Re: Marzocchi comes clean

CKAGMD@webtv.net

Tony Raven wrote:
> On a recent ride with a group of about 15 fairly serious riders

What, were they frowning most of the time instead of highly serious
riders who frown constantly?

Get serious.

JD

James Annan

Pete Jones wrote:


>
> http://www.bikemagic.com/forum/foru.../last/1/V/6/SP/
>
> Just stirring the pot, you understand...
>

Hope he's looking forward to some cool scars.

This one was good too:

http://www.singletrackworld.com/for...50407&t=1450407

Took the clueless muppet a week to work out what had happened.

Neither of these people was the one who got that email from Marzocchi,
BTW (he also crashed in late November).

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

Tony Raven

James Annan wrote:
>
> This one was good too:
>
> http://www.singletrackworld.com/for...50407&t=1450407
>
> Took the clueless muppet a week to work out what had happened.
>

Is that the right link - its an unresolved thread about someone
discovered wandering around dazed and hurt at work not knowing how he
got there.

Tony

Tony Raven

James Annan wrote:
> Pete Jones wrote:
>
>
>>
>> http://www.bikemagic.com/forum/foru.../last/1/V/6/SP/
>>
>>
>> Just stirring the pot, you understand...
>>
>
> Hope he's looking forward to some cool scars.
>

Does he indicate anywhere he was braking at the time? Says he "was on
last (very easy, straight, fire trail) 25mph downhill home. One minute
there was a front wheel, then there wasn't." He doesn't mention
touching the brakes at all immediately prior to losing the wheel and it
sounds the sort of situation where you don't brake and see how fast you
can go. Do you know otherwise?

Nice example though of a helmet once again failing by brittle fracture
and not doing its job.

Tony

Westie

JLB wrote:
> Westie wrote:
>
>> Alien Rider wrote:
<snip>
>>> http://makeashorterlink.com/?T538360A4
>> The math is fine, but despite a massive page of photos and
>> calculations it still says on the page that THE QR SKEWER MUST HAVE
>> COME LOOSE. Regardless of the braking system that I used, I would be
>> packing myself if I discovered that the skewer had come loose on a
>> steep downhill.
>>
>> I don't see that it's particularly the fault of the disc brakes.
>
>
> This seems an odd statement if you actually accept the calculations
> given on the web page. <snip> It also points out that the accepted
> standard for QR systems leaves little or no margin with forces of this
> magnitude.

Yes, the forces applied are enormous and excessive, but if I've read it
correctly these calculations talk about the force required to break or
tear the skewer from the dropouts. In practice, it would seem that the
QR skewers are NOT breaking or being torn from the dropouts. They are
coming open or loose first, and THEN the wheel is ejected. At least
that anectdotal account that you refer to indicates that the QR came
loose. Why is that? What is going on here to loosen the QR if that's
what happens?

> Finally, if it is not connected with disc brakes, why is it riders of
> bikes with disc brakes that are reporting this problem?

Good point. Trouble is that much of it is anectdotal evidence that
isn't easily replicated under controlled conditions to eliminate bias.
Maybe it has been happening with rim brakes? Maybe it is incorrectly
adjusted QR locks? Many features on modern mountain bikes are
relatively new. There are larger numbers of people riding modern
mountainbikes than ever before. I'm just not convinced that this
problem is entirely unrelated to incorrectly adjusted equipment for the
most part. I'm not sure how big this problem is in real life.


>> Granted, it seems that they make it more likely that the wheel is
>> ejected when the QR skewer does come loose, but I wouldn't want to
>> take any chances with a loose skewer and rim brakes either.
>
>
> I don't think anyone is suggesting you should.
>
>>
>> The debate about ejection forces from discs is not the issue. What
>> you should be calculating is the rotational force on QR skewers that
>> disc brakes or rim brakes exert to cause the QR to loosen. That's
>> where the fault lies. Once that QR is loose the end result will
>> eventually be the same regardless of whether you are using disc
>> brakes, rim brakes or sticking your feet down like Fred Flintstone...
>>
>> It seems to me that you are blaming disc brakes for a problem that QR
>> skewers have. I'd be interested in finding out how a properly
>> adjusted QR skewer comes loose even under massive amounts of vibration
>> too.
>
>
> There is at least one carefully written post in this thread from someone
> who was clearly very conscious of the potential for this problem. It
> describes a skewer that was correctly adjusted at the top of a hill
> being loose before the bottom of the hill. QR skewers are made to
> standards that do not take adequate account of the forces involved in
> common disc brake designs. So, its the combination of the two things: QR
> skewers that are designed for, and perfectly adequate with, rim brakes;
> and disc brakes that produce forces that dramatically increase the
> possibility that the skewer fails to retain the wheel.

So why is that? The calculations went to the trouble of demonstrating
forces that are capable of ripping a correctly adjusted QR from the
drop-out or breaking it. But that doesn't seem to be what is happening
in reality. WHY did the QR become loose in this example and NOT be
ripped out? Maybe it's not the fault of the disc brakes, but a fault of
QR in general that is just becoming widely acknowledged? Maybe QRs have
been coming loose for years? Now that brakes have been developed that
will eject those loose skewers it's time to examine options to secure
the skewers and prevent them from coming loose in the first place.

Regardless of the fault it does sound like it is time to take another
look at the design of systems used to hold the front wheel on.
--
Westie

JLB

Westie wrote:
> JLB wrote:
[snip]
>> This seems an odd statement if you actually accept the calculations
>> given on the web page. <snip> It also points out that the accepted
>> standard for QR systems leaves little or no margin with forces of this
>> magnitude.
>
>
> Yes, the forces applied are enormous and excessive, but if I've read it
> correctly these calculations talk about the force required to break or
> tear the skewer from the dropouts.
The calculations describe the forces in various directions, and resolve
them to calculate the force acting directly in line with the dropout.
The page compares that force with the standard. The standard is a
minimum acceptable for a QR skewer. It says that in practice reasonably
(not necessarily perfectly) adjusted skewers easily exceed the minimum.
However, a skewer at the minimum leaves next to no margin.

In practice, it would seem that the
> QR skewers are NOT breaking or being torn from the dropouts. They are
> coming open or loose first, and THEN the wheel is ejected. At least
> that anectdotal account that you refer to indicates that the QR came
> loose. Why is that? What is going on here to loosen the QR if that's
> what happens?

Brakes go on, brakes go off; the wheel grips the ground, the wheel
skids, the wheel lifts off. The most difficult thing to model here is
what happens when forces of this magnitude rapidly build up and then
disappear. The forces are fluctuating wildly. What does this do to the
adjustment on the skewer? It's not clear. All we know is the skewer is
not made for that sort of battering; the forces act in an undesirable
direction; and riders are reporting their skewers coming loose or even
their wheels falling out.
>
>> Finally, if it is not connected with disc brakes, why is it riders of
>> bikes with disc brakes that are reporting this problem?
>
>
> Good point. Trouble is that much of it is anectdotal evidence that
> isn't easily replicated under controlled conditions to eliminate bias.
> Maybe it has been happening with rim brakes? Maybe it is incorrectly
> adjusted QR locks? Many features on modern mountain bikes are
> relatively new. There are larger numbers of people riding modern
> mountainbikes than ever before. I'm just not convinced that this
> problem is entirely unrelated to incorrectly adjusted equipment for the
> most part. I'm not sure how big this problem is in real life.
>
I agree with you that the data is inconclusive. It is also obvious that
whatever the actual problem here, people do ride around on bikes with QR
skewers and disc brakes without disaster. In so far as there is a
problem, it is still unusual. But I would not want it to happen even
once when I'm riding. Among other things, it's one of those problems
that will only happen when you least want it, not when you're riding
nice and gentle along flat smooth ground.
[snip]
>> There is at least one carefully written post in this thread from
>> someone who was clearly very conscious of the potential for this
>> problem. It describes a skewer that was correctly adjusted at the top
>> of a hill being loose before the bottom of the hill. QR skewers are
>> made to standards that do not take adequate account of the forces
>> involved in common disc brake designs. So, its the combination of the
>> two things: QR skewers that are designed for, and perfectly adequate
>> with, rim brakes; and disc brakes that produce forces that
>> dramatically increase the possibility that the skewer fails to retain
>> the wheel.
>
>
> So why is that? The calculations went to the trouble of demonstrating
> forces that are capable of ripping a correctly adjusted QR from the
> drop-out or breaking it. But that doesn't seem to be what is happening
> in reality. WHY did the QR become loose in this example and NOT be
> ripped out? Maybe it's not the fault of the disc brakes, but a fault of
> QR in general that is just becoming widely acknowledged?

There is a substantial demonstrable difference in the forces from a disc
brake, as opposed to a rim brake, that make it credible as part of the
problem. My suggestion (I have no further evidence to back this up) to
explain the observations is above. The fact that the standard for
skewers is a minimum and the forces produced by the disc brake are
around that minimum does, however, explain why the skewers do not simply
break and are not simply instantly ripped out of the forks. The forces
are still a considerable way short of breaking a skewer that is in good
condition. Because a typical skewer can stand forces well in excess of
the minimum the disc brake cannot not rip out the wheel until the skewer
has been loosened to some extent. However, threaded fasteners loosening
under violent vibration is not unknown.

Maybe QRs have
> been coming loose for years? Now that brakes have been developed that
> will eject those loose skewers it's time to examine options to secure
> the skewers and prevent them from coming loose in the first place.
>
> Regardless of the fault it does sound like it is time to take another
> look at the design of systems used to hold the front wheel on.

Agreed.


--
Joe * If I cannot be free I'll be cheap

jim beam

JLB wrote:
> Westie wrote:
>
>> JLB wrote:
>
> [snip]
>
>>> This seems an odd statement if you actually accept the calculations
>>> given on the web page. <snip> It also points out that the accepted
>>> standard for QR systems leaves little or no margin with forces of
>>> this magnitude.
>>
>>
>>
>> Yes, the forces applied are enormous and excessive, but if I've read
>> it correctly these calculations talk about the force required to break
>> or tear the skewer from the dropouts.
>
> The calculations describe the forces in various directions, and resolve
> them to calculate the force acting directly in line with the dropout.
> The page compares that force with the standard. The standard is a
> minimum acceptable for a QR skewer. It says that in practice reasonably
> (not necessarily perfectly) adjusted skewers easily exceed the minimum.
> However, a skewer at the minimum leaves next to no margin.
>
> In practice, it would seem that the
>
>> QR skewers are NOT breaking or being torn from the dropouts. They are
>> coming open or loose first, and THEN the wheel is ejected. At least
>> that anectdotal account that you refer to indicates that the QR came
>> loose. Why is that? What is going on here to loosen the QR if that's
>> what happens?
>
>
> Brakes go on, brakes go off; the wheel grips the ground, the wheel
> skids, the wheel lifts off. The most difficult thing to model here is
> what happens when forces of this magnitude rapidly build up and then
> disappear. The forces are fluctuating wildly. What does this do to the
> adjustment on the skewer? It's not clear. All we know is the skewer is
> not made for that sort of battering; the forces act in an undesirable
> direction; and riders are reporting their skewers coming loose or even
> their wheels falling out.
>
>>
>>> Finally, if it is not connected with disc brakes, why is it riders of
>>> bikes with disc brakes that are reporting this problem?
>>
>>
>>
>> Good point. Trouble is that much of it is anectdotal evidence that
>> isn't easily replicated under controlled conditions to eliminate bias.
>> Maybe it has been happening with rim brakes? Maybe it is incorrectly
>> adjusted QR locks? Many features on modern mountain bikes are
>> relatively new. There are larger numbers of people riding modern
>> mountainbikes than ever before. I'm just not convinced that this
>> problem is entirely unrelated to incorrectly adjusted equipment for
>> the most part. I'm not sure how big this problem is in real life.
>>
> I agree with you that the data is inconclusive. It is also obvious that
> whatever the actual problem here, people do ride around on bikes with QR
> skewers and disc brakes without disaster. In so far as there is a
> problem, it is still unusual. But I would not want it to happen even
> once when I'm riding. Among other things, it's one of those problems
> that will only happen when you least want it, not when you're riding
> nice and gentle along flat smooth ground.
> [snip]
>
>>> There is at least one carefully written post in this thread from
>>> someone who was clearly very conscious of the potential for this
>>> problem. It describes a skewer that was correctly adjusted at the top
>>> of a hill being loose before the bottom of the hill. QR skewers are
>>> made to standards that do not take adequate account of the forces
>>> involved in common disc brake designs. So, its the combination of the
>>> two things: QR skewers that are designed for, and perfectly adequate
>>> with, rim brakes; and disc brakes that produce forces that
>>> dramatically increase the possibility that the skewer fails to retain
>>> the wheel.
>>
>>
>>
>> So why is that? The calculations went to the trouble of demonstrating
>> forces that are capable of ripping a correctly adjusted QR from the
>> drop-out or breaking it. But that doesn't seem to be what is
>> happening in reality. WHY did the QR become loose in this example and
>> NOT be ripped out? Maybe it's not the fault of the disc brakes, but a
>> fault of QR in general that is just becoming widely acknowledged?
>
>
> There is a substantial demonstrable difference in the forces from a disc
> brake, as opposed to a rim brake, that make it credible as part of the
> problem.

exactly why is it a problem? there's a substantial demonstrable force
on a bottom bracket that can cause separation if the spindle bolt is
not fastened correctly. likewise fork crowns can fatigue, hydraulic
brake lines can burst, you name it. last i read, annan's deliberately
sensationalist article chose the lowest pre-disk iso pullout rating,
equated that against braking force, then conveniently omitted any
investigation of actual pullout forces encountered in practice. if
you'd read in that same article that the actual pullout force exceeds
the resolved braking force by a factor of five, or even fifty if you
count lawyer lips, i doubt you'd be concerned.

fact: noone has yet posted any unequivocally proven cases of the axle
mounting being responsible for a wheel ejection. urls linking to some
guy that took a spill, which doesn't even discuss circumstances, let
alone equipment used, are _not_ unequivocal proof. read & understand
the manufacturer's instructions before using /any/ piece of equipment.
make sure you know how to tighten a q.r. properly!

conclusion: stop feeding the troll.

> My suggestion (I have no further evidence to back this up) to
> explain the observations is above. The fact that the standard for
> skewers is a minimum and the forces produced by the disc brake are
> around that minimum does, however, explain why the skewers do not simply
> break and are not simply instantly ripped out of the forks. The forces
> are still a considerable way short of breaking a skewer that is in good
> condition. Because a typical skewer can stand forces well in excess of
> the minimum the disc brake cannot not rip out the wheel until the skewer
> has been loosened to some extent. However, threaded fasteners loosening
> under violent vibration is not unknown.
>
> Maybe QRs have
>
>> been coming loose for years? Now that brakes have been developed
>> that will eject those loose skewers it's time to examine options to
>> secure the skewers and prevent them from coming loose in the first place.
>>
>> Regardless of the fault it does sound like it is time to take another
>> look at the design of systems used to hold the front wheel on.
>
>
> Agreed.
>
>

gcmschemist@gmail.com

JLB wrote:
>
> The principal facts I stated are:
> # the calculations show forces of a certain magnitude associated with

> disk brakes;

I don't think anyone who can read a vector diagram has any problem with
this part...

> # riders are reporting problems;

This part has a few problems, because the reporting does not include
information vital to assess the "why". This small, but very important,
detail is glossed over on the website. Without knowledge of initial
conditions and equipment used, the stories are mostly useless.

> # screw fasteners loosening under vibration is not unknown.

Unfortunately, this is a sort of "connect-the-dots" reasoning. As has
been mentioned before, a few different solutions for preventing
vibrational loosening are mentioned on the boltscience.com website.
Two of those are serrated fastener facings and "Nylock" nut inserts.

Shimano QRs use both of these anti-loosening technologies. If a
solution to the small possiblity of wheel ejection is to use Shimano
QRs, then why not go that route?

Anyway, the case for vibrational or load-induced loosening with respect
to QRs (and irrespective of brand and type,) has not been made with
hard, repeatable data. Until that occurs, I think that more hard,
repeatable data needs to be collected, and less anecdotal and possibly
apocryphal stories need to be repeated.

> I did not say it is a problem. I left it to the reader to decide if
that
> is a problem because I don't know. Do you?

How would you go about finding out?

> there's a substantial demonstrable force
> > on a bottom bracket that can cause separation if the spindle bolt
is
> > not fastened correctly. likewise fork crowns can fatigue,
hydraulic
> > brake lines can burst, you name it.
>
> Yes. What has this to do with disk brakes and qr skewers?

Directly, nothing. But as far as bicycling potential failure modes,
these all group in with disks/QRs.

[snip]

It does get to be a little troll-like after a while. I think there are
now over a thousand posts on this subject, and nobody is any closer to
even conclusively agreeing that there is a real-world problem (as
opposed to a theoretical one.)

HAND,

E.P.

Westie

JLB wrote:
> Westie wrote:
>
>> JLB wrote:
>
> [snip long discussion]

>>
>> So why is that? The calculations went to the trouble of demonstrating
>> forces that are capable of ripping a correctly adjusted QR from the
>> drop-out or breaking it. But that doesn't seem to be what is
>> happening in reality. WHY did the QR become loose in this example and
>> NOT be ripped out? Maybe it's not the fault of the disc brakes, but a
>> fault of QR in general that is just becoming widely acknowledged?
>
>
> There is a substantial demonstrable difference in the forces from a disc
> brake, as opposed to a rim brake, that make it credible as part of the
> problem. My suggestion (I have no further evidence to back this up) to
> explain the observations is above. The fact that the standard for
> skewers is a minimum and the forces produced by the disc brake are
> around that minimum does, however, explain why the skewers do not simply
> break and are not simply instantly ripped out of the forks. The forces
> are still a considerable way short of breaking a skewer that is in good
> condition. Because a typical skewer can stand forces well in excess of
> the minimum the disc brake cannot not rip out the wheel until the skewer
> has been loosened to some extent. However, threaded fasteners loosening
> under violent vibration is not unknown.

In my experience, there usually seems to be more violent vibration from
rim brakes under braking.

Without trying to drag a point out, I wonder if the fault is not with
the disc brakes but with these loosened skewers. Perhaps some, as yet
undefined, forces have been loosening skewers for years and it is only
now that disc brakes are being used (with their strong ejection forces)
that highlights the problem when it occurs. I guess it is possible that
accidents where the wheel has fallen from the fork occurred with rim
brakes also.

I know that the only time I have had a wheel fall off occurred when
using rim brakes and I performed a nose-wheelie stop. The rear wheel
fell out of the dropout as I came to a stop with the tail of the bike in
the air - Was it improperly adjusted QR? Was it snagged on the trail
and the QR loosened? It had been a rough trail, perhaps it was
vibration? I'll never know. All I can say is that in my mind the QR
was correctly adjusted shortly before the ride (I had changed a tube the
day before, rode it around the backyard, and double-checked the QR as I
tweaked derailleur adjustments).

If it is the QR that is the problem it is really a matter of semantics
whether you blame the QR or the brakes. Which came first, the chicken
or the egg?
--
Westie