View Single Post
  #15   Report Post  
Posted to,,
Clare Snyder Clare Snyder is offline
external usenet poster
Posts: 4,564
Default Need help INTERPRETING these test results police cruiser SAE J866a Chase Test

On Thu, 11 Jan 2018 20:09:25 -0000 (UTC), Mad Roger

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

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)?

Elementary, my dear Watson. There is a HECK of a lot more to brake
pads than just the coefficient of friction - as Ihave been stating
time and time again. Steel on steel is noisy. Steel on steel has no
"feel". Steelon steel makes TERRIBLE brake dust, and steel on steel
would have terrible pad and rotor or shoe and drum life.

The coefficient of friction isn't all that bad - and the difference
between e and f, I would postulate, is not so "appreciable" as
and the difference in fade bertween ee and ff pads is laughable. At
600 degrees an ee can suffer from 0 to 25% fade, while the
"appreciably better" FF suffers from 0-22% fade - which means there is
EVERY possibility that an EE pad would hac WAY less fade than another
FF pad.

The STUPID thing is an fe can suffer 2-44% fade - doesn't make ANY
logical sense, but that's straight from

Friction material consists of a cobination of the following
Fibers, such as fiberglass, kevlar, arimid, stainless steel, and
aluminum maintain the heat stability of the pad. These fibers have
various binding strengths and can be organic or metallic. Friction
Modifiers such as graphite adjust the friction level and fine tune the
performance characteristics of the pad at specific cold and hot
temperatures. Fillers take up dead space in the pad. These are
generally organic materials with some low frictional effect such as
sawdust. Finally, Resins are used to hold the elements of the pad
together so they don't crumble apart.

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

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?

All pads work at least once. The life of the pads is not taken into

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.

Dropping a railway tie into a post hole will stop you faster than a
GG pad will = guaranteed!!!

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

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

Yes, but the assininely simple test procedure is FAR from "real
world". The behavior of a 1 square inchchunk of friction material does
not come CLOSE to the effect of 2 30 square inch arcs of pad material
in a 3 inch wide enclosed drum, or 2 10 square inch pads rubbing on an
open disk - simple things like pad vibration can reduce the EFFECTIVE
friction of a disc pad SIGNIFICANTLY (by cutting the "duty cycle" of
the pad basically in HALF (A vibrating pad is only in full contact
with the rotor roughly half the time)
An off-gassing pad only 1 inch square is not going to "float" on that
gas layer like a 10 square inch patch is under the same pressure. The
"micro-ball-bearings" of brake dust will have virtually no effect on a
1 inch piece of friction material, but may have a SIGNIFICANT effect
on 10 inches of brake shoe (which is why , partly, a grooved pad can
significantly outperform a solid pad.

There are WAY too many contributing factors that have WAY more
influence on brake performance than the relatively SMALL difference
between an e and an f pad. You could have an E pad at .34 and an f at
..36. You tell me there is a quantifiable difference between the
Not in my world - where the rubber hits the road.

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).

Well over half of the "brands" are rebrands - not manufacturers.
particularly the "boutique" brands the enthusiasts and boy racers wet
their pants over

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

VERY limited utility

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.

"Figures don't lie, but liars figure"
You can make math give you any answer you want - ask an accountant.

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

They don't lie, they just, by their very nature, CAN NOT tell the
whole truth
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.


I just want to know WHY?

Because the initial friction co-efficient, as measured by the test in
question, is only one of a miriad factors involved in brake
performance - and a relatively MINOR one in the grand scheme of

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

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.


Well, if I was doing the job, I'd be heading over to my neighbourhood
NAPA store and pickingup a set of their Napa Ultra Premium rear shoe
kits for $57.28 CANADIAN (about $35 US??)and be done with it.
Or possibly over to Canadian Tire for a set of Brembos if they have
them 20% off (they did this week - but their coverage is limited -
they might not have shoes for a 'runner) or Wagners.

Let's face it - they are REAR brakes - and they do less than 30% of
the actual braking. A whole lot less in many cases due to the action
of the load sensing brake proportioning valve that cuts preasure to
the rear brakes when the rear axle us "unloaded" to prevent the rear
brakes from locking and the ABS from activating.

ABB (Brakebond) and Dana are generally predictable performers as