realise that I _did_ contact the "appropriate regulatory
authorities" last year. They (or, to be precise, the CPSC) said they
needed specific complaints of individual problems, rather than a
general warning of a theoretical design problem.

I don't mean well at all. I responded 'cause I find humor in pointing out
logical inconsistency. I didn't "realise" you'd contact anyone because you
rejected the notion as not worthwhile. I'm pretty intelligent, but not
clairvoyent. I could have realized it had you bothered to mention it.
Maybe you should listen to the CPSC and ask why riders *haven't* contacted
said agency? Maybe your perception of the problem doesn't translate into
reality.

Of course, when I suggested that some of those riders who had
described their incidents might care to contact the CPSC, I was
roundly criticised for "scaremongering", and as far as I know, not a
single rider bothered. Many of those who understood the problem or
had even seen it for themselves had the touchingly naive belief that
the manufacturers would fix the problem all on their own and it would
be overkill to actually pressure them into doing so. Of course, what
they didn't realise is that the manufacturers have a strong financial
incentive to keep the current designs, since when Joe Bloggs upgrades
to disks and finds his QR fork is not up to the job, he then
generally goes out and buys a bolt-through fork. It's easy enough to
see who wins out of this.

Conspiricy theory itself is always touchingly naive. If the manufacturers
change the design then you're vindicated and if they don't, then they're
involved in the cover-up --and you're vindicated again! Is that how it
works in the land of absolute truth? (...and that's meant to be ironic
humor for your challenged countryman, Simon). Don't understand? Perhaps
you'd better start he http://tinyurl.com/282zg


Roll on one year, and entirely predictably, the manufacturers are
still pretending the problem doesn't exist. They must be laughing all
the way to the bank.

.....Or secure in the knowledge that the problem doesn't actually exist.

As for J DeMarco at the CPSC, well he commissioned Mark LaPlant of
Cannondale to report on the issue, and surprisingly enough the turkey
didn't vote for Christmas. In fact he produced a bull**** whitewash
which he refuses to publish. But since all the manufacturers can
(apparently truthfully) claim that no rider has ever reported any
incident, there really is little more that the CPSC can (or probably
should) do.

Again, not the "truth" you espouse so therefore it's a "whitewash". Next
you're going to tell us the CIA is behind it all right? Ya know, if you
could document actual circumstances (rather than internet anecdotes and
gossip), than you could prove the point to the apparently intransigent CPSC.

Your rejection of that course of action suggests that you're more
interested in pursuing your own personal crusade rather than
actually solving a problem -- percieved or otherwise.

Rather than thank him for the suggestion or offer a counterpoint to
why it's not a viable option,

I hope you will now agree that I have offered a counterpoint as to why
it is not a viable option, and I'm sorry for not giving sufficient
explanation earlier. The simple fact is that while MTBers refuse to do
more than grumble on bulletin boards, there is no real complaint to
raise with anyone. I realised several months ago that there was really
nothing more for me to do, but people still keep on emailing me with
their stories, and I thought this latest one was sufficiently
interesting to be worth sharing. Maybe next year there will be
another. Don't hold your breath.

So we can look forward to a year's peace on the matter? Or does this mean
that anytime someone reports a UFO, ....er disk/QR malfunction we'll be
treated to another lecture on the apathy of the injured and the evil intent
of the bike industry? You complain of apathy on the part of MTBers who do
nothing but "grumble on bulletin boards", and then resign yourself to do the
same. Again -- is this more of the internal debate going between the
personalities who live in your head? Maybe you nailed it by suggesting
"there is no complaint to raise with anyone."

Just a thought

Tom

Ryan Cousineau:

Is it really so bad for the bolts to be in tension? As I understand this
stuff, the way a bolt works is that when you tighten it properly, you're
effectively loading it with a whole bunch of tension.

http://www.unified-eng.com/scitech/bolt/clamping.html

This is right, but torquing a bolt for holding parts together is
different from getting that bolt's threads to take a load above its
torque specification because it's not always just the bolt you worry
about, but what it's threaded into. Depending on length of engaged
thread, it's possible to have the threaded contact area to be smaller
than the bolt's radial cross-sectional area which means that even though
the bolt itself can survive the tensile load, the threads on either the
bolt or the material it's screwed into might not. See below.

Now, it's even easier to hold together if you can get the parts to be in
compression, but it shouldn't be necessary for the forces a disc brake
is likely to exert on the bolts. A typical Grade 5 bolt has a tensile
strength of 120,000 psi. Now, the bolt cross sections are only a
fraction of a square inch, (my back-of-the envelope calculation is .02
sq. in.) but that still amounts to about 2000 pounds of tensile
strength, per bolt.

The spec in the quoted article above suggests taking the bolt to about
75% of yield in a typical torquing, so that means you've added maybe
1500 pounds of preload, and that means in order to rip two
well-tightened bolts off of the front of a brake caliper, you'd have to
generate some pretty scary braking forces.

You need to look at the mounting post threads strength, not the bolts
themselves. The posts are made of aluminium and don't have the
characteristics you outlined above. The post will strip first before
the bolt . Using _threads_ on bolts to take up loads is always bad
design; using the bolt body to take up tensile loads is _always_ better.

Of course all these don't matter to IS mounts, where the mounting
bolts lie perpendicular to the rotor plane.

Which make sense.

Well, it doesn't matter, but now you're loading the bolts in shear,
something against which they are not well preloaded and not designed to
resist. Look around you in the world: how many examples do you see of
shear-loaded fasteners? The only examples besides disc brake mounts that
I can think of are riveted sheet metal in stressed-skin systems (as on
airplane skins), and they use a _lot_ of rivets. Wheel mounts do a
similar thing, but use conical nuts to prevent true shear loading.

Go into a construction site and be awash with examples. Look at the
steel girders, beams and other metal support structures that are bolted
together. Look at the bolted structures on bridges; the parts that put
bolts in pure tensile loading don't rely on the _threads_ to take up the
load, but on the strength of the bolts themselves.

Bicycle wheel axles are bolts in shear. Imagine a design that relies on
your QR skewer directly taking up your weight in tensile loading.

Pedals are a bad example of how not to do this; read Jobst's entry in
the rb FAQ for why not.

Motorcycles are rapidly moving away from IS-style mounts to post mounts,
which they call "radial" mounting, as in radial relative to the wheel.
The claimed advantages are strength and weight.

Maybe, but you can bet money that the "new" radial designs will not be
relying on bolts' threads taking up the loads in tension.

Tim McNamara:

Jose Rizal writes:

Tim McNamara:

Ummm, oh yeah, that's *not* anecdotal evidence. That's objective
evidence, which the anecdotes (including video of a front wheel
ejection) serve to support.

You need to clarify that. Where is this video of a front wheel
ejection caused by the application of a disc brake? There has been
the video of a loose QR causing a wheel to come off the fork when
the rider tried to lift the handlebar while riding; you're not
referring to that?

No, James Annan has a video clip of a guy riding with some friends
across a parking lot; he hits the brake and the front wheel is
forcefully ejected and zooms away across the parking lot. He of
course stacks it headfirst into the pavement. Extremely dramatic and
demonstrative of the magnitude of the ejection force even at low
speeds.

That video has been clarified by Annan in http://tinyurl.com/2d3p3

********
"I should point out that this was not a wheel pulled out through
application of a disk brake. It was due to a stripped thread in the QR,
possibly due to overtightening, and then the wheel fell out. It's an
illustration of why 'just do up the QR tighter' isn't an answer, and
neither is 'so what, MTBers fall off all the time'. Even at low speed on
a level surface it isn't an everyday sort of fall.

http://www.ne.jp/asahi/julesandjames/home/ride.mpg"
********

It's not what you think it is.

Tim McNamara writes:

I keep hearing about this issue with greater frequency, but I've
been running discs for a few years now and it's only popped out
once in that time. It was my fault on that occasion, I realized
afterwards that I hadn't properly tightend the QR.

What means "properly tightened"?

See, that's the point. The brake should be designed so that it
*can't* force the wheel out of the dropouts, even if the QR is left
completely loose. It's a design flaw, an epic design flaw that will
cost some manufacturer a *lot* of money in court some day. No other
current brake design that I'm aware of puts an ejection force into
the wheel in normal operation, but front disk brakes do.

Hold it! Even though this has been discussed at great length here in
wreck.bike, it appears to me that most of the respondents did not
understand that a disc caliper behind the fork causes a wheel
disengaging force, and that repeated braking WILL loosen a QR.
Therefore, with the majority of contributors resting in the "James
Annan is all wrong" boat what you just posted gets us back to the
start, a few hundred responses ago.

Brake forces and their reactions are apparently to complex to be
discussed among bicyclists who believe anything bought in a bicycle
shop is safely designed.

http://www.ne.jp/asahi/julesandjames...quick_release/

Jobst Brandt

anonymous snipes:

The bottom line here is not whether or not this issue is truthful,
but how and why it happens. I for one would like to know what the
circumstances are in each case that may trigger it.

So the question is this: in each case where the problem occured,
what were the conditions? was it human error, or part failure?

How about doing a test that takes about 30 seconds. Open the QR on a
disc brake equipped front wheel. Push the bicycle forward and notice
what the axle does.

Just so it is clear what occurs. The fork dropout rises from the axle
and is retained only by the retention lips. the motion involved will
cause a properly closed QR to loosen on repeated hard braking because
there is ever so little motion with each brake application. If the QR
is extremely tight, it can prevent this over a longer time but in the
long run, if the wheel is not removed for one reason or another and
reinstalled again made extra tight, it will loosen.

The point is that the wheel should not have disengaging forces while
braking. These would not occur if the caliper were mounted in front
of the fork.

Jobst Brandt

wrote:
Tim McNamara writes:


Brake forces and their reactions are apparently to complex to be
discussed among bicyclists who believe anything bought in a bicycle
shop is safely designed.

http://www.ne.jp/asahi/julesandjames...quick_release/


I don't think that at all, but I'm also not going to condemn a product or
indict an entire industry as a result of some line drawings and vector
calculations. Apart from some internet anecdotes and urban legend, I've yet
to see anything remotely resembling evidence of a threat to the public
safety. To illustrate, my lovely wife subscribes to the CPSC mailing list.
We receive an email nearly ever day listing between 1 and 5 different
product recalls. These recalls typically describe what is often potential
flaws and possible dangers -- many of which are damn near laughable but
still result in a recall:

Here's a few examples:
http://tinyurl.com/223qd
http://tinyurl.com/2n2sn

Surf the site and ask yourself if the CPSC is going to overlook the disk
brake risk when bicycle product recalls are issued for injuries no more
severe than a broken finger. http://tinyurl.com/3yxvb

I'm the last person to believe the government (US or anywhere else) ought to
be the ever protective nanny, and I'm not suggesting that if the CPSC isn't
interested than there's no problem. I'm merely illustrating that the idea
of a huge conspiricy to cover up the problems, and a tremendous lack of hard
evidence suggests the "problem" exists in the realm of the theoretical only.

Hell, I don't even ride with disks and I think the whole debate is a crock.

Tom