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Brake Pads and SAE J866

scrllock

Autocross Champion
Location
MI
You either didn't read the article or understand SAE standardized testing and DOT compliant regulations. The higher a brake pads coefficient of friction, the greater the stopping power (all things being equal) Full stop.
He's half right. As you've noted, there is a standard process for evaluating the coefficient of friction. But if you're over-braked for the tire, or under-braked for the weight, higher mu doesn't equate to greater stopping power.
 

victorofhavoc

Autocross Champion
Location
Kansas City
He's half right. As you've noted, there is a standard process for evaluating the coefficient of friction. But if you're over-braked for the tire, or under-braked for the weight, higher mu doesn't equate to greater stopping power.
Yes, the same kind of standard process that DOT enforces on treadwear ratings and grip...

You can have two tires with 200tw that wear totally unlike one another, but you can expect them both to be less durable than a 400tw. Not to mention dot rating for grip states that a Hoosier R7 has less grip than any 200tw tire... Because that's what it is when the tire is cold for their test specs.

Theres a reason that brake manufacturers don't publish heat vs mu charts with good detail frequently. It's also up to them to do the testing, so while the process can be somewhat standard the results will never be directly comparable between brands or even years of manufacturing. The tolerance for reporting is also massive. One manufacturer could rate their pad at 200F and 400F while another rates at 300 and 600...and if neither one tested for 800F where will the dynamic mu value be and how will the bonding agent react when you're in a panic stop or doing some light track duty?

Unless I missed something in the article and there is actually a standard testing procedure and a lab that DOT runs where they actually sample pads against a standardized iron surface and in the same conditions independently from the manufacturers... Happy to be wrong here, but I don't believe this is the case.
 

victorofhavoc

Autocross Champion
Location
Kansas City
I was curious, so I looked up the actual sae j866 spec, which only defines how to mark the pads with averages across 4 data points, and pretty much nothing else. But keep in mind sae specifically calls out that these codes are just a sample point and should not be used as a strict guideline for purchasing or using pads. Official j866 is attached...

It does references j661 standard testing procedure, which is a cylindrical drum testing approach at specific rpm. There is no DOT testing procedure behind this and no standardized assessment I've found. It's a self reported thing by manufacturers and again depends on the specific instrument they use to test with... A quick search finds that several companies make the testing drum to use, and on the low end they run about $30k for cheaper Chinese ones, so nothing standard there.

I stand by my statement... The codes can be useful for comparing pads within a manufacturer's range for a given release period (like when they're using the same machine for testing all the related pads), but not for cross manufacturer or longer term comparison...
 

Attachments

  • SAE J866_201203 Friction Coefficient Identification and Environmental Marking System for Brake...pdf
    6.2 MB · Views: 39

scrllock

Autocross Champion
Location
MI
Theres a reason that brake manufacturers don't publish heat vs mu charts with good detail frequently. It's also up to them to do the testing, so while the process can be somewhat standard the results will never be directly comparable between brands

Sure, TRW, Textar, etc. don't, but they're selling you street pads that might never exceed 400F. Most track pads I've seen come with heat vs mu charts. Pagid, Ferodo, PFC, Hawk, Raybestos, Race Technologies (Brembo), even iSweep provide this. If you're looking at track tires and pads, no shit DOT ratings aren't going to be useful. In OP's case, I doubt he's concerned about road grip with R7s or friction at 1400F.
 

victorofhavoc

Autocross Champion
Location
Kansas City
Sure, TRW, Textar, etc. don't, but they're selling you street pads that might never exceed 400F. Most track pads I've seen come with heat vs mu charts. Pagid, Ferodo, PFC, Hawk, Raybestos, Race Technologies (Brembo), even iSweep provide this. If you're looking at track tires and pads, no shit DOT ratings aren't going to be useful. In OP's case, I doubt he's concerned about road grip with R7s or friction at 1400F.
The charts they do provide are not exactly what I would call "accurate". Those are more marketing tools than anything. Again though, you can't compare a hawk diagram to a ferodo diagram. Just because the coefficient of friction is a standardized metric does not mean that testing process is going to be equal in two separate circumstances and that data is comparable. It's like comparing track times for different days with different drivers. Sure they're all measured in minutes and seconds and those are standard units, but that doesn't mean they're comparable.

Yes OP is looking at street stuff, and no dot is not intended for track oriented things, but my point was that the dot rating exists for them still and because the test isn't designed for the use spec the results are not valuable for someone looking to use them outside of the testing spec capacity. Pretty much anyone with a "sporty" car will hit 600F+ on the street at some point. Think long hill descent and some hard braking at the end, and you're quickly pushing high heat where most pads will glaze.

Also, there's this note at the very top of the j866 spec:

"NOTE: It is emphasized that this document does not establish friction requirements for brake linings, nor does it designate significant characteristics of brake linings which must be considered in overall brake performance. Due to other factors that include brake system design and operating environment, the friction codes obtained from this document cannot reliably be used to predict brake system performance."
 

DerHase

Autocross Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
If you really want to get an idea of how different pads will react as far as friction coefficients and "feel" goes... flash your car with Simos Tools to enable the high speed logging. Then do a bunch of driving with different pads, logging longitudinal acceleration vs brake pressure.


Ferodo DS2500s:
1694396038234.png


Ferodo DS3.12s:
1694396157381.png


The DS2500 is from a bunch of repeated hard stops on the street (like 20 of them), the DS3.12 is from on track, but you get the idea of what I'm trying to show. Doing more careful testing on the street with slower threshold braking would be the way to tell. Super high g-forces won't be comparable in the above samples, but some of the lower G stuff should be pretty accurate. The 3.12s have a ton of initial bite.

I forgot to follow up to my original reply a while back on page 1... the DS3.12s do not appear to have any friction codes on them anywhere that I could find (I looked for them when I put a brand new set on earlier this year, just forgot to follow up with this thread).

I can say that the DS3.12s are good to at least 1470F though with no real significant change in feel... if anything they get more grabby at elevated temps:
1694396565669.png
 
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echelonphoto

Ready to race!
Location
northeast
Reviving this thread. I just need a decent set of street pads and rotors....not looking to race and would be happy with oem as they have lasted me 40 k miles and still stop great.
 

GolfRRRR1

Go Kart Champion
Location
Michigan
Reviving this thread. I just need a decent set of street pads and rotors....not looking to race and would be happy with oem as they have lasted me 40 k miles and still stop great.
Just read the 1st post on this thread, your answers are there. Unfortunately the thread went off course pretty quickly when others brought in the discussion of race pads/tires and temps you should never see on the street. All things being equal, the 1st post should be a good general guide for STREET pads and offer up a coefficient of friction rating among competitive products as close as you can get unless you want to do an exorbitant amount of independent testing on your own. It's a guide and should get you closer to what you are looking for.
Good luck.
 

Drewpul

New member
Location
Glen Ellyn, IL
Car(s)
Golf Sportwagen TDI
Ficton rating...haha! Totally glossed over that.

Yeah, I couldn't find anything online about this brand. I did email idparts to inquire on more information. I'm assuming it's probably some house brand made in China?
 

Drewpul

New member
Location
Glen Ellyn, IL
Car(s)
Golf Sportwagen TDI
I head back from ID Parts. They confirmed Halten is their house brand and the pads are made in Taiwan.

I asked them about durability: "Going with a Brembo or Bosch I know will be durable. Are you able to share if this manufactuer manufactuers other brands that I may recognize?"

And he replied with "They manufacturer many brands that you know and have mentioned but we are not allowed to confirm what brands exactly."

So as long as he is being truthful (and idParts is a reputable company for diesel vehicles), if I'm interpreting this right, the same manufacturer also creates Brembo or Bosch pads. Now that does NOT mean they use the same techquines for production, nor that the compund is the same (likely not). But it gives me at least a bit of confidence that this manufacturer has the ability to make quality pads.
 

GolfRRRR1

Go Kart Champion
Location
Michigan
I head back from ID Parts. They confirmed Halten is their house brand and the pads are made in Taiwan.

I asked them about durability: "Going with a Brembo or Bosch I know will be durable. Are you able to share if this manufactuer manufactuers other brands that I may recognize?"

And he replied with "They manufacturer many brands that you know and have mentioned but we are not allowed to confirm what brands exactly."

So as long as he is being truthful (and idParts is a reputable company for diesel vehicles), if I'm interpreting this right, the same manufacturer also creates Brembo or Bosch pads. Now that does NOT mean they use the same techquines for production, nor that the compund is the same (likely not). But it gives me at least a bit of confidence that this manufacturer has the ability to make quality pads.
I bought a set of brake rotors and pads from IDParts (their pads) for my wife's Passat TDI and she made me take them off (not enough bite) and buy the TRW stock pads. I'm trying to work with my wife about how she drives but it's futile, she's either full throttle or full brake.....I guess that's not too bad LOL.
 
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