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Mad Roger Mad Roger is offline
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Default Need help INTERPRETING these test results police cruiser SAE J866a Chase Test

On Thu, 11 Jan 2018 11:44:01 -0500,
Clare Snyder wrote:

I'm discounting conterfeit parts as being the problemin these tests -
just going back to your "trust" in "government mandated markings" from
your previous thread.


I agree with you that it's unlikely that the police in Michigan were
testing counterfeit parts, especially as they apparently received the
friction material directly from the manufacturer, according to their
summary paper.

(We could fall prey to "ringers" though...)


No, I'm just saying - again - that depending on the government
mandated friction rating markings will NOT get you the best brake -
which has been my thesis from the beginning and has been proven by TWO
law enforcement vehicle tests you have provided to support your
position.


I'm not disagreeing with your contention that the EE pads, in those police
tests, somehow worked better than the FF pads, even though E is a friction
coefficient only marginally higher than steel on steel.

I'm only asking why.

I'msorry, but your thesis does NOT stand the test of proof using the
scientific method. You are an engineer. What does that tell you???


I'm an electrical engineer; so I believe in friction, but if the lower
friction coefficient pads are working better than the higher friction
coefficient pads, the precise understanding of that is out of my league.

That's why I asked here, where I was hoping the s.e.r intelligentsia might
help us rationalize a reason that stands the test of logical analysis.

If it was just a case of FF pads on a dodge undeperforming the same
pad on a Foprd, you could put it down to brake design - but that is not
the case here., There is NO LOGICAL EXPLANATION other than the FACT
that the markings are NOT a reliable predictor of brake performance -
muchless quality.


I agreed with your assessment, and I even quoted the Michigan police
cruiser test warning saying that the markings don't necessarily conform to
real-world practice.

I'm only asking here WHY an E coefficient pad (which is basically no pad at
all) performed better than an F coefficient pad (which has an appreciably
higher cold & hot friction coefficient)?

I puit more weight on the other qualities,as they are readilly evident
- while the friction grade of the material is not - as proven by the
tests.


I'm going to have to somewhat reluctantly agree with you, unless we get a
good reason, that no pad at all (i.e., just metal on metal) is "just as
good" and "maybe even better" than a high friction coefficient pad.

Pretty much that says "all pads work", does it not?

But how do you know that from the numbers printed on the pad?


You don't.


Again, I'm going to have to somewhat reluctantly agree with you, from a
logical standpoint, that if essentially no pad at all (i.e., an E
coefficient pad which has a coefficient of friction marginally better than
steel on steel) is better or about as good as having a pad, then almost
nothing printed on the side of the pad is going to make any difference.

Now another thing that affects HOT braking is the attachment of the
lining to the shoe/pad. Does the "glue" adequately transmit the heat
or act as an insulator?? Personally,I'm a BIG fan of rivetted linings
and pads, rather than bonded.


It seems there *must* be other *major* factors in braking performance,
other than the friction rating of the pads themselves.

That's a hard logical pill to swallow, for me, which is why I asked here,
hoping the s.e.r folks can enlighten us as to why.

Failure of the testing/certification process to reflect real world
conditions.


Well, the friction coefficient is a "real world" measurement.

It just doesn't seem to matter in braking performance, based on that police
cruiser test I unearthed.

That's too bad, because it means you can't compare pads easily other than
to note the material, type, and manufacturer, which the DOT CODES printed
on each pad and shoe do tell you.

So at least we can tell three pads with three different marketing
strategies (e.g, Axxis, PBR, & Metal Masters) are the exact *same* pad, and
we can tell when a pad is rebranded (I think Centric only does rebranded
pads, for example, but I'd have to check the numbers to be sure).

That indicates there is some utility in the mandated information that is
printed on the side of each pad.

But it's just sad that the friction coefficient means so little to a
friction material!

Sorry, but you engineers devise the tests. There is definitely
SOMETHING wrong with either the design of the test, the implementation
of the test, (application) or the theory applied.


Friction is friction.
It's a mathematical beast.

I don't think the SAE J866 Chase Tests lie about the friction of a 1"
square piece of the friction material.

They just don't predict real-world performance, it seems.
(As noted in the Police Cruiser report.)

Which is why I put very limited weight on the stamped/published
friction ratings.


Again, I must reluctantly agree with you, as hard a pill as it is to
swallow, that friction coefficients are NOT an important factor in the
performance of brake friction materials.

Sigh.

I just want to know WHY?

They have been proven time and again to be pretty close to useless.


Well, as I said, the *numbers* printed on the side of every pad/shoe sold
in the USA are *useful* in that they tell you the manufacturer, the
material, and, the friction rating - so even if we discount the friction
rating, it's nice to know when you can tell that two pads sold and marketed
at two different prices, are the same pad.

Now, if you take a, for instance, BRakebond pad with ee, another of
their pads with ef, and another eith ff - there MIGHT be a displayable
progression between them - all other factors being the same (which
they seldom are). Or you may find an ee or ef pad or shoe STILL
outperforms an ff in the real world.


I'm gonna have to reluctantly agree with you, yet again.
I don't ever dispute fact.

There is a lot more involved in brake performance - particularly hot
performance, than simple coefficent of friction.


It must be the case that friction isn't a *primary* determinant of brake
performance, hard a pill as that is to swallow.

In this case, the test using a one square inch sample of pad material
TOTALLY misses the mark - meaning the test design is faulty from the
start.


You'd think the SAE would know how to design a friction test though...

And as for not using EE friction materials - SOME of the cruisers
used in thase testa use ef or ff material in the
persuit special" vehicles, while civilian and even taxi (heavy duty)
use may have EE from the factory.


I know. I know. You don't have to rub it in.
I apologize for chastening you for using EE pads and shoes.

I still think my Toyota OEM shoes are FF so I'm gonna get FF.
Can you summarize again the short list of brands you'd recommend?
I want to do the work for the owner this weekend.

Thanks.