Re: Marzocchi comes clean



A

Alien Rider

Guest
"Alien Rider" <[email protected]> wrote:

> "Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
> news:[email protected]...
>> Is 8" big or small for a disc? Maybe I need to think through
> it some more,
>> but visualizing the problem, my first impression is that
> smaller discs
>> should create larger ejection forces than larger discs.
>>
>> Andrew Lee
>
> This web page explains the problem with 8" rotors on standard
> forks:
>
> http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index.html
> http://makeashorterlink.com/?T538360A4
>
>

You have the math right in front of you and you still get it backwards?

Marzocchi obviously wasn't coming clean because they obviously don't
understand the problem at all.
 
Alien Rider wrote:
> "Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
> news:[email protected]...
>
>>Is 8" big or small for a disc? Maybe I need to think through
>
> it some more,
>
>>but visualizing the problem, my first impression is that
>
> smaller discs
>
>>should create larger ejection forces than larger discs.
>>
>>Andrew Lee
>
>
> This web page explains the problem with 8" rotors on standard
> forks:
>
> http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index.html
> 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.
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.

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.
--
Westie
 
Westie wrote:
> Alien Rider wrote:
>
>> "Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
>> news:[email protected]...
>>
This web page explains the problem with 8" rotors on standard
>> forks:
>>
>> http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index.html
>>
>> 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. Those calculations show clearly that a disc brake
set up produces different forces, both in magnitude and direction,
compared to rim brakes. It suggests that something like 2000N or more
can be acting on one side of the fork to push the wheel out. (For anyone
not too familiar with Newtons as a unit of force, this is not far off a
weight of one fifth of a ton.) Consider also that this force appears as
quickly as the brakes are applied; grab the brakes suddenly and there is
a dynamic or impulse effect. It also points out that the accepted
standard for QR systems leaves little or no margin with forces of this
magnitude.

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

> 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.

> --
> Westie


--
Joe * If I cannot be free I'll be cheap
 
On 13/12/04 9:43 am, in article [email protected],
"JLB" <[email protected]> wrote:


> 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.

I must admint that if[1] I were wanting to purchase a bike for serious off
road where I would be going down rough tracks at speed, I would most
certainly look for one with the captive front axles. It cannot be beyond the
ken of manufacturers to have a quick release mechanism that is not so
susceptible to this issue.

...d

[1] Big if. I am a bit of a coward when it comes to pain after a few nasty
skiing falls (track skis, hard ice with ruts in and down hill. My shoulders
appears to have finally got back to normal about 6 years on).
 
"Alien Rider" <[email protected]> wrote in message
news:[email protected]...
> "Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
> news:[email protected]...
> > Is 8" big or small for a disc? Maybe I need to think through
> it some more,
> > but visualizing the problem, my first impression is that
> smaller discs
> > should create larger ejection forces than larger discs.
> >
> > Andrew Lee
>
> This web page explains the problem with 8" rotors on standard
> forks:
>
>
http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index.html
> http://makeashorterlink.com/?T538360A4
>
>

Why don't they put the calipers on the front of the fork? Wouldn't that
reverse the force to an upward direction?

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

From Sheldon Brown's website:

"When quick-release wheels started being supplied on bicycles intended
for the general consumer market, ignorant users caused a rash of
accidents due to front wheels falling off. The resulting lawsuits led to
the addition of "lawyer lips" to most front forks, greatly reducing the
convenience of quick release wheels.

Recently there have been concerns about the safety of front disk brakes,
in conjunction with lightweight quick-release skewers. See James Annan's
article on this topic. "

http://www.sheldonbrown.com/gloss_q.html

Tony
 
David Martin wrote:
>
> I must admint that if[1] I were wanting to purchase a bike for serious off
> road where I would be going down rough tracks at speed, I would most
> certainly look for one with the captive front axles. It cannot be beyond the
> ken of manufacturers to have a quick release mechanism that is not so
> susceptible to this issue.
>

On a recent ride with a group of about 15 fairly serious riders - the
guys who built Seven Stanes and Afon Argoed - I counted all of them with
disc brakes and only two with non QR axles. All were aware of the issue.

Tony
 
Marty Wallace wrote:
> "Alien Rider" <[email protected]> wrote in message
> news:[email protected]...
>
>>"Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
>>news:[email protected]...
>>
>>>Is 8" big or small for a disc? Maybe I need to think through
>>
>>it some more,
>>
>>>but visualizing the problem, my first impression is that
>>
>>smaller discs
>>
>>>should create larger ejection forces than larger discs.
>>>
>>>Andrew Lee
>>
>>This web page explains the problem with 8" rotors on standard
>>forks:
>>
>>
>
> http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index.html
>
>> http://makeashorterlink.com/?T538360A4
>>
>>
>
>
> Why don't they put the calipers on the front of the fork? Wouldn't that
> reverse the force to an upward direction?
>
> Marty
>
>
this has been discussed before - all in the archives. fork legs are
castings, and castings in tension have significantly worse fatigue
properties than in compression. don't want the tabs breaking off do
you? just make sure the qr is done up properly. again, check the
archive for discussion on actual pullout force vs. that assumed in the
above.

this whole "chicken little" exercise in panic mongering makes about as
much sense as standing up in the middle of a busy airport and screaming
about wings falling off planes. wings can & do fall off planes, but

1. it doesn't happen in any statistically significant way, just like
there is no statistical preponderance of bike riders suffering wheel
ejection.

2. it'll never happen at all if the plane manufacturers maintenance &
inspection procedures are followed, just like if a skewer is properly
inspected and properly tightened before each ride per bike manufacturer
instructions.

there's only so much a manufacturer can do to save an idiot from
themselves. wearing a seatbelt in the car is smart, and legal penalties
exist for failure to use them, but crash fatality stats still show
plenty of darwin award candidates competing to leave the gene pool by
not wearing them. anyone ever ride without checking their qr?
 
Westie wrote:
> Alien Rider wrote:
>
>> "Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
>> news:[email protected]...
>>
>>> Is 8" big or small for a disc? Maybe I need to think through
>>
>>
>> it some more,
>>
>>> but visualizing the problem, my first impression is that
>>
>>
>> smaller discs
>>
>>> should create larger ejection forces than larger discs.
>>>
>>> Andrew Lee
>>
>>
>>
>> This web page explains the problem with 8" rotors on standard
>> forks:
>>
>> http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index.html
>>
>> 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.
> 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.
>
> 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.
> --
> Westie

the newbie comes in and cuts to the point immediately. nice job!
 
Tony Raven wrote:
> JLB wrote:
>
>>
>> Finally, if it is not connected with disc brakes, why is it riders of
>> bikes with disc brakes that are reporting this problem?
>>
>
> From Sheldon Brown's website:
>
> "When quick-release wheels started being supplied on bicycles intended
> for the general consumer market, ignorant users caused a rash of
> accidents due to front wheels falling off. The resulting lawsuits led to
> the addition of "lawyer lips" to most front forks, greatly reducing the
> convenience of quick release wheels.
>
> Recently there have been concerns about the safety of front disk brakes,
> in conjunction with lightweight quick-release skewers. See James Annan's
> article on this topic. "


.... that leads us to James Annan's article, the one that "Alien Rider"
quoted, which "Westie" picked up on, who I then replied to. So you
neatly take us back where we started.

--
Joe * If I cannot be free I'll be cheap
 
JLB wrote:
> Tony Raven wrote:
>
>> JLB wrote:
>>
>>>
>>> Finally, if it is not connected with disc brakes, why is it riders of
>>> bikes with disc brakes that are reporting this problem?
>>>
>>
>> From Sheldon Brown's website:
>>
>> "When quick-release wheels started being supplied on bicycles
>> intended for the general consumer market, ignorant users caused a rash
>> of accidents due to front wheels falling off. The resulting lawsuits
>> led to the addition of "lawyer lips" to most front forks, greatly
>> reducing the convenience of quick release wheels.
>>
>> Recently there have been concerns about the safety of front disk
>> brakes, in conjunction with lightweight quick-release skewers. See
>> James Annan's article on this topic. "
>
>
>
> .... that leads us to James Annan's article, the one that "Alien Rider"
> quoted, which "Westie" picked up on, who I then replied to. So you
> neatly take us back where we started.
>

but via the fact that front wheels fell out before disk brakes even
existed for bikes.

Tony
 
Tony Raven wrote:
> JLB wrote:
>
>> Tony Raven wrote:
>>
>>> JLB wrote:
>>>
>>>>
>>>> Finally, if it is not connected with disc brakes, why is it riders
>>>> of bikes with disc brakes that are reporting this problem?
>>>>
>>>
>>> From Sheldon Brown's website:
>>>
>>> "When quick-release wheels started being supplied on bicycles
>>> intended for the general consumer market, ignorant users caused a
>>> rash of accidents due to front wheels falling off. The resulting
>>> lawsuits led to the addition of "lawyer lips" to most front forks,
>>> greatly reducing the convenience of quick release wheels.
>>>
>>> Recently there have been concerns about the safety of front disk
>>> brakes, in conjunction with lightweight quick-release skewers. See
>>> James Annan's article on this topic. "
>>
>>
>>
>>
>> .... that leads us to James Annan's article, the one that "Alien
>> Rider" quoted, which "Westie" picked up on, who I then replied to. So
>> you neatly take us back where we started.
>>
>
> but via the fact that front wheels fell out before disk brakes even
> existed for bikes.

But Sheldon's article describes a problem that inexperienced riders had
with this unfamiliar technology when it became generally available, and
how it was (largely) solved. Sheldon then goes on to the concern about
disk brakes and QR skewers; not a general continuing concern about QR
skewers per se. So the present dicsussion is specific to disk brakes
with QR skewers, even in Sheldon's page, and my comment stands.


--
Joe * If I cannot be free I'll be cheap
 
JLB wrote:
>
>
> But Sheldon's article describes a problem that inexperienced riders had
> with this unfamiliar technology when it became generally available, and
> how it was (largely) solved.

It was largely solved, not by solving the misuse/design of QRs but by
adding on an extra bit so that even a misused QR should not lose a
wheel. As a result there are still a lot of misused QRs out there that
people have become used to getting away with. A quick spot check even
with experienced riders shows lots of bad practice - QR's not done up
over centre, levers pointing forward where they can get hooked open and
a whole variety of closing forces from flip with your little finger to
stand on them. The need to unscrew them all the time to take the wheel
out and in means that there is a greater chance of a setting error.

Tony
 
Tony Raven wrote:
> JLB wrote:
>>
>>
>> But Sheldon's article describes a problem that inexperienced riders
>> had with this unfamiliar technology when it became generally
>> available, and how it was (largely) solved.
>
> It was largely solved, not by solving the misuse/design of QRs but by
> adding on an extra bit so that even a misused QR should not lose a
> wheel. As a result there are still a lot of misused QRs out there that
> people have become used to getting away with. A quick spot check even
> with experienced riders shows lots of bad practice - QR's not done up
> over centre, levers pointing forward where they can get hooked open
> and a whole variety of closing forces from flip with your little
> finger to stand on them.

This varies by skewer, too. Specialized skewers are horribly designed, with
tiny levers that force the weak to apply a lot of force to close the skewer
properly. And the external cam itself has a profile such that a large
portion of the 90-degree pressure is lost when it is closed to 180 degrees.
Shimano skewers are definitely superior, with the palm-friendly concave
shape, large surface area, and internal (correctly shaped) cam.

And if you have seen most of the Specialized road bikes frames for 2004 and
2005, you'll notice that most of them don't have dropout material below 9
and 3-o-clock, lessening clamping force, and possibly even predisposing the
skewer to failure, due to the asymmetrical forces.

--
Phil, Squid-in-Training
 
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
 
Pete Jones wrote:


>
> http://www.bikemagic.com/forum/forummessages/mps/dt/4/UTN/62150/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/forum/read.php?f=2&i=1450407&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/
 
James Annan wrote:
> Pete Jones wrote:
>
>
>>
>> http://www.bikemagic.com/forum/forummessages/mps/dt/4/UTN/62150/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
 
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
 
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