Need help INTERPRETING these test results police cruiser SAE J866a Chase Test

Thanks for that observation as I'm trying to derive as much real-world benefit from the police cruiser report as is possible given Clare's astute observations about EE and FF pads faring differently, but not because of their coefficient of friction.

There were 3 police tests over the decade, where only the penultimate test aimed for uniform pedal pressure.

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The middle test is the one that aimed for a given pedal pressure: a. 45-to-15mph at 10ft/s/s (approximately ~10 foot pounds +- a few) b. 70-to-30mph at 22ft/s/s (approximately ~20 foot pounds +- a few) c. 90-to-0mph at 22ft/s/s (approximately ~30 foot pounds +- a few)

Fundamentally, they said pedal pressure is, effectively, what a human does all day every day - hence pedal pressure is, arguably, more important in a well-used "cruising" vehicle that doesn't do panic stops consistently.

A targeted deceleration rate where pedal force is proportional to pad temp.

The other two studies were different.

1. Mostly stopping distance
2. Mostly pedal pressure
3. Mostly driver perception

In the end, the DOT edge code (AMECA edge code) is only slightly useful to a consumer, I think. I wish it were more useful, but I've gleaned out of it what I can, and that's the best any of us can hope to do.

I was hoping to get more insight from the scientific and mechanical folks here.

Ain't gonna happen. The people what know how this shit works aren't going to waste their time arguing with your preconceived misconceptions.

It's a valid question of who cares about choosing the proper brake pads.

Bear in mind that the Toyota FF pads are $157 a set at the local dealership, while at a local parts store, I can get FF pads for $20 a set.

C = Up to 0.15u E = 0.15u to 0.25u E = 0.25u to 0.35u F = 0.35u to 0.45u G = 0.45u to 0.55u H = 0.55u to 0.65u Z = Unclassified

That's a huge difference in price, for material that has the same friction coefficient, if not quality, don't you think?

So it behooves intelligent people to figure out, scientifically, whether there is a way to tell what's *different* about those pads.

Everyone understands a number line, but there are non-linear issues here which nobody here seems (so far) to understand such that they can tell us how to properly compare the two brake pads based on the information a consumer would have.

In the end, I don't see any indication whatsoever that anyone here knows how to properly compare the performance of those $157 and $20 brake pads and shoes in order to make an intelligent buying decision.

That's kind of a sad revelation for this newsgroup, don't you think?

Not at all. Even a "brake engineer" would not be able to tell ypou how to tell the good fromthe bad (or less good - don't knowthere is any "bad"brakes on the market - even a lot of the "counterfeit" stuff will stop the car). The "brake engineer" would likely beable to tell you which of "his" product is better - but not necessarily if his was betteror worse than another brand.

Back when I was a Toyota tech and service manager there were at least

2 different formulationsof brake pad that fit numerous Toyota vehicles of the time - one was used up to a particular production date, and another after. Both were available as replacement parts, and I always used the one, regardless of vehicle production date, because it stopped better and I could install the second and third set without having to replace rotors. It was a difference between the metal used in the "semi metallic" lining. One was magnetic - the other had brass in it. The brass stopped better and didn't cause pitting of the rotors. The pads didn't last as long, but virtually nobody ever actually wore out the "magnetic" ones before the rotors needed replacing, so the pad life, in and of itself, was a total non-issue. IIRC the brass was the early pad and the iron was the replacement/update.

The same situation rose years back on, I believe, FORD brake shoes where the linings would deteriorate and fall apart before the half wear point. They went from rivetted to bonded, and then the glue started letting go, and the entire lining would free-wheel between the shoes and the drum. It was a real bugger if that happened only on one front wheel. It would have a MONSTEWROUS pull one time, then brake fine the next - and you NEVER knew when it was going to pull - or which way - because sometimes the loose material would grab, sometimes it would hold properly, andothertimes it would do virtually nothing -

- -

Brake materials are a fine line between a science and a "black art"

That's why I say those who say "you get what you pay for" are misguided because a $157 pad "might" be just as good or bad as a $20 pad, where I can prove this statement for the $300 20W Panasonic speakers in a Toyota since I know the specs on the $50 speakers at Crutchfields.

Even at Crutchfields, you can get a good $50 speaker or a less-good $50 speaker, and the price is exactly the same.

So if someone tells me "you get what you pay for", they'll get the same rant from me that everyone loves to pick products off a number line, but the real number line is a bunch of specs, and not a simple price.

That's retail for you! :)

I think price is not an indication of anything other than what the marketing can make people pay. It's certainly not an indication of quality.

I'm not sure what you mean by "scrapyards". To me, that means a junk yard, which contains dead cars. I wouldn't buy brakes off a dead car for a billion reasons which are obvious so I shouldn't need to state it.

What's the difference between my concept of a junkyard (which contains entire cars that were thrown away) and your scrapyard?

Are you talking about *used* brake pads or *new* brake pads?

There is no other logical conclusion to be made, given the information we have. Price is NOT the determinant of a good or bad brake pad.

The sad thing is that there is no determinant we can make that will hold true other than there is no difference practically that you can do anything about.

I'm NOT saying they are all the same. I'm saying we consumers can't tell by having two of them in our hand or having two of them sold online.

Or rubber in bicycle brakes.

I think you hit the reluctant nail on the head!

The only way this can make sense is if all brake pads work. Period.

Because if people were getting into accidents due to bad brake pads, someone would step in and stop that (we hope).

Notice even the police report, which is the only scientific study we have, never said any pad was better or worse - they just required more foot pounds or fewer foot pounds of pedal force for the same deceleration value.

They never said anything about not being able to decelerate at the desired deceleration value.

So, I very belatedly am getting the lesson that, in terms of stopping a typical passenger vehicle, all pads sold are just about the same in terms of performance.

Another way of saying that is that no matter what the price is, you can't get a bad pad (nor a good pad). All you get is a pad.

All this assumes that you can't afford to run your own scientific tests, because the one scientific test we do have, concludes as much anyway in that there's no way to tell unless you run the test yourself, which you can't do.

For actual racing, those guys can spend the actual immense time comparing two different pads, but the consumer is left to realize, as sad as this conclusion is for me to state, that all consumer-available brake pads are pretty much exactly the same in terms of stopping ability.

Sigh. It's sad. I didn't want to conclude that. I really didn't. But it is what the science tells us it is. The rest is just marketing bullshit and fear mongering from the butt-dynos that think if they paid $157 for a pad, then it must be better than if they paid $20 for the same pad.

I agree with you that the primary role of friction material is their friction, but as the AMECA engineer told me, the way they outgas alone can have an effect that is huge, as you are also noting.

It would be nice to figure out what these second-order effects are, such as outgassing as mentioned by the AMECA engineer, as the police cruiser test already eliminated any second-order effects from a difference in vehicles since they tested the different pads on the exact same vehicle.

So we can tentatively state that you are 100% correct that second-order effects (outgassing) apparently are as big as first-order effects (friction).

The AMECA engineer said that all materials heat up differently, which, he said, also effects the performance of the pads.

So I think we have two potentially high second-order effects which are (shockingly) almost as important as the first-order effect of friction coefficient:

1) outgassing (outgasing sp?) 2) heating 3) ?

What other potentially very high (as high as friction) second-order effects could we have, when we've eliminated the difference in vehicles and driver?

Pad vibration - which has an effect on gas venting, counterd by the effect of reduced pad contact

May not be a HUGE difference, but it is possibly a factor. Also heat CONDUCTANCE - metallic pads conduct more heat to the caliper than ceramice - making the boiling point of the fluid more critical (if running metallic or semi-metalic pads you want to be sure to be running DOT4, not DOT3, and you want it freash and dry) One reason Chrysler was using composite pistons for several years in the early no-asbestos days (until they found the pistons swelled and stuck - - - )

The tests were limited - addressing the use a cruiser puts the brakes to. If you know how to read the information, it tells you a LOT about the brakes - but you are correct - there is no "best" brake material - it depends onthe use they are being put to, and what YOU want from them. There may well , however, be " WORST" brakes.

If brakes require higher pedal pressure to stop in a longer distance (and decellerate at a lower rate) both when cold and at normal temperature, and fade significantly on the second and third application - they are pretty crappy brakes.

If they require low pedal pressure to decellerate quickly to a stop in a short distance when both cold and at normaltemperatures, AND do not fade appreciably on the second and third (panic) stop - they are pretty darn good brakes - anlness they squeal like a stuck pig, only last for a month of driving, and/or destroy brake rotors - and/or coat the wheels with nasty corrosive brake dust - - -

No, not at all - you are TOTALLY missing the point. The different brake PAD materials are mission specific. A ceramic pad will outstop a economy organic pad when hot - hands down. Every time. A metallic pad will usually stop better after several panic stops, or when towing a heavy trailer down a longhill - than either the organic or the ceramic. Both the semi metallic and the organic will stop better on a cold stop than a ceramic.

No. a $85 Thermoquiet Ceramic will stop better than a $20 no-name organic pad - and you can be pretty well assured you will not get a $20 ceramic pad unless Rock Auto has something on clearout.

Price is not a sure predictor of quality - but can be a pretty darn good indicator.

Also, a high iron semi metallic WILL wear out your rotors faster than either the organic or the ceramic unless the organic causes the rotor to blister because of uneven pad material transfer, and abuse.

What you TOTALLY do NOT understand is how disc brakes, in particular, work - and how the co-efficient of friction changes.

When you "bed in" pads, you are burnishiung a thin coating of pad material into the finish of the rotor.. The stopping power of the brake depends on the co-efficient of friction between this burnished in friction material and the pad - not between the pad and bare metal. How this coating is applied, and maintained, dictated the braking charachteristics of a disc brake as much as anything. If you stop hard and fast and keep your foot onthe pedal at a stop untill the brake cooles,there will be a heavier deposit on the rotor at that point - UNLESS the padmaterial deposited on the rotor does not adhere properly and it pulls away with the pad. Either way you will end up with uneven braking - either a "thump" or a "skip" on the next brake application.

A "quality": pad will transfer evenly and bond reliably to the rotor during the perscribed "bed-in" and will not cause uneven transfer under "normal" driving conditions. It will also not cause or promote corrosion between that pad mnaterial and the rotor steel (which causes "scabbies" and pitted rotors (often mistaken for the less common, but sometimes "real" "warped rotor".

Inferior brake friction material performs more poorly in these ways than premium materials.

A worn, glazed, or grooved rotor will not "bed in" reliably because the surface will heat and cool unevenly - with uneven pressure across the brake surface -

So brake friction material quality AND the installation affect brake performance.

Also, the brake mounting hardware - the shims and springs either provided with the new pads, purchased separately, or salvaged from the prior installation (whether OEM or aftermarket or totally missing) alsohave effects on the performance (and life) of the brakes. Heat transfer, Vibration, and freedon to move in the caliper, are all effected by the quality and presence of the proper mounting hardware - which is designed/modified by the pad manufacturer to matvch the characteristics and requirements of their particular pad and friction material - which is why "premium"brake kits are supplied with the proper hardware to install the brakes for their best performance.

More paranoid bullshit.

Total bullshit. The friction rating doesn't tell you much, but the difference in required pedal pressure, and the difference in stopping distance - notto mention the difference in pad temperature between the best and worst in the test is VERY significant. What is NOT significant is the predictabiklity of the results based on the frictionrating of the pads under test. (almost totally useless)

WRONG. And do your friend a favour and send them to a REAL mechanic to have their brake work done. I fear you are DANGEROUS.

You still have not learned ANYTHING?????

The specs on speakers are known to be some of the best fiction ever written, followed only by the specs on consumer stereo equipment.

You "only" get what you pay for - and then only if you are both lucky and astute. You SELDOM get more than what you pay for

You can take THAT to the bank.

Because someone was unloading something they didn't need, at a price to get it off their shelves - and your requirements were not severe enough to require anything better.

I've also been "lucky" enough to pick up some real "bargoons" by being at the right place at the right time. I often buy what no-one wants any more - nobody inOntario wanted a 1972 Pontiac Firenza in

1974 or 1975 - so I gor an almost pristine Vauxhaul Viva HC Magnum coupe for $75 - and it served me well for a number of years before I sold it to a friend of my wife, who needed a car and had no money for something "good" - and she drove it another 7 years untill it required a part that was not readily available or available at a decent cost .

I got "more than my money's worth" - I got "more than I paid for".

The same with my current pickup truck which I bought for $1500 because nobody wanted a meticulously maintained 16 year old ford Ranger with over 300,000km on it. It's been virtually trouble free for 6 years - I've spent about $1500 on repairs over more than 50,000km, and all indications areI'll get a few more years out of it. I got more than my money's worth.

In both cases It was because I new the "value" of what I was buying better than both the seller and other potential buyers.

You are FAR more likely to get less than you paid for - particularly when buying any commodity new at retail - where you are SIGNIFICANTLY less likely to get more than you pay for.

Price is not an accurate predictor of quality, but with a few other often obvious clues, it is a pretty reliable indicator.

It is, as I have stated, an indicator, but not a predictor or guarantee of quality.

No they are not - and in MANY places it is illegal to sell used brake parts and used exhaust/emission parts.

Sometimes a car ends up in a scrapyard with lots of brand new parts on it. The owner puts $3000 into making it safe to drive - new brakes, suspension,and tires - the either has it hit, or blows a motor or transmission, and decides not to keep it and repair it - or they spend all kinds of money fixing it up - making it into their ":boy racer's wet dream" and then cannot get it to pass smog - and it ends up in the scrapyard with LOTS of good and/or expensive parts on it.

That said - as a matter of principal - unless no other adequate source of brake parts was available, I'd be looking elsewhere - first. Have I used "used" brake parts in the past?? Yes. I put a complete used rear axle from a '63 Belvedere into my '53 Coronet - brakes and all - as an upgrade when the originals failed and OEM parts were not readilly available, and the old design was less than optimal. ANd I put used parts on my '49 VW in Livingstone Zambia. Where was I going to get new parts??????? On a Sunday afternoon half way between Choima and Macha - (look it up on Google Earth - and keep in mind this was 44 years ago - - - - .

Not necessarilly.

Perhaps not of a good one, but quite often of an inferior one

again, bushels of bovine excrement.

And why do you, like so many "millenials" (I'm aking an assumption here from significant evidence) INSIST on buying everything on-line????

Obviously not sufficientfor a 3 ton vehicle going 100MPH - and definitely not as good after a long downhill stop - -- but likely, at low speeds - al ot better than you suspect!!!

There is SIGNIFICANT difference between different compounds of "rubber" pads for rim brakes - includingin their stopping power and their destructive effect on rims - some better for chromed rims, and others for Alloy rims - some working better for side-pull, and others for center pull (different amounts of pressure available)

I just picked up a VW door latch assembly on eBay. It's a large electromech anical component that fails frequently. The new part was probably made in C hina but I suppose it could be made in some European shithole country. It l ooks solid enough and I can't imagine that it could possibly be more unreli able than a genuine VW part - whatever the heck that means. It cost me $23, including shipping. I just saved $130.

More of "all you ever wanted to know about friction materials" but were afraid to ask - - -

and

and

and

and

and

a whole lot more!!!!!!!!!!!

And here is some more real good information on brake pad materials - on a lower level - for the non-engineers out there.

Clare Snyder posted for all of us...

They used to be a bitch to get out.

To Madman: When I was early in emergency services I used to run my private vehicle. I had to pay attention to braking because after 3 stops there were NO brakes. I got the police shoes because I was all into it. What a difference! When I got a pursuit certified vehicle it was wonderful. They are designed and built to endure punishment. Try and go to the dealer and get the model, good luck with that. Watch what happens on one of the police shows. See which car is destroyed or smoking at the end. The actors can't make the corner because they got no brakes. Or the engine expires. Something is to be said when one goes from 0 to 40 then 40 to 0 repeatedly and sit there idling for the next 1/2 hour then going to the next call. Then there were the ambulances and fire trucks. *Training*

Exactly. You've been right all along while I was hoping beyond hope that there is an intelligent way to select a good/better/best brake pad.

You were right. I was wrong.

If you have two pads in your hands, or two on the net, you can't make an intelligent choice between them, other than to know if they're the same or not, and to know who made them, and to know what their cold and hot friction coefficients are.

That's it.

Each pad can be different - but you have no way of knowing that from the pad itself.

Nobody complained about fade in that one report we have, did they? I don't think we have any better "fade" test than the Chase value for hot friction (which was E or F depending on the pads tested).

So, while fade is important - it's a useless criteria since we have no way of knowing the fade.

It's just silly to bring up all the things that *can* happen if you have no way of choosing between them when the pads are in your very hands.

I don't disagree with you that two pads can be vastly different, but you have no way of knowing anything other than their tested friction, their manufacturer, and whether two pads are exactly the same material.

That's all you've got since brands are almost meaningless (e.g., PBR, Axxis and Metalmasters are the same company) and semi-metallic/metalic/ceramic marketing is even more meaningless.

All well and good, but it's like predicting that a baby will become the president of the United States.

Let's just agree to disagree since you don't seem to realize what I know from talking to the Axxis marketing guy that the word 'ceramic' is a bullshit marketing term.

Do you think I don't call these marketing guys up? Do I seem like someone who doesn't ask pointed questions?

Ceramic is complete and total marketing bullshit. The marketing guy told me himself.

(Yes, I see the difficulty of position that puts me in.)

Let's agree to disagree. You believe in marketing. I don't.

I believe in specifications.

Let's agree to disagree.

You think price has some impact on performance. I will prove to you that I can show exact same products with different branding but the exact same price.

Everyone loves a number-line decision, whether it's good/better/best of metallic/semi-metallic/ceramic or $10/$20/$30 or 3-year/4-year-/5-year warranty, but none of that indicates a better or worse object.

Only specifications do, and we just don't know much about the spec other than who made the pad, the code for the exact formulation, and the friction.

Everything else is bullshit.

Price is an indicator of demand only. Demand is influenced by a shitload of factors. You know that. I know that. Let's not argue it. That's what Economics 101 was for, and I already took that and passed it.

If you truly know the "hardness", then of course it matters. But you have no way of knowing the hardness. Do you?

I think I do understand how disc brakes work, but we can discuss what you think I don't understand.

What I know is that your energy of movement has to be converted into something else, most notably heat. Lots and lots of heat.

Yup. Pad deposition. Something about covalent bonds making and breaking under the heat of braking, where the breaking of the bonds elicits heat.

It gets complex HOW the heat is generated (it's not just 'friction'), but the end result is heat. Lots and lots of heat.

The Ameca engineer already explained the burnished pads that the Michegan study used where he said it was to get rid of the volatile gases that come out of the first few heat cycles.

Yup. We all know how to property bed our brakes. I doubt many shops do it though, because it requires a lot of room and a few very hard almost stops where, if there is traffic, it ain't easy to do.

I'll wager that few, if any, shops properly bed the pads. But you'd have that experience because I've never been to a mechanic.

NEVER, and I mean NEVER leave your foot on the pedal after a hard stop! Everyone knows this, so I know you know this. It's the worst thing you can do, unless you love to have judder every few thousand miles as that ped deposition collects more pad over time.

I never understood why, but once a pad print, always a pad print. And it only gets worse.

Unless you re-bed the brakes - which everyone knows - so you're preaching to the choir on even brake pad deposition techniques.

Yes. But. I have no good way of knowing a quality pad from a not quality pad. So it's moot.

It's like me picking out the best students in a class based on whether they wear glasses or not.

It's significant in one thing. Pedal pressure. If pedal pressure is your gig - then it's significant. If pedal pressure isn't your gig, then it's not significant.

The pedal pressure changed about 100%, from roughly less than ten foot pounds to less than twenty foot pounds in the lower-speed tests for example.

What's 10 foot pounds? Dunno when it's pressing on a pedal, but if that's important, then you have to buy a police cruiser and put those pads on it - because it doesn't tell you anything about your car unless it's a police cruiser.

Yup. We agree. There is no useful data other than the AMECA code and even that isn't meant for the consumer.

Knowledge is dangerous. Logic is dangerous. Thinking is dangerous.

Having someone else do all that for you, is dangerous. The mechanic doesn't give a shit about you or your brake pads.

All the mechanic cares about is your money, and getting as much of that as possible, in the least time possible, so he'll skip steps like you can't believe.

I'm on car forums where there are complaints galore about mechanics skipping half the steps in anything because they don't give a shit about anything but money.

The only way to do it right is to do it yourself, is my motto.

You can disagree (and you almost certainly will), but you can't disagree that I'm trying to make an intelligent decision on which brake shoes to buy, and that I probably know them as well as any mechanic who *thinks* he knows them - but he doesn't - because he can't.

Nobody can but the guy who submitted them for their Chase test.

I've never experienced such fade in my life, and I drive a performance car, where I've driven down many a long hill. I don't know why I have never experienced brake fade, but I know it exists. I just have never felt it.

But I've never put in less than FF pads either.

That may or may not be related - we can't tell. It's just a datum.

What's a "police shoe"?

The police report from Michigan tested "regular" shoes only.

If there was a difference, it's hard to tell because nobody (except the police in Michigan it seems) tests *new* pads against *new* pads (after burnishing).

You probably didn't as nobody does.

You probably tested *old* pads against *new* pads, and even if you did test apples to apples, it's not extensible to "my" car or to anyone else's car.

That's the problem with tiny experiments of a single datapoint.

What the heck is a "pursuit certified vehicle"? I drove an EMT vehicle many times. It drove like a truck.

Like any performance vehicle on the road today?

Don't even know what it is. Is it a souped up police cruiser?

That's not a good scientific test.

I have been trained to drive an ambulance. Know what they taught me?

a. Defensive driving b. Noise pollution is bad c. Laws (nobody is allowed to break the law in that state, not even ambulances)

I think in some states emergency vehicles *are* allowed to break the law, but not in that state where I drove the ambulance. Of course, nobody is going to give you a ticket either, but if you kill someone while breaking the law, the onus is on you.

That makes sense that the outgassing of pad A can be vastly different than that of pad B, and, in fact, they "burnished" the pads in the police test to minimize the initial presumed-far-greater effect of that as the adhesives heated up for the first time and vented gases.

Occam's Razor logic tells us that only one of 2 things is happening: a. There is a huge as-yet-unnamed second-order effect, or, b. There is a combination that results in a huge second-order effect.

That there is a huge second-order effect (after friction), there can be no logical doubt.

But what is the 2nd-order effect's cause and can we test for it?

Two Occam's Razor points on that observation above, which is correct.

1. While this vehicle specs DOT3, I'll put in DOT4 instead.
2. Metal versus semi-metallic versus ceramic is marketing bullshit

I know there are no laws that differentiate between metal, ceramic, and semi-metallic - as I've personally spoken to the people who make the Axxis/PBR/Metalmasters pads. They told me it's all bullshit only they said it far more politely and less succinctly than I just did.

Suffice to repeat that a spec of dust makes a pad ceramic, just as a spec of iron makes it semi-metallic.

I posit marketing came up with these wonderful good/better/best number-line decisions for people since people (like Terry Schartz seems to be) want a simple number line instead of those oh-so-very-complex quality specifications.

Where's Jeff Liebermann when you need him!!!!!!!!!!!!!!!!!!!! :)

I get your point, even ensconced inside the sarcasm, so I'll just say it bluntly that I do realize 99.99% of the people out there do not care that they're completely unable to intelligently purchase things using a modicum of logic.

These people all want a "number line" decision, where they can use the good, better, best by "marketing derived" criteria, such as silly words like "ceramic" (where one spec of clay makes it a ceramic) and "semi-metallic" (where one spec of iron makes it metallic).

You're one of those people, most likely (based on Occam's Razor deduction), and that's fine.

You *think* you're intelligently choosing a brake pad, and that's fine too.

You may even buy by one of the three marketing-induced criteria: a. If you're cost conscious, you buy the cheapest FF that fits. b. If you're value conscious, you buy the mid FFs (with a small price bump) c. If you're status conscious, you buy the high FFs (bigger price jump)

I'm not like you. I like to *understand* that which I buy.

That's my take on the main difference between you and me base on the one line you wrote.

I like to make intelligent buying decisions. You apparently don't care to - and that's fine.