CPSC judgement on disk brakes and QR forks



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D

Doug Taylor

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sti[email protected] (James Annan) wrote:

>Of course if someone comes back to them with any new evidence, they might reopen the case. The ASTM
>said several months ago that they would look into this 'in due course' but they do not seem to have
>done anything in the interim and are certainly not a consumer protection organisation. More likely,
>they will invent a new inconvenient wheel attachment method, foist it on all cyclists including
>road bike users, and I'll get blamed for that too.

It's all about YOU, eh, James?

BTW, this post comes closer to the definition of "troll" than those to which you have referred
recently. Save it for future reference. --dt
 
S

Spider

Guest
David Damerell <[email protected]> wrote in message
news:<4wu*[email protected]>...
> Spider <[email protected]> wrote:
> >who are new to the subject* and some are not. Like I said - I saw the number explained in *one*
> >place, after doing a groups search.
>
> You saw it explained _to you_ _right here_. Twice.

You keep repeating that like it means something.

I am going to assume that you are not being deliberately obtuse, and will explain my concern
stepwise, such that you may grasp the concept fully. I have obviously not made myself clear, which I
will apologize for in advance.

1.) This issue is of interest to may MTBers, due to equipment specifications on our bikes.

2.) Mr. Annan has been kind enough to point out a potential problem with the set-up involving disk
brakes, and goes to great lengths to support the hypothesis with stepwise reason and math.

3.) Not all of the questions that folks new to the discussion have plainly evident answers on the
website. In fact some numbers are not explained, and as such, people may wish to know the source
of those numbers.

4.) Such a number is "0.6g."

5.) The responses in this newsgroup to some of the questions unanswered on Mr. Annan's website
have been of the order of "do a google search." In some cases, google searching does not turn up
real answers.

6.) The conclusion should be that Mr. Annan's website does not include all the information necessary
in order to fully educate those new to the discussion. This leads to some consternation on the
part of James, and yourself (obviously) because of the style of answers.

Mr. Damerell, I am not concerned in the least with how many times you have "kindly" explained it to
*me*, but with those folks who come after me, who might wish to know. While you may not be able
to grasp this salient point, I am trying to save both you and Mr. Annan the frustration of
having to explain it again, to some new guy.

Now, if this is not clear to you, I will say it one more time - it matters not at all how many times
you explain it to me, because that is not my objection. My objection is that the number is not
explained on the website, while all the others are. IOW, it's not about *me*, but the numbers and
what they represent. Does this make sense, or must I reiterate?

Spider
 
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Spider

Guest
Joe Riel <[email protected]> wrote in message news:<[email protected]>...
> Joe Riel <[email protected]> writes:
>
> > For example, assume on a dirt trail mu = 0.5. The max steady state braking deceleration is
> >
> > amax = max(0.6g, 0.5g) = 0.5g.
>
> That should be
>
> amax = min(0.6g, 0.5g) = 0.5g.

Thank you for the explanation.

Finally, someone who can enlighten while refraining from smug, sneering condescension.

Is it any wonder that there is opposition to the hypothesis?

[rolls eyes]

As an addendum - my personal experience over the years of riding bikes on the dirt is that mu is
low, BUT can be variably high. It is part of what is attractive about riding a bike on the dirt -
you have to keep your concentration up at all times, or life will treat you poorly. :)

I still want to do the experiment with various surfaces to find the mu for each. It would be
interesting to see how often the ejection forces actually reach the peaks that James suggests.

Spider
 
T

Tim McNamara

Guest
In article <6Yr*[email protected]>, David Damerell
<[email protected]> wrote:

> Tim McNamara <[email protected]> wrote:
> >brake and the tire. Now, leaving out the weight of the bike for the sake of convenience, I make
> >that out to be an ejection force of: 200 * 0.6 = 120; 120 * 4 = 480 lbs of ejection force.
>
> Metric, man!

Sorry, I guess I'm just a hidebound American who thinks a Newton is just fruit and cake... ;-) Heck,
I rode the Alps last year and PBP this year with the computer set on "miles" rather than
"kilometers."

Thanks to all for straightening out my understanding on this point.
 
T

Tim McNamara

Guest
In article <[email protected]>, [email protected] (Spider) wrote:

> Now, if this is not clear to you, I will say it one more time - it matters not at all how many
> times you explain it to me, because that is not my objection. My objection is that the number is
> not explained on the website, while all the others are. IOW, it's not about *me*, but the numbers
> and what they represent. Does this make sense, or must I reiterate?

This seems altogether different than your previous posts on the matter.
 
J

Jobst Brandt

Guest
David Damerell writes:

>> It is hard predict where riders will position their CG when braking, which depends on rider skill
>> and aggressiveness, the g-force can lie in a fairly broad range, 0.6 being at the conservatively
>> low end. Although trails are hard and dusty, there are many regions where trails are moist and
>> knobby tires make an giving rise to traction greater than 1:1.

> Hang on - 2 postings ago you were talking about 0.6g of deceleration. Now you're talking about the
> coefficient of friction.

It has an important role but is not the only criterion. For example, consider riding on a frozen
lake where the traction is so poor that .1g is not possible. In such a setting, there is no
separation force. Let's not forget, when calculating the separation force of the axle, 1) it acts
only on one end of the axle, 2) the downward force from the load on the fork must be subtracted from
the separation force to be realistic (as I explained in earlier postings).

> The figure for deceleration is a sensible one to have in the discussion because it is a
> deceleration that riders may reach in an emergency stop without special positioning on the bike,
> and as such the resulting ejection force is one that may realistically be seen.

Not so. Even on fairly loose but uneven ground deceleration of 1g is likely. Average loadings are
fine, but this action responds to impact forces.

> That coefficient of friction entered the discussion at all is unfortunate, yes, since it is
> evident that often in emergency stops there is no risk of skidding the front wheel before the rear
> wheel lifts.

That is only in so much as it confuses the issue. That peak brake forces are at the level of 1g is
adequate for solving the problem, trying to reduce that is only a cover-up of the problem. I often
see riders descending on trails over rough stuff that makes them airborne between hard skids that
hammer away at their bicycle. These are easily 1g forces on the front wheel. For locals to my area,
that would be descending the Forest of Nisene Marks main trail, a hard surface rocky former logging
road and railroad incline.

http://www.parks.ca.gov/default.asp?page_id=666

Jobst Brandt [email protected]
 
J

James Annan

Guest
[email protected] wrote:

> Not so. Even on fairly loose but uneven ground deceleration of 1g is likely. Average loadings are
> fine, but this action responds to impact forces.

> That is only in so much as it confuses the issue. That peak brake forces are at the level of 1g is
> adequate for solving the problem, trying to reduce that is only a cover-up of the problem.

I agree with this, and the likelihood of higher peak loading has come up a few times previously.
Nevertheless, I think it helps most people to understand if they can actually 'see the numbers'
on this issue, and can you imagine the consternation if I had used a figure of 1g? I shudder to
think of it.

It's quite fortunate in that respect that the 0.6g figure can actually exceed the ISO standard, even
though neither is of great importance to the problem other than as a rough indicator of real-world
applicability.

James
 
S

Spider

Guest
Tim McNamara <[email protected]> wrote in message
news:<[email protected]>...
> In article <[email protected]>, [email protected]
> (Spider) wrote:
>
> > Now, if this is not clear to you, I will say it one more time - it matters not at all how many
> > times you explain it to me, because that is not my objection. My objection is that the number is
> > not explained on the website, while all the others are. IOW, it's not about *me*, but the
> > numbers and what they represent. Does this make sense, or must I reiterate?
>
> This seems altogether different than your previous posts on the matter.

Then you have not read them carefully. Part of my concern *all along* was the manner in which
questions were answered. If one desires to make a favorable impression, it behooves that person to
try and avoid being a complete asshole. Now, that's just my opinion, of course. Maybe out there in
the great wide world, this is SOP to treat everybody without the keenest of insight as a complete
moron. I've never come up against that myself, but I work in the sheltered community of a research
university.

The other part of my concern was about the actual questions themselves. The fact that I had to wait
so long for such a simple answer speaks volumes toward the other part of my concern.

Now, Tim, if you would like, I'll go back and start from the beginning and quote my style objections
on a post-by-post basis.

Spider
 
T

Tim McNamara

Guest
In article <[email protected]>, [email protected] (Spider) wrote:

> Tim McNamara <[email protected]> wrote in message
> news:<[email protected]>...

> > This seems altogether different than your previous posts on the matter.
>
> Then you have not read them carefully.

There's the "if you disagree with me then you haven't read carefully" strategem. Which is usually
shortly followed (as in your last paragraph) by the "you must be a moron so I'll spell it out in
baby talk for you."

> Part of my concern *all along* was the manner in which questions were answered. If one desires to
> make a favorable impression, it behooves that person to try and avoid being a complete asshole.
> Now, that's just my opinion, of course. Maybe out there in the great wide world, this is SOP to
> treat everybody without the keenest of insight as a complete moron. I've never come up against
> that myself, but I work in the sheltered community of a research university.

And of course you are not at all guilty of doing exactly the same thing from your earliest posts on
the subject. </sarcasm> Perhaps you haven't noticed that "treat(ing) everybody without the keenest
of insight as a complete moron" *is* SOP in the research university world. And you've learned your
lessons well.

> The other part of my concern was about the actual questions themselves. The fact that I had to
> wait so long for such a simple answer speaks volumes toward the other part of my concern.

The question was answered a number of times by Annan, Brandt and Dammerell, but you didn't seem to
notice. And, now that I think of it, you've yet to acknowledge that the question was answered.

> Now, Tim, if you would like, I'll go back and start from the beginning and quote my style
> objections on a post-by-post basis.

Thanks for showing that you're just as human and concescending as anyone else in this newsgroup.
Irritation and frustration are universal human characteristics.
 
D

David Damerell

Guest
Spider <[email protected]> wrote:
>Maybe out there in the great wide world, this is SOP to treat everybody without the keenest of
>insight as a complete moron.

So who was telling me to review my "freshman physics" (of something I learned at around age fifteen,
no less) while in fact talking rubbish himself?

This holier-than-thou attitude won't wash; you've been just as condescending, with the additional
drawback that you don't know what you're talking about.

--
David Damerell <[email protected]> Distortion Field!
 
S

Simon Brooke

Guest
[email protected] (James Annan) writes:

> "Doug Taylor" <[email protected]> wrote in message
> news:<[email protected]>...
>
> > As for you, please supply the name, date and place for *any* cyclist who has been severly
> > injured, paralyzed or killed due to your pet problem. Bet you can't find one.
>
> www.russ-appeal.org.uk is perhaps the most well-known, and provided much of the motivation for my
> research.
>
> I've heard of about 20 cases of actual wheel loss, roughly half of which have resulted in
> overnight (or longer) hospital stays - in the cash-strapped UK National Health Service, this is
> something that is far from routine and indicates that there were severe head and neck injuries.

There's serious misinformation here. The UK health system, like any other, could do with more money
than it has, but this doesn't limit overnight stays. In June of this year I was kept in for five
days for observation because of a blood clot in my leg. People with suspected concussion are almost
always kept in hospital at least twenty four hours for observation, so an overnight stay is no
indication of anything more than a minor bump on the head.

This isn't to say I have any opinion one way or the other regarding ejecting front wheels; merely
that the paragraph quoted doesn't provide any evidence of repeated serious injuries. Nor, on the
evidence I can find on the Russ Appeal site, is there conclusive evidence that the disk brake caused
the wheel to eject in Russell Pinder's accident - again, there may be evidence I don't know about -
but you have to remember that front wheels have been falling off bikes for a lot longer than we've
been using disk brakes.

--
[email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; I'll have a proper rant later, when I get the time.
 
J

James Annan

Guest
Simon Brooke <[email protected]> wrote in message
news:<[email protected]>...
> [email protected] (James Annan) writes:
>
> > I've heard of about 20 cases of actual wheel loss, roughly half of which have resulted in
> > overnight (or longer) hospital stays - in the cash-strapped UK National Health Service, this is
> > something that is far from routine and indicates that there were severe head and neck injuries.
>
> There's serious misinformation here. The UK health system, like any other, could do with more
> money than it has, but this doesn't limit overnight stays. In June of this year I was kept in for
> five days for observation because of a blood clot in my leg. People with suspected concussion are
> almost always kept in hospital at least twenty four hours for observation, so an overnight stay is
> no indication of anything more than a minor bump on the head.

Good grief, hasn't everyone on this thread packed up and gone home long ago?

Ok, I agree that the mere fact of an overnight stay does not in itself prove beyond any doubt that
the injuries were very serious. Nevertheless, many of the injuries _were_ very serious, I just
couldn't be bothered listing them all. They are not just a handful of the comedy over-the-bar
moments that most MTB riders will have learnt to love.

As an aside, I didn't think that an overnight stay was routine for mere concussion, let alone
`suspected concussion'. But I'll take your word for it, and it may even apply to one of the cases I
have heard about.

James
 
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Gary Young

Guest
James Annan <[email protected]> wrote in message news:<[email protected]>...
> This is not actually the 'official' signed letter which is in the post, but I received the
> following via email recently:
>
> "Based upon the information currently available, the staff does not believe the problem identified
> necessitates further action by the Commission under Section 15 of the CPSA. However, the
> Commission has recommended that the ASTM Bicycle Committee, which meets in October 2003, take this
> matter under advisement for further discussion, additional testing and problem examination."
>
> Section 15 of the CPSA can be found at https://www.cpsc.gov/businfo/cpsa15b.html
>
I thought the following article might be pertinent to this discussion:

<http://seattlepi.nwsource.com/business/apbiz_story.asp?category=1310&slug=Bicycle%20Defects%20Fine>

In a nutshell: a manufacturer of cheap department store bikes was fined US $1 million by the CPSC
for failing to report injuries caused by defective forks. I suppose it's reassuring to know the CPSC
is capable of taking strong action, even if it is after the fact. Perhaps that will motivate fork
makers to address the problem with disk brakes.
 
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