Whats the stupid fixation with the coefficient of friction anyway?
As any fule kno, friction is notionally independent of contact area, and force due to friction is determined by the coefficient of friction *and the applied force* so if you want more frictional force, you just need to press the pedal harder, or have more servo assistance.
Simply ignoring all of the other (engineering) considerations which have been cited, relating to brake performance in the real world, will not help you be enlightened about anything. It just makes you look like a dumb f*ck trying to be cleverer than your brain permits.
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.
Mostly stopping distance
Mostly pedal pressure
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.
There are presumably 2nd order differences in pad performance, but we've no idea what they are. EE versus FF is not it seems the relevant criterion as long as the car can apply enough force to lock wheels with the pads. Wheth er all modern cars can do that with EE or not I also have no idea. FWIW cer tainly all historic ones can't.
you're getting a bit, but afaik none of us are brake specialists or researc hers.
There's something happening here But what it is ain't exactly clear There's a man with a gun over there Telling me I got to beware
I think it's time we stop Children, what's that sound? Everybody look - what's going down?
There's battle lines being drawn Nobody's right if everybody's wrong Young people speaking their minds Getting so much resistance from behind
It's time we stop Hey, what's that sound? Everybody look - what's going down?
What a field day for the heat A thousand people in the street Singing songs and carrying signs Mostly saying, "hooray for our side"
It's time we stop Hey, what's that sound? Everybody look - what's going down?
Paranoia strikes deep Into your life it will creep It starts when you're always afraid Step out of line, the men come and take you away
We better stop Hey, what's that sound? Everybody look - what's going down?
We better stop Hey, what's that sound? Everybody look - what's going down?
We better stop Now, what's that sound? Everybody look - what's going down?
We better stop Children, what's that sound? Everybody look - what's going down?
Stephen Stills
Guys and gals:
a) There are many thousands of mechanics out there who _REALLY DO_ have the best interests of their customers at heart. b) Many of them are perfectly willing to share their experiences with their customers. c) And, for the most part, they are willing to share sources and reasons fo r them. d) OEM parts, for the most part (pun intended) will do the job nicely. I ju st replaced the rear brakes on my 2014 Ford C-Max Energi at 67,000 miles - the front brakes are still at 70%. I used 100% OEM parts, at a material cos t of $180, retail-from-Ford. NOTE: As this is a plug-in hybrid, dynamic bra king, if exploited properly, does most of the actual work involved. Saving the brakes.
Deep analysis is not required. Attention to life-safety *IS* required. And that is ALL that is required.
Understanding brakes 101:
The primary job of brakes is stopping the vehicle in a controlled, safe, re liable fashion. Whatever wearing parts as are necessary to complete this task are sacrifici al to the primary job. Manufacturers have absolutely no interest whatsoever in compromising this s ystem at any level and in any way. Too many Lawyers out there for them to t ake such an absurd risk.
Kinda-sorta makes debates on the number of angels residing on the head of a ny given pin, whether dancing, or not, patently absurd. FULL STOP.
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.
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.
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)
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*
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