Mavic MA-40 - Piece of Crap? - Page 6

BaCardi <usenet-forum@cyclingforums.com> writes:

>> Read page 2. Then come back and talk to me.

Ah, that explains it. BaCardi is Paul Harvey on a bender.

BaCardi <usenet-forum@cyclingforums.com> writes:

> And another thing. This is a technical newsgroup. Please let us know your arguments in favor of
> seamed rims. Since you are so heavily in favor of the old seams in rims, please let us know why.
> Compare weights. Compare cost. Compare cost per weight ratios. Finite Analysis is also desirable.

You're a little late to the party, mon. But Google can help you get caught up.

BaCardi wrote:
> ... Finite Analysis is also desirable.

I believe in Finite Analysis, since Infinite Analysis never reaches a conclusion.

Tom Sherman - 41½ N, 90½ W

jobst.brandt@stanfordalumni.org wrote:
> Well that depends on whether you have to do it 36 times to believe or if once is enough. Not
> everything has to be repeated to the limit to assess its results. For me one free joint is enough,
> for others two adjacent ones may be enough. I don't see doing it 36 times although if I had such a
> rim, it might be fun to do. The only problem would be making 36 zero thickness saw cuts.

sacrifice two rims and you can do it. i'm interested to see the result.

jb

jobst.brandt@stanfordalumni.org wrote: <snip>
>
> Hold the phone! Is there a discontinuity at the joint or a width variation, and how abrupt is it?
> This has the classic form of lies of the second kind, where the statement although accurate
> conveys an untrue message. Nowhere is there a mention of discontinuity in the rim in a misaligned
> rim joint that purportedly causes wheels to lock when braking. That the claimed lockup is untrue
> is apparent from the lack of end-over crashes cause by rims that aren't welded and machined.

just where exactly is the lie? have you ever /seen/ a cxp14 rim? have you examined its join? have
you ever measured one? don't just assume it's made the same as an ma2.

those are straight figures from braking surface caliper measurements. they may not suit your
preconceptions, but they are independently verifiable facts. just because something isn't convenient
does not make it a lie.

lies come from;

"experts" that know nothing of the dynamic properties of carbon composites but feel qualified to
postulate their vibration transmission inferiority.

"experts" that know nothing of work hardening differentials between mild and stainless steels, their
deformation & fatigue mechanisms but feel free to postulate radical theories of fatigue elimination
that would turn the entire materials world on its head.

"experts" that yet again know nothing about material deformation mechanisms but feel free to
postulate that plastic deformation of steel bearings is impossible.

"experts" that consider their materials knowledge superior to an entire industry of rim
manufacturers that dare to protect their product by anodizing, manufacturers that dump millions
into research. all because this "expert" reads a little about one of /many/ different possible
failure modes but feels by some strange intuition that the story stops there, further research is
irrelevant and that they are now suddenly qualified to apply this small subset of convenience to
all failures they see.

it's mysterious how such an "expert" has not similarly persecuted manufacturers of anodized hubs,
cranks, brakes, handlebars, forks, stems, seatposts, etc. funny how things work out.

"Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if
nothing had happened. -- Winston Churchill"

happy holidays.

Jim Beam writes:

>> Hold the phone! Is there a discontinuity at the joint or a width variation, and how abrupt is it?
>> This has the classic form of lies of the second kind, where the statement although accurate
>> conveys an untrue message. Nowhere is there a mention of discontinuity in the rim in a misaligned
>> rim joint that purportedly causes wheels to lock when braking. That the claimed lockup is untrue
>> is apparent from the lack of end-over crashes cause by rims that aren't welded and machined.

> Just where exactly is the lie? Have you ever /seen/ a CXP14 rim? Have you examined its join? Have
> you ever measured one? Don't just assume it's made the same as an MA-2.

You are dodging the question. Is there a discontinuity on the rim and does it cause brake problems.
Having ridden on severely damaged rims with no braking problems, I don't see what your recitation of
these measurements have to do with the question at hand. Juxtaposed with the discussion, they imply
proof for the need of machining, without evidence of a functional reason to do so. Therein is the
"lie of the second kind". You build your case on trusting or gullible readers to take your
statements of evidence as proof of your contention.

This is much like advertisements that put forth qualities of their product after saying "improve
your speed by 22.3 percent" there being no connection between that statement and the claims other
than proximity on the printed page.

> Those are straight figures from braking surface caliper measurements. They may not suit your
> preconceptions, but they are independently verifiable facts. just because something isn't
> convenient does not make it a lie.

The lie is the implication and, as I explained, these are "lies of the second kind". Your figures
may be accurate, although after having read your postings over time, I am even doubtful.

> Lies come from;

> "Experts" that know nothing of the dynamic properties of carbon composites but feel qualified to
> postulate their vibration transmission inferiority.

> "Experts" that know nothing of work hardening differentials between mild and stainless steels,
> their deformation & fatigue mechanisms but feel free to postulate radical theories of fatigue
> elimination that would turn the entire materials world on its head.

> "Experts" that yet again know nothing about material deformation mechanisms but feel free to
> postulate that plastic deformation of steel bearings is impossible.

> "Experts" that consider their materials knowledge superior to an entire industry of rim
> manufacturers that dare to protect their product by anodizing, manufacturers that dump millions
> into research. All because this "expert" reads a little about one of /many/ different possible
> failure modes but feels by some strange intuition that the story stops there, further research is
> irrelevant and that they are now suddenly qualified to apply this small subset of convenience to
> all failures they see.

> It's mysterious how such an "expert" has not similarly persecuted manufacturers of anodized hubs,
> cranks, brakes, handlebars, forks, stems, seatposts, etc. Funny how things work out.

This is a compendium of allusions to your expertise in these subjects although not explicitly
stated, Being placed in contrast to an implied expert who knows about these things, implies that
expert to be the speaker, or you. This is consistent with other things you have offered.

> "Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if
> nothing had happened. -- Winston Churchill"

Where's the beef. I saw no stitch of substance in this posting. These are truly "lies of the second
kind". I could not have constructed a better example.

Jobst Brandt jobst.brandt@stanfordalumni.org

Hear, hear !! An honest and competent expert shines by offering fact-based opinions, not personal
anecdotes, and just as much by honoring the limitations of his own expertise. Nasty words, hostile
repostes, and self-indulgent vanity don't make any sort of expert.

Bonne route,

Sandy Paris FR

"jim beam" <uce@ftc.gov>
--
a écrit dans le message de : news:92HGb.2361$vK1.390@newssvr25.news.prodigy.com...
> jobst.brandt@stanfordalumni.org wrote: <snip>
> >
> > Hold the phone! Is there a discontinuity at the joint or a width variation, and how abrupt is
> > it? This has the classic form of lies of the second kind, where the statement although accurate
> > conveys an untrue message. Nowhere is there a mention of discontinuity in the rim in a
> > misaligned rim joint that purportedly causes wheels to lock when braking. That the claimed
> > lockup is untrue is apparent from the lack of end-over crashes cause by rims that aren't welded
> > and machined.
>
> just where exactly is the lie? have you ever /seen/ a cxp14 rim? have you examined its join? have
> you ever measured one? don't just assume it's made the same as an ma2.
>
> those are straight figures from braking surface caliper measurements. they may not suit your
> preconceptions, but they are independently verifiable facts. just because something isn't
> convenient does not make it a lie.
>
> lies come from;
>
> "experts" that know nothing of the dynamic properties of carbon composites but feel qualified to
> postulate their vibration transmission inferiority.
>
> "experts" that know nothing of work hardening differentials between mild and stainless steels,
> their deformation & fatigue mechanisms but feel free to postulate radical theories of fatigue
> elimination that would turn the entire materials world on its head.
>
> "experts" that yet again know nothing about material deformation mechanisms but feel free to
> postulate that plastic deformation of steel bearings is impossible.
>
> "experts" that consider their materials knowledge superior to an entire industry of rim
> manufacturers that dare to protect their product by anodizing, manufacturers that dump millions
> into research. all because this "expert" reads a little about one of /many/ different possible
> failure modes but feels by some strange intuition that the story stops there, further research is
> irrelevant and that they are now suddenly qualified to apply this small subset of convenience to
> all failures they see.
>
> it's mysterious how such an "expert" has not similarly persecuted manufacturers of anodized hubs,
> cranks, brakes, handlebars, forks, stems, seatposts, etc. funny how things work out.
>
>
>
> "Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if
> nothing had happened. -- Winston Churchill"
>
>
> happy holidays.

No son. Try again. You've got nothing on Paul Harvey. Come back after you've done some legitimate research.

Google is just your calling. Give it a try.

BaCardi <usenet-forum@cyclingforums.com> wrote in message news:<fPRGb.6491$XQ2.6271@fe01-2.private.usenetserver.com>...
> Tim McNamara wrote:
> > You're a little late to the party, mon. But Google can help you get caught up.
>
>
>
> Google is just your calling. Give it a try.
>
>
>
Wow, it's not the usual witty, well thought out reply. I think the little guy's running out of gas.
Or more likely, it was past his bedtime.

Jeff

jobst.brandt@stanfordalumni.org wrote in message news:<%FHGb.4939$XF6.108373@typhoon.sonic.net>...

Dear Jobst and Jim,

As a bewildered layman, I'd like to ask a few obvious questions in hopes of learning more about what
I thought was the subject.

Which kind of rims provide better caliper braking, constant or varying width? How much better? That
is, at what point does varying rim width become noticeable when braking?

How much material is actually removed from machined rims compared to how much is left? Do
manufacturers compensate by making such rims thicker before machining, just as toilets are made
oversize to compensate for the way that they shrink in the kilns? (Sorry, but comparing rims to
toilets was irresistible.)

Does anodizing significantly weaken aluminum parts like rims, handlebars, and so forth? How?

How does anodizing affect braking, regardless of how the width of the rim varies?

Curiously,

Carl Fogel

Carl Fogel writes:

> Dear Jobst and Jim,

> As a bewildered layman, I'd like to ask a few obvious questions in hopes of learning more about
> what I thought was the subject.

Please stop this pseudo self deprecating style. Just ask the question.

> Which kind of rims provide better caliper braking, constant or varying width? How much better?
> That is, at what point does varying rim width become noticeable when braking?

I think that should be apparent. A step function, such as a lateral shift at a non-welded rim joint
causes an audible but non-functional brake noise. A sudden necking of the rim, in contrast, assuming
average friction in the brake cable, would make a pulsating brake retardation. However, a change in
rim width of a millimeter in a continuous cross section would not cause as much brake variation as a
drop of water on the rim, something commonly encountered by bicyclists.

> How much material is actually removed from machined rims compared to how much is left? Do
> manufacturers compensate by making such rims thicker before machining, just as toilets are made
> oversize to compensate for the way that they shrink in the kilns? (Sorry, but comparing rims to
> toilets was irresistible.)

I don't know anything about these cross sections, having only seen them displayed.

> Does anodizing significantly weaken aluminum parts like rims, handlebars, and so forth? How?

No, it doesn't but as I have often mentioned, it is a hard crust, just like a scab on a wound that
when stressed, cracks and causes bleeding on your knee or causes cracks to propagate into the
aluminum. Crack initiation is what causes the rim to fail and I use the scab analogy to make that
palpable for those who cannot play the Maxwell's demon and get right down into the psyche of the
metal surface.

> How does anodizing affect braking, regardless of how the width of the rim varies?

I thought you were the wizard of Google searches. This has been beat to death many times but it
seems to have more lives than a cat squared.

Anodizing is a ceramic insulator about half the density of aluminum, anodizing eats into the surface
about as much as it raises the surface of an aluminum extrusion. Heat in a friction pair is
generated in the surface of the softer material, in this case the "rubber" brake pad that is itself
an excellent insulator. Its only coolant is the aluminum rim that is an excellent conductor, has
large surface area, and is moving swiftly through the cooling medium, the atmosphere.

By coating the rim with ceramic, its heat absorption is diminished. Even a thin layer considering
the short residency of the pad at any location, looks to the hot surface of the brake pad like a
mirror, accepting little to no heat. Therefore, the surface temperature of the pad becomes hotter
than it normally would and thereby loses its designed drag coefficient against the braking surface.
For rim protection some dirt bike rims have ceramic coatings but require a different brake pad that
can take the heat. They also don't brake as well as common brakes when dry.

> Curiously,

I suppose.

Jobst Brandt jobst.brandt@stanfordalumni.org

Carl Fogel wrote:
> jobst.brandt@stanfordalumni.org wrote in message news:<%FHGb.4939$XF6.108373@typhoon.sonic.net>...
>
> Dear Jobst and Jim,
>
> As a bewildered layman, I'd like to ask a few obvious questions in hopes of learning more about
> what I thought was the subject.
>
> Which kind of rims provide better caliper braking, constant or varying width?

your phrasing implies you already have an answer carl.

two factors: amplitude of any difference length of any difference

an amplitude example is a "low spot" such as a wear indicator drilling. it's on a very small scale
compared to the brake pad and makes no detectable difference.

but if that were now a "high spot", suddenly you'd have wheel lock.

similarly, if the low spot is now large relative to the pad size, that becomes noticeable too. going
into the low spot is ok, but coming out again is the issue.

> How much better? That is, at what point does varying rim width become noticeable when braking?

a good question and i don't have an immediate quantitative answer for you. but we've all experienced
this in a qualitative way whether it be on a bike with a lumpy rim or a car with a warped rotor.
other than a bike with an old style rim, the only other application i can think of where braking
surfaces do /not/ rely on precision machined surfaces are old railroad brakes. but r/r wheels
sometimes develop flat spots and so these types of brakes suffer the same lockup problems as bikes.

>
> How much material is actually removed from machined rims compared to how much is left? Do
> manufacturers compensate by making such rims thicker before machining, just as toilets are made
> oversize to compensate for the way that they shrink in the kilns? (Sorry, but comparing rims to
> toilets was irresistible.)

good and somehow appropriate example. can't say how much gets machined off in practice, but if you
had a variance of say +/- 0.1mm, you'd have to machine off at least 0.2mm to ensure uniformity. and
of course, you'd make sure the unmachined component had correspondingly sufficient material to
allow this.

>
> Does anodizing significantly weaken aluminum parts like rims, handlebars, and so forth? How?

assuming that anodizing is the /only/ variable, it makes no difference to static strength but it
does to fatigue. it's the relevance that is debatable. if you have a rim whose braking surfaces
wears through in say 25,000 miles, how relevant is it that anodizing may reduce fatigue life from
50,000 miles to 45,000 miles?

>
> How does anodizing affect braking, regardless of how the width of the rim varies?

no figures, but my experience is that hard anodized braking surfaces are better in the wet because
the pads pick up less grit and therefore continue to be more effective.

>
> Curiously,
>
> Carl Fogel

jim beam wrote:

<snip>

>> Does anodizing significantly weaken aluminum parts like rims, handlebars, and so forth? How?
>
>
> assuming that anodizing is the /only/ variable, it makes no difference to static strength but it
> does to fatigue. it's the relevance that is debatable. if you have a rim whose braking surfaces
> wears through in say 25,000 miles, how relevant is it that anodizing may reduce fatigue life from
> 50,000 miles to 45,000 miles?
>

sorry, forgot the "how". anodizing can decrease fatigue performance because if it cracks, those
cracks act as stress concentrations. fatige can then initiate at those points.

but conversely, anodizing can protect significantly agains wear and corrosion and that can enhance
fatigue life.

jb

On Wed, 24 Dec 2003 05:47:54 GMT, jobst.brandt@stanfordalumni.org
wrote:

>Jim Beam writes:
>
>> [snip] And in what way is that worse than an unmachined braking surface habitually locking up at
>> the rim join - like my CXP14 does?

The CXP 14 rims I've built with are welded at the joint, but the sidewalls are not machined. It
looked to me as if the weld area had been sanded locally (about an inch either side of the weld).

That would explain Jim's CXP 14 rim that is narrower at the weld than elsewhere.

Sort of like the first Weinmann and Araya welded aluminum rims I can recall, the not-hollow ones
that fitted 27 x 1 1/4 tires.