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Brake Terminology, Technical and Trends

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Brake Terminology, Technical and Trends

Hi Guy's,

I have a favourite saying "No matter how much you polish a turd, its still a turd".

I've been away from the brake industry for a while but some things never change. The polishing of products to convince people to buy. I thought it might be a good idea to share some technical terms and some of the science behind brakes so you can compare apples for apples as they truely are behind the glossy marketing and verbal diarrhea. 

I have no intention of naming or bagging out any brands or manufacturers (unless they piss me off) so lets keep it clean and educational.

Brake Pads

I’ve been fortunate enough to have been factory trained with a couple of friction lining manufacturers around the world. NAO, Sintered metal, carbon metallic and low metal high carbon pads. 

One thing is for sure, its personal. Every driver has a different perception of what is good braking. Why we have so many arguments ;-)

The most basic of identifiers for brake lining characteristics is the good old SAE J661 hot and normal (cold) friction coefficient test which is the codes stamped on the pad backing plate. They will look like; EF, FF, GF, GG etc printed in between a whole heap of numbers. The other numbers refer to batch codes and friction formula used. The USA and Europe require this detail to be marked on the pads to comply to various legislations.


SAE J661 - Friction identifiers.

Normal Friction , Hot Friction   is the order of the codes

E = 0.25 to 0.35 mu

F = 0.35 to 0.45 mu

G = 0.45 to 0.55 mu

H = 0.55 and above 


The USA (mainly Ca and Wa) have introduced a hazardous materials legislation called Chapter 70.285 RCW which I have had the joy of participating in for compliance. They've identified a number of ingredients in brake linings that are polluting water ways and making their fish glow in the dark. Copper reductions is a major topic in the USA as this is one of the main offenders. As with the bans on asbestos many years ago, the same appears to be happening with Copper. 

Another topic is the European R90 compliance. Its been around for a long while but is gaining more focus locally. Possibly because sales guys have run out of things to talk about. R90 is all about driving comfort. NHV (Noise, Vibration, Harshness) is the focus. This is directed towards regular road pads of which most OEM's are compliant and aftermarket no so much. 


Key metrics for measuring performance; I'll add some more detail about these soon.

Torque response  (initial bite)

Peak effectiveness (peak friction @ time/temp/pressure)

Release speed (speed to fully retract)

Modulation factor (compressibility and a combo of above)

Pad wear 


A good driver will understand these metrics and will be able to adjust his methods to suit in order to achieve the desired outcome whether it be sprints, endurance, off road, or just regular road driving.

I hope this terminology helps.

Please feel free to ask any questions. No such thing as a dumb question.




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It's not a legal requirement in Australia to conduct the J661 test or print on the backing plates.......yet. There is little legislation in Australia to control the after market.

I suggest you ask the reseller for the hot and cold friction coefficients and see if he chokes.

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So why is normal and hot friction characteristics important?

Depending on the material elements used in a compound the friction lining will behave differently at different temperatures. This has many positives when deciding on a material that best suits the application and driving style. Torque Response or Initial bite is one of the key characteristics considered at low temperatures. If your starting an event or routine and your brake temperature is low (approx 100 C) then the friction level most likely will be different to when the brake temp is 200, 300, 400, 500, etc. The SAE J2522 or AK Master dyno test has a routine to collect this data when developing a product. 

I've attached an example chart of some random test data off a dyno. The initial torque response is clear to see and so is the peak effectiveness. So if I wanted to run for lead position at the first corner with cold brakes (100 C) and stabilise at 0.5 mu to achieve good modulation I'd probably lean towards the red compound. If I had warmed up to 250 C then I may go for the black compound. If I were in a lighter car or going argy bargy then the blue or yellow may be the better choice. 

Choosing a compound based on max friction is not as simple as most egberts make it out to be nor is it the best option in many applications. Too much friction at the wrong time can flat spot tyres or put you on the grass (hopefully), initiate ABS modulation which governs braking performance or too little affects confidence and competitiveness. 


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