Disc brakes and QRs making headlines



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[email protected] (Spider) wrote in message
news:<[email protected]>...
> James Annan <[email protected]> wrote in message
> news:<[email protected]>...

> > More evidence is always nice, but it's already proven beyond reasonable doubt IMO, let alone on
> > the balance of probabilities (the relevant confidence level in the UK).
>
> Proven beyond a shadow of a doubt???

I said 'reasonable', I don't do 100%, but I'm very close right now. Possibly it's a big conspiracy
and everyone has been lying and making up stories just to make me look foolish. There would have
been easier ways of achieving this, though.

> Where are the controlled studies? Please - a scientist accepts scientific analysis as proof. And
> controlled experiments need to be done.

Results from the test bench would not change my confidence. Data can be falsified, results
misintepreted, and I've already heard from a bunch of people who have seen it happen. A few more
wearing lab-coats won't make a difference.

Bear in mind that the appropriate level of confidence (in UK law) is the 'balance of probabilities'.
The current state of play (prior to 'lab tests') is that we have a large number of independent
experts agreeing on an obvious failure mode, and many users who report observing it with various
levels of detail. For the defence, there are a number of cyclists who say they haven't seen it
happen (yet). Well, Mr Juror, what is your verdict?

> A bunch of anecdotal evidence is STILL anecdotal.

Everything is anecdotal, unless you were there at the time, and I've rabbits come out of empty hats
and ladies sawn in half. I suspect that most of those demanding 'proof' do not work in scientific
research or they would not have such a rose-tinted view of the nature of the job, what counts as
'proof', and how it compares to what has been shown here.

> > The ultimate test of a theory is its ability to predict future outcomes, because that enables it
> > to be falsified or validated.
>
> Not merely "future outcomes," but "future outcomes conducted in a rigorous, controlled fashion."

That's a problem for climate scientists and atronomers, to name two. Shame, I thought my job was
somewhat worthwhile but now I learn it is pointless even in principle. Better now than 30 years down
the line, I suppose. Cheers!

James
 
True, setup of HS-33 is fickly, but after that maintenance is close to zero (new pads just click
in). Since they are much more powerful than ordinary rim brakes, the performance in wet weather is
good as well (my personal point of view), although not as good as disks. In short, best rim brake on
the planet (price and performance wise, although weight is very acceptable as well)

Caspar

"Jon Bond" <[email protected]> schreef in bericht
news:QITxa.647578$Zo.139498@sccrnsc03...
>
> "Caspar Lugtmeier & Eva Skotarczak" <[email protected]> wrote in
message
> news:[email protected]...
> > ....
> > > Cantis, which modulate but don't stop, or V-s, which stop but don't modulate...
> > ....
> >
> > Note that there is a rim brake that stops AND modulates: Magura HS-33
>
> Maguras are great breaks, but they have the same drawbacks for wet weather situations as any other
> rim brake, and my friend with them says they were something of a ***** to set up.
>
> Fantastic brakes for trials, though.
>
> Jon Bond
 
[email protected] (James Annan) wrote in message
news:<[email protected]>...
> [email protected] (Spider) wrote in message
> news:<[email protected]>...
> > James Annan <[email protected]> wrote in message
> > news:<[email protected]>...
>
> > > More evidence is always nice, but it's already proven beyond reasonable doubt IMO, let alone
> > > on the balance of probabilities (the relevant confidence level in the UK).
> >
> > Proven beyond a shadow of a doubt???
>
> I said 'reasonable', I don't do 100%, but I'm very close right now.

Indeed you did. My mistake.

> Possibly it's a big conspiracy and everyone has been lying and making up stories just to make me
> look foolish. There would have been easier ways of achieving this, though.

No need for sarcasm. You are taking this too personally. I am not attacking you or the data.

> > Where are the controlled studies? Please - a scientist accepts scientific analysis as proof. And
> > controlled experiments need to be done.
>
> Results from the test bench would not change my confidence.

Then you are doing this from faith. Every scientist will acknowledge experimental result over faulty
hypothesis.

> Data can be falsified, results misintepreted, and I've already heard from a bunch of people who
> have seen it happen. A few more wearing lab-coats won't make a difference.

Then why bother with a free-body diagram and math at all? If you already *know,* then why bother?

Sorry, James, but I don't accept using the word "proof" without actual *proof.* I'm kinda sticky
that way. :)

> Bear in mind that the appropriate level of confidence (in UK law) is the 'balance of
> probabilities'.

Now you are making a legal argument, and not a scientific one. But unfortunately, even with your
hypothesis, the accidents can be successfully challanged as "user error." While I agree with your
math, and your physics, I do not accept those things as proof of concept.

> The current state of play (prior to 'lab tests') is that we have a large number of independent
> experts agreeing on an obvious failure mode, and many users who report observing it with various
> levels of detail. For the defence, there are a number of cyclists who say they haven't seen it
> happen (yet). Well, Mr Juror, what is your verdict?

Where's the data? Where are the experiments that show that the hypothesis is correct? You can't just
present a hypothesis, have other people agree with the hypothesis, then say, "Yup, that's what
happened."

> > A bunch of anecdotal evidence is STILL anecdotal.
>
> Everything is anecdotal

Nonsense. When I conduct experiments with controls, and do statistics on the results, AND others can
repeat my experiments, I know what is "real" and what is not. And I have had quite a few poor
hypotheses stripped bare by experiment.

> I suspect that most of those demanding 'proof' do not work in scientific research or they would
> not have such a rose-tinted view of the nature of the job, what counts as 'proof', and how it
> compares to what has been shown here.

You have shown an interesting hypothesis, with some reasonable explanations of how it might occur.
As a chemist, I do not accept that as "proof," but as a supported hypothesis.

> > > The ultimate test of a theory is its ability to predict future outcomes, because that enables
> > > it to be falsified or validated.
> >
> > Not merely "future outcomes," but "future outcomes conducted in a rigorous, controlled fashion."
>
> That's a problem for climate scientists and atronomers, to name two.

But not for chemists and mechanical engineers. This is a mechanical engineering problem, and has
nothing to do with climatology or astronomy. Does it?

> Shame, I thought my job was somewhat worthwhile but now I learn it is pointless even in principle.
> Better now than 30 years down the line, I suppose. Cheers!

Again, save your sarcasm. AFAI concerned, you have a solid hypothesis, one that other science-minded
folks agree with. All that remains is the testing under rigorous conditions, such that "user error"
can be eliminated as a dismissal strategy.

BTW, I have a solution to the unscrewing. A washer with a tab that would go into the drop-out slots.
The washer would sit outboard of the springs, and the QR would not even go into the drop-out unless
the tab was in the correct orientation. That is, it would follow the axle into the drop-out.

That would not solve the QR strength issue, however.

Spider
 
In article <3Mw*[email protected]>, David Damerell
<[email protected]> wrote:

> We also know, if we ride with tandems, that they can brake as hard as single-seater bicycles in an
> emergency, and hence they can decelerate at 0.6g as well.

I know that a properly equipped tandem can decelerate even harder than a single bike, but with the
same lightweight braking system made for single bikes? In the past threads I've read that both
tandem and brake manufacturers advise against that and only few disks are certified for tandem use.
I wouldn't trust a 165mm XC disk on a tandem, honestly.

--
Fact of life #15: Heads bleed, walls don't.
 
"David Damerell" <[email protected]> wrote in message
news:3Mw*[email protected]...
> Maki <[email protected]> wrote:
> >because unless the braking system on the original single bike was *way* oversized this is not
> >what happens. To decelerate 160Kg at 0.6g you need a really powerful brake, not a 165mm one.
>
> Er, no. 0.6g is the point at which a single will lift the back wheel. We know that any bicycle
> with well-maintained brakes can brake that hard, because we've tried it. We also know, if we ride
> with tandems, that they can brake as hard as single-seater bicycles in an emergency, and hence
> they can decelerate at 0.6g as well.
> --
> David Damerell <[email protected]> flcl?

I don't know about you, David, but I can pop my back wheel up with only a little bit of pressure, or
put massive amounts of pressure on the brake and not have my rear wheel pop up. There's that whole
movable center of gravity and internal mass movement... the rider. Makes a big difference.

Jon Bond
 
"P e t e F a g e r l i n" <[email protected]> wrote in message
news:[email protected]...
> On Sun, 18 May 2003 21:54:38 GMT, "B. Sanders" <[email protected]> wrote:
>
>
> |> |> Plus I get more smooth braking than I did with Vs,
> |> |
> |> |Again, this is all about proper setup. Poorly setup V-brakes don't
> |modulate
> |> |well, and some stock pads (Shimano) are terrible. I hated V-brakes
until
> |I
> |> |got them setup correctly (just a wee bit of toe-in).
> |>
> |> Not in my experience. No matter how well you set up V-Brakes, they cannot modulate as well as
> |> properly setup discs.
> |
> |I'm here to tell you that they do. Much better. I was surprised when I
did
> |an A-B comparison, since I had read the hype about discs.
>
> And I'm here to tell you that your limited experience comparing Avid mechanical discs to one set
> of V-brakes is an extremely limited amount of experience.

Dude, I've been riding V-style brakes since *before* Shimano "invented" them (Wasatch). So don't
tell me about experience.

> Your claim that V-brakes modulate as well as discs is simply preposterous.

You can choose to ignore my claim since it differs from your cherished beliefs of disc superiority
for all conceivable offroad riding. So, where's that data showing disc superiority, Pete? You gonna
give up the goods, or pull a Bush and Co. and hide the "data"?

> |> You prior arguments about the relative costs of V-brake pads vs. disc pads are specious given
> |> the fact that disc pads last a very, very long time when compared to V-brake pads.
> |
> |Depends on the conditions and usage. When I need pads, it's nice to be
able
> |to find them almost anywhere. Discs are all different, making it likely |that pads won't be
> readily available for Brand X.
>
> ********. The bike shops that I've been in carry pads for most brands of discs, even
> aftermarket pads.

Not around here, they don't. Disc pads for Brand X calipers are *not* as common as AA batteries. Go
to any low-population area and try to find 'em.

> Do you live and ride in the middle of nowhere or something?

Many cyclists ride in remote areas, without sag support. That's why the smart ones choose
componentry that can be repaired *anywhere*. This means V-brakes are the logical choice (even
more than canti's). If you're a pro-rider with a support team following you around, ride
whatever you like.

Barry
 
"P e t e F a g e r l i n" <[email protected]> wrote in message
news:[email protected]...
> On Mon, 19 May 2003 20:31:09 GMT, "B. Sanders" <[email protected]> wrote:
>
> >"P e t e F a g e r l i n" <[email protected]> wrote in message
> >news:[email protected]...
>
>
> >> And I'm here to tell you that your limited experience comparing Avid mechanical discs to one
> >> set of V-brakes is an extremely limited amount of experience.
> >
> >Dude, I've been riding V-style brakes since *before* Shimano "invented"
them
> >(Wasatch). So don't tell me about experience.
>
> So comparing one set of discs, mechanical at that, to V-brakes is a comprehensive
> comparison, dude?
>
> p.s. I rode some before Shimano invented them as well, Marinovative.
>
> >> Your claim that V-brakes modulate as well as discs is simply preposterous.
> >
> >You can choose to ignore my claim since it differs from your cherished beliefs of disc
> >superiority for all conceivable offroad riding.
>
> Where did I write that, dude? I actually still ride a set of cantis off-road.

If that isn't your assertion, then what is your assertion? Just here to add noise? That's what
I thought.

> So, where's
> >that data showing disc superiority, Pete? You gonna give up the goods,
or
> >pull a Bush and Co. and hide the "data"?
>
> LOL. The "data" was shared with you in another post (German magazine) but the mere fact that you
> need "data" to believe that discs modualte better than V-brakes, when your only comparison is to a
> single set, and type, of discs, speaks volumes about your true intentions.

Nope. 3 different disc brakes on 4 different bikes (not just MTB). Many sets of V-brakes; though
only the Avids are clearly superior in modulation and power. I'm hooked on Avid's now.

The German magazine's results didn't draw any sweeping conclusions like "disc brakes are superior
for all types of offroad riding." It was clear from that data that V-brakes are the better choice
for anything but riding in extremely wet conditions. The V-brakes lost some power in the wet; but so
did some disc brakes. Not surprising. Certainly it wasn't at all conclusive about disc superiority,
even if we ignore the pad replacement, extreme expense and weight issues (which are not
insignificant to most riders). My conclusion: For those who ride in sloppy wet conditions all the
time, consider discs. For everybody else, save your money, unless you're curious. That's exactly
what I did: I was curious. Tried discs. They didn't live up to the hype. The magazine tests closely
matched my own experiences.

You're convinced that I couldn't possibly have better modulation with V-brakes. Maybe you just don't
know how to set them up properly? Or are you hiding more test results that clearly show disc
superiority for and every MTB riding application?

> >> |> You prior arguments about the relative costs of V-brake pads vs.
disc
> >> |> pads are specious given the fact that disc pads last a very, very
long
> >> |> time when compared to V-brake pads.
> >> |
> >> |Depends on the conditions and usage. When I need pads, it's nice to be
> >able
> >> |to find them almost anywhere. Discs are all different, making it
likely
> >> |that pads won't be readily available for Brand X.
> >>
> >> ********. The bike shops that I've been in carry pads for most brands of discs, even
> >> aftermarket pads.
> >
> >Not around here, they don't. Disc pads for Brand X calipers are *not* as common as AA batteries.
> >Go to any low-population area and try to find
'em.
>
> And where do you live that V-brake pads are as common as AA batteries? What a bizarre analogy.
> Does Walgreens sell V-brake pads on your planet?

Nearly every *Mart sells V-pads on my planet; but they don't sell pads for any brand of disc brakes.
What planet are you from?

> p.s. I actually found some Magura pads in a very low population are one year. Downieville, CA. Go
> figure.

Good thing you weren't riding Formula, Grimeca, Cyclone, Tektro or Hayes.

> >Many cyclists ride in remote areas, without sag support. That's why the smart ones choose
> >componentry that can be repaired *anywhere*. This means V-brakes are the logical choice (even
> >more than canti's). If you're a pro-rider with a support team following you around, ride
> >whatever you
like.
>
> Your posts just get more and more ridiculous.

Then ignore them, or make your point. What *is* your point, anyway? All you've done is prove your
arrogance over and over again. (Which didn't surprise most of us, I'm sure.)

Barry
 
"Jon Bond" <[email protected]> wrote in message
news:rMTxa.886035$3D1.505555@sccrnsc01...
>
> "B. Sanders" <[email protected]> wrote in message
> news:[email protected]...
> >
> > "Jon Bond" <[email protected]> wrote in message
> > news:bpTxa.885843$3D1.505911@sccrnsc01...
> > >
> > > "B. Sanders" <[email protected]> wrote in message
> > > news:[email protected]...
> > > > "P e t e F a g e r l i n" <[email protected]> wrote in message
> > > > news:[email protected]...
> > > > > On Sun, 18 May 2003 17:30:03 GMT, "B. Sanders"
<[email protected]>
> > > > > wrote:
> > > >snip<
> > > > > Properly set up discs modulate much better than V-brakes in my experience.
> > > >
> > > > We'll add your experiences to the data pool. snip<
> > >
> > > Data pool:
> > >
> > > People who think Discs are better, both in power and modulation, among
> > other
> > > things: A shitload.
> > >
> > > People who still insist that V's are superior: Barry.
> >
> > LOL! I love how you play right into my hands...
>
> Can anyone tell me who looks like the stubborn grouch here? Anyone?
Anyone?
> Bueler?
>
> > By avoiding facts, and marginalizing any detractors, you are showing how weak the pro-disc
> > argument is. Evidence? Facts? Tests? Where are
they?
>
> Facts: I gave you the weights, which you quickly ignored. Where are your facts, barry?

You see, I'm not the one evangelizing the new technology. You are. Burden of proof falls on you. Ok,
so at the extreme high end of superlight untouchably-expensive gear, disc brakes are only about
twice as heavy as V-brakes, instead of 4x as heavy. That's only one tiny part of the whole "discs
are superior" argument.

We're talking about braking superiority, in case you had forgotten (or were you just trying to avoid
answering the question?). So, where's that data proving that discs are better for any and all
offroad riding? Surely, you must have consulted some form of unbiased testing to formulate your
strong opinions.

> > What do you mean when you say "discs are better?" Do you mean lighter?
> Do
> > you mean cheaper? Do you mean simpler? What exactly do you mean?
>
> And I quote: "both in power and modulation, among other things"

Well, that's funny, because my personal tests disagree with that. So, show me the data that you're
referring to. You *do* have some, right?

-Barry
 
Spider wrote:

> Where's the data? Where are the experiments that show that the hypothesis is correct? You can't
> just present a hypothesis, have other people agree with the hypothesis, then say, "Yup, that's
> what happened."

I believe it is already safe to say that in happens, on the balance of probabilities. Anyone who
believes that it does not happen, on the balance of probabilities, is welcome to offer a substantial
wager to that effect.

Of course, I am confident that the data will be forthcoming, and it shouldn't take too long. The
only question is, do we all do nothing until the fork manufacturers work out how best to put a
public face on this problem (which will, I imagine, take a lot more thought than merely identifying
the flaw).

> This is a mechanical engineering problem, and has nothing to do with climatology or astronomy.
> Does it?

It's an analysis of an intermittent failure problem and therefore woulod be quite possible to miss
in inadequate lab testing. No Bridgestone tyres ever failed on a test rig, as far as I know. In the
sense that it is a probabilistic prediction, it may have more in common with climate science than
you think. It is clear that a large number of the "hasn't happened to me yet" brigade, and also the
guy who wants to see detailed accurate measurements of the unscrewing rate of a QR, do not
understand this point very well.

James
 
James Annan:

> Spider wrote:
>
> > Where's the data? Where are the experiments that show that the hypothesis is correct? You can't
> > just present a hypothesis, have other people agree with the hypothesis, then say, "Yup, that's
> > what happened."
>
> I believe it is already safe to say that in happens, on the balance of probabilities. Anyone who
> believes that it does not happen, on the balance of probabilities, is welcome to offer a
> substantial wager to that effect.

The operative word there is "believe".

> Of course, I am confident that the data will be forthcoming, and it shouldn't take too long.

Others don't share your confidence, mainly because your argument is not backed up by any solid
quantitiative theory.

> > This is a mechanical engineering problem, and has nothing to do with climatology or astronomy.
> > Does it?
>
> It's an analysis of an intermittent failure problem and therefore woulod be quite possible to miss
> in inadequate lab testing. No Bridgestone tyres ever failed on a test rig, as far as I know. In
> the sense that it is a probabilistic prediction, it may have more in common with climate science
> than you think. It is clear that a large number of the "hasn't happened to me yet" brigade, and
> also the guy who wants to see detailed accurate measurements of the unscrewing rate of a QR, do
> not understand this point very well.

This is a disingenuous argument. Comparing the Bridgestone tyre case to QR loosening mechanism, and
slapping an "unreliable" or "unnecessary" tag on any lab testing to quantify the mechanism proposed
because of the possibility of inadequacy of methodology is grasping at straws. It has nothing to do
with climate science, nor does it have any similarity to
it. Not being a mechanical engineer, you do not understand this point very well.

It's surprising to me that the flaw in your logic against quantitative analysis of QR loosening
cannot be made obvious to you by unemotive arguments from others. Having suffered from a disc brake
failure incident and wanting to push this issue as far as you can may have clouded your objectivity.

Answer me this simple question: can you show a quantitative analysis of the QR loosening mechanism
you propose, similar to the analysis you made on the forces involved with a disc brake system? When
you come up with a "no", tell me that it still surprises you that others express a desire for
empirical evidence based on testing.
 
"B. Sanders" <[email protected]> wrote in message
news:<[email protected]>...
> "Jon Bond" <[email protected]> wrote in message
> news:bpTxa.885843$3D1.505911@sccrnsc01...
> >
> > "B. Sanders" <[email protected]> wrote in message
> > news:[email protected]...
> > > "P e t e F a g e r l i n" <[email protected]> wrote in message
> > > news:[email protected]...
> > > > On Sun, 18 May 2003 17:30:03 GMT, "B. Sanders" <[email protected]> wrote:
> snip<
> > > > Properly set up discs modulate much better than V-brakes in my experience.
> > >
> > > We'll add your experiences to the data pool. snip<
> >
> > Data pool:
> >
> > People who think Discs are better, both in power and modulation, among
> other
> > things: A shitload.
> >
> > People who still insist that V's are superior: Barry.
>
> LOL! I love how you play right into my hands...

Heh. If by that you mean, "I love how you use logic to defeat my assertions," I guess that
would be true.

> By avoiding facts, and marginalizing any detractors, you are showing how weak the pro-disc
> argument is.

Sounds exactly like what you are doing.

> Evidence? Facts? Tests? Where are they?

Good call - where are *yours*? See, you are the one making a claim, a claim contrary to what
everyone else seems to have experienced. Therefore, it'd behoove you to prove your claim with DATA.

> What do you mean when you say "discs are better?" Do you mean lighter? Do you mean cheaper? Do you
> mean simpler? What exactly do you mean?

"Better" as in "less fade, better modulation, easier to set up and maintain, easier on the
bicycle system."

> > Dare to be different, Barry, dare to be different...
>
> Be a pack animal, Jon. Be just like all the other tattooed fashion victims. Don't ever stray from
> the norm. Mercilessly ridicule those who are different to boost your fragile ego.

Oddly, I don't see much ridicule from Jon, nevermind the "merciless" part. Use hyperbole much?

I never would have used disks either, but for a chance encounter with a bike that had Avid mechs on
it. My friend and I swapped bikes on a familiar run, so I could check out his rear der's performance
(or supposed lack.) My Avid Titanium Vs with Avid SD7 levers against his Avid mech disks and SD5
levers. According to you, my bike should have had better braking. But it didn't. The mech. disks
were a step up - and a significant one. But wait - here's where you trot out the old "if your Vs had
been properly set up..." without one shred of evidence to suggest they weren't. Other than the
circular "If they had been properly set up, then they would have been better" blah, blah, blah. Fact
is, I have been setting up bike brakes for literally decades. Center-pulls, side-pulls, Vs and now
disks. Now, if I do not deviate from what Barnett's has to say, what am I doing so wrong?

You don't have any data. All you have is your belief. And that's fine, as long as you recognize that
it's valid for an n=1. I have actually heard it suggested that Avid mechs are about as
bottom-of-the-barrel as disk brakes go. By my experience, they are much better than top-of-the-line
Avid Vs, and that means that the rest of the disk brake world offers even more benefits.

After my eye-opening ride, I went right out and bought a disk hub and mech disk set-up for my
hardtail (no rear mount.) It's better than the double-V set-up.

Spider
 
Jose Rizal <_@_._> wrote in message news:<[email protected]>...
> James Annan:

> > I believe it is already safe to say that in happens, on the balance of probabilities. Anyone who
> > believes that it does not happen, on the balance of probabilities, is welcome to offer a
> > substantial wager to that effect.
>
> The operative word there is "believe".

I rather prefer to focus on 'substantial wager' :)

> It's surprising to me that the flaw in your logic against quantitative analysis of QR loosening
> cannot be made obvious to you by unemotive arguments from others. Having suffered from a disc
> brake failure incident and wanting to push this issue as far as you can may have clouded your
> objectivity.

Maybe so, and I think that this part of the debate is getting a bit silly. Of course I don't object
to people performing the experiments and collecting data, so long as it does not delay them unduly
from taking approprite action. I was, however, asked if I personally thought the data were
necessary, and I personally do not.

> Answer me this simple question: can you show a quantitative analysis of the QR loosening mechanism
> you propose, similar to the analysis you made on the forces involved with a disc brake system?
> When you come up with a "no", tell me that it still surprises you that others express a desire for
> empirical evidence based on testing.

I'm not an expert myself, but from exchanges with people who are, and what I have read on the web,
it seems to be a widely known and well understood issue. You will by now have read the article on
www.boltscience.com, and also Jobst Brandt has given a succint summary here on at least one
occasion. Here's another description from Chris Juden:

"Whether we call it vibration or an intermittent force, a tiny crossways movement under a threaded
faster, often repeated, is enough to loosen it eventually. Everything is flexible to a degree: push
it one way and it springs back. That's how vibration loosening works. For instance the (stupidly
small) screws that secure rear luggage carriers to the dropouts. The weight of the luggage always
acts downwards but varies with roughness of the road, so that the carrier leg nevertheless jiggles
up and down, eventually loosening the screw. Yes it does. How long to do it (a million miles or a
hundred) just depends how heavy the load and how rough the road."

To save another round of potential misunderstanding, I'll point out the importance of the 'tiny
crossways movement' in the above. As I understand it, if the contact friction between bolt/nut and
clamped surface is not broken, the unscrewing will not occur at all even under significant shear and
vibration forces. That's why rim brakes do not cause the unscrewing - the forces do not overcome the
QR clamp friction. For that matter, a properly threadlocked bolt also won't unfasten, and my luggage
carrier is by now firmly corroded in place. But in the case of disk brakes, the friction is
overcome, and if the skewer thread is insufficiently stiff, unscrewing may well occur. I don't
really see what there is to 'prove' here, there is nothing new about this other than the realisation
that the necessary and sufficient preconditions apply in this situation.

James
 
"B. Sanders" wrote:
>
> Many cyclists ride in remote areas, without sag support. That's why the smart ones choose
> componentry that can be repaired *anywhere*. This means V-brakes are the logical choice (even
> more than canti's). If you're a pro-rider with a support team following you around, ride whatever
> you like.
>
> Barry

I have *NEVER* had SAG support on a mountain bike ride. <G>

Barry
 
Jon Bond <[email protected]> wrote:
>"David Damerell" <[email protected]> wrote in message
>>Er, no. 0.6g is the point at which a single will lift the back wheel.
>I don't know about you, David, but I can pop my back wheel up with only a little bit of pressure,
>or put massive amounts of pressure on the brake and not have my rear wheel pop up. There's that
>whole movable center of gravity and internal mass movement... the rider.

Thank you, Captain Obvious. Yes, that 0.6g does assume a fairly sane placement of the rider, that
you aren't carrying lead weights in your panniers, etc. None of this obviates the fact that James
Annan's 0.6g is a sensible figure for deceleration.

[However, if you can put "massive" pressure on your brake and not lift the back wheel, you should
adjust it.]
--
David Damerell <[email protected]> Kill the tomato!
 
Just look at this idiot's pride swell as he notes the large numbers of reponses to his posting.

--
Robin Hubert <[email protected]>

"James Annan" <[email protected]> wrote in message news:[email protected]...
> Spider wrote:
>
> > Where's the data? Where are the experiments that show that the hypothesis is correct? You can't
> > just present a hypothesis, have other people agree with the hypothesis, then say, "Yup, that's
> > what happened."
>
> I believe it is already safe to say that in happens, on the balance of probabilities. Anyone who
> believes that it does not happen, on the balance of probabilities, is welcome to offer a
> substantial wager to that effect.
>
> Of course, I am confident that the data will be forthcoming, and it shouldn't take too long. The
> only question is, do we all do nothing until the fork manufacturers work out how best to put a
> public face on this problem (which will, I imagine, take a lot more thought than merely
> identifying the flaw).
>
> > This is a mechanical engineering problem, and has nothing to do with climatology or astronomy.
> > Does it?
>
> It's an analysis of an intermittent failure problem and therefore woulod be quite possible to miss
> in inadequate lab testing. No Bridgestone tyres ever failed on a test rig, as far as I know. In
> the sense that it is a probabilistic prediction, it may have more in common with climate science
> than you think. It is clear that a large number of the "hasn't happened to me yet" brigade, and
> also the guy who wants to see detailed accurate measurements of the unscrewing rate of a QR, do
> not understand this point very well.
>
> James
 
Oops! This was aimed for Michael Pearlman and his "it's been X days now...". How it went here I
do not know.

--
Robin Hubert <[email protected]>

"Robin Hubert" <[email protected]> wrote in message
news:D[email protected]...
> Just look at this idiot's pride swell as he notes the large numbers of reponses to his posting.
>
> --
> Robin Hubert <[email protected]>
>
> "James Annan" <[email protected]> wrote in message
> news:[email protected]...
> > Spider wrote:
> >
> > > Where's the data? Where are the experiments that show that the hypothesis is correct? You
> > > can't just present a hypothesis, have other people agree with the hypothesis, then say, "Yup,
> > > that's what happened."
> >
> > I believe it is already safe to say that in happens, on the balance of probabilities. Anyone who
> > believes that it does not happen, on the balance of probabilities, is welcome to offer a
> > substantial wager to that effect.
> >
> > Of course, I am confident that the data will be forthcoming, and it shouldn't take too long. The
> > only question is, do we all do nothing until the fork manufacturers work out how best to put a
> > public face on this problem (which will, I imagine, take a lot more thought than merely
> > identifying the flaw).
> >
> > > This is a mechanical engineering problem, and has nothing to do with climatology or
> > > astronomy. Does it?
> >
> > It's an analysis of an intermittent failure problem and therefore woulod be quite possible to
> > miss in inadequate lab testing. No Bridgestone tyres ever failed on a test rig, as far as I
> > know. In the sense that it is a probabilistic prediction, it may have more in common with
> > climate science than you think. It is clear that a large number of the "hasn't happened to me
> > yet" brigade, and also the guy who wants to see detailed accurate measurements of the unscrewing
> > rate of a QR, do not understand

> > this point very well.
> >
> > James
> >
> >
 
"David Damerell" <[email protected]> wrote in message
news:qNC*[email protected]...
> Jon Bond <[email protected]> wrote:
> >"David Damerell" <[email protected]> wrote in message
> >>Er, no. 0.6g is the point at which a single will lift the back wheel.
> >I don't know about you, David, but I can pop my back wheel up with only a little bit of pressure,
> >or put massive amounts of pressure on the brake
and
> >not have my rear wheel pop up. There's that whole movable center of
gravity
> >and internal mass movement... the rider.
>
> Thank you, Captain Obvious. Yes, that 0.6g does assume a fairly sane placement of the rider, that
> you aren't carrying lead weights in your panniers, etc. None of this obviates the fact that James
> Annan's 0.6g is a sensible figure for deceleration.
>
> [However, if you can put "massive" pressure on your brake and not lift the back wheel, you should
> adjust it.]
> --
> David Damerell <[email protected]> Kill the tomato!

I know it was obvious, but it wasn't stated - I'm not arguing your number, I'm arguing the fact that
you've got a specific number for anything.

BTW, I can usually lock up my front brake on level surfaces and not have the rear come up - yeah,
the fork compresses like mad, but the wheel slides before the rear wheel comes up as long as I'm
movin' and groovin'. Then again, my tires are pretty worn right now.

Jon Bond
 
James Annan:

> Jose Rizal <_@_._> wrote in message
> news:<[email protected]>...
> > James Annan:
>
> > > I believe it is already safe to say that in happens, on the balance of probabilities. Anyone
> > > who believes that it does not happen, on the balance of probabilities, is welcome to offer a
> > > substantial wager to that effect.
> >
> > The operative word there is "believe".
>
> I rather prefer to focus on 'substantial wager' :)
>
> > It's surprising to me that the flaw in your logic against quantitative analysis of QR loosening
> > cannot be made obvious to you by unemotive arguments from others. Having suffered from a disc
> > brake failure incident and wanting to push this issue as far as you can may have clouded your
> > objectivity.
>
> Maybe so, and I think that this part of the debate is getting a bit silly. Of course I don't
> object to people performing the experiments and collecting data, so long as it does not delay them
> unduly from taking approprite action. I was, however, asked if I personally thought the data were
> necessary, and I personally do not.
>
> > Answer me this simple question: can you show a quantitative analysis of the QR loosening
> > mechanism you propose, similar to the analysis you made on the forces involved with a disc brake
> > system? When you come up with a "no", tell me that it still surprises you that others express a
> > desire for empirical evidence based on testing.
>
> I'm not an expert myself, but from exchanges with people who are, and what I have read on the web,
> it seems to be a widely known and well understood issue. You will by now have read the article on
> www.boltscience.com, and also Jobst Brandt has given a succint summary here on at least one
> occasion. Here's another description from Chris Juden:
>
> "Whether we call it vibration or an intermittent force, a tiny crossways movement under a threaded
> faster, often repeated, is enough to loosen it eventually. Everything is flexible to a degree:
> push it one way and it springs back. That's how vibration loosening works. For instance the
> (stupidly small) screws that secure rear luggage carriers to the dropouts. The weight of the
> luggage always acts downwards but varies with roughness of the road, so that the carrier leg
> nevertheless jiggles up and down, eventually loosening the screw. Yes it does. How long to do it
> (a million miles or a hundred) just depends how heavy the load and how rough the road."

The last sentence says it all. This is exactly what needs to be shown in the case of QRs loosening,
and one of my points all along. This is important, as even a slight rate of movement and loosening
will result in misalignment of caliper/rotor, and will be noticeable to the rider; therefore the
scenario of suddenly having the QR lever pop open or the wheel popping out of the dropout without
warning is not realistic. If the rate of loosening is great (and it's hard to believe that this is
the case, but it again depends on the QR tightness and braking loads), there will still be a
noticeable misalignment of the caliper/rotor prior to the QR clearing the fork lips. The anecdotal
data you present do not mention (much, if at all) the warning signs of loose QRs ie noticeable
caliper/rotor rub, and hence have the appearance that these operators all of a sudden just found
their QRs loose or their wheels ejected without notice. This is what needs to be cleared up.

> To save another round of potential misunderstanding, I'll point out the importance of the 'tiny
> crossways movement' in the above. As I understand it, if the contact friction between bolt/nut and
> clamped surface is not broken, the unscrewing will not occur at all even under significant shear
> and vibration forces.

This is obvious.

> That's why rim brakes do not cause the unscrewing - the forces do not overcome the QR clamp
> friction.

No, rim brakes do not cause this because there is nowhere for the axle to move - the reaction force
on the axle from rim braking has no component that acts along the dropout slot towards the ground.

> For that matter, a properly threadlocked bolt also won't unfasten, and my luggage carrier is by
> now firmly corroded in place. But in the case of disk brakes, the friction is overcome, and if the
> skewer thread is insufficiently stiff, unscrewing may well occur.

Which goes back to the issue above.

> I don't really see what there is to 'prove' here, there is nothing new about this other than the
> realisation that the necessary and sufficient preconditions apply in this situation.

"Can" apply in this situation. I never said there was anything new in the concept of threaded
systems loosening under cyclic motion, only that it still remains to be shown that this is what
happens in QR systems in the situation you describe. What is to be proved is whether this mechanism
can be made to happen in QRs/disc brake systems, thereby eliminating subjective data from anecdotes.

This mechanism is straightforward: loosening will occur if there is enough cycles of movement, or
large enough amplitudes of movement, or both. There is no magic random factor which will affect
this. The process of this mechanism happening, however, will cause effects which will serve as
warnings and which are not mentioned in the bulk of your anecdotal data. Hence the doubt whether the
anecdotal data is reliable enough.
 
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