Brake pad edge codes

[Q45tech]

"The Chase Test, better known as the SAE J866A test procedure, provides a uniform means of identification that may be used to describe the initial frictional characteristic of any brake lining.

The Chase Test is used to assign a two character code (e.g. EE, FF, GG, HH, etc) to a specific friction formulation. These characters represent the coefficient of friction when a 1" square piece of friction material is subjected to varying conditions of load, temperature, pressure and rubbing speed on a test apparatus known as the Chase machine.

The coefficient of friction measured by the Chase test describes the relationship between the two forces acting on the friction material. A clamping force is exerted on the friction material, resulting in a frictional or resistance force. A low coefficient of friction means that very little of the clamping force is transferred into resistance force. On the other hand, a high coefficient of friction means that given the same level of clamping force, a higher resistance force is generated by the brake pad.

For example, a pad that carries an HH code has a normal coefficient of friction of 0.55 or higher, and a hot coefficient of friction of 0.55 or higher.

The first letter of the code represents the normal friction coefficient. This is defined as the the average of four test data points measured at 200, 250, 300 and 400 degrees Farenheit.

The second letter of the code represents the hot friction coefficient based on a fade and recovery test. We all should know what brake fade is. If you've ever had to use the front brake extensively and found that its effectiveness quickly diminished, that's fade. Recovery is basically the period where the brakes are gradually cooling off.

The hot friction coefficient is defined as the average of 10 data points located at 400 and 300F. on the first recovery cycle of the pad; 450, 500, 550, 600 and 650F. on the second fade cycle; and 500, 400, and 300F on the second recovery cycle.

The range of friction coefficients assigned to each code letter are as follows: C = less than 0.15. D= 0.15 to 0.25. E= 0.25 to 0.35. F= 0.35 to 0.45. G= 0.45 to 0.55, and H= over 0.55."

Theproblem is the test never assumes a pad will get hotter than 650F and it still only measures the 400-300F range roughly what a single 70 mph stop generates.

[Eswift]

another big problem is presented with the permissible range of a specific edge code, say GH.

2 samples with the same code could be as follows:sample 1 : normal uF: 0.45 and hot uF: 0.551sample 2: normal uF: 0.549 and hot uF: anything above 0.55!

you can see that even though these samples have the same edge code, their characteristics barely overlap, sample 1 providing much reduced frictional coefficient in all conditions.

i wonder how widespread procedure SAE J-1652 is now adopted....(uses disc brake pad size/shaped test blocks instead of a 1 inch square)

for those of us more visually inclined...

check outhttp://www.ifriction.com/reports100.htm

q45 tech: any idea where the RWD infiniti cars fall in this spectrum?

[Q45tech]

The Q pad composition has varied since 1990 becoming less agressive as owners complained about early dust and the fast wear of pads. FE but now FF...........I can remember at least 4 different colors and looks of material in the front pads.the pads ended in U90, U91, U93.I have been using the Metal Master since 1997 on my 3rd set in 140,000 miles.

[Eswift]

i recently put the metal masters on all four corners as well, they seem to be gripping like champs.

[911/Q45]

I've had friends complain of excessive rotor wear with Metal Masters, what's your experience?

[Q45tech]

Depends on the word excessive. 40,000 miles is good to me but I retrue them every 6,000-7,500 miles or so. Therefore I create most [little more than half] of the wear..004" x 6= 0.024" out 0.040" possible

The pads are less expensive than the rotors but ideally you would want then to wear out at EXACTLY the same time from a labor stand point or just change the pad even if slightly more than half worn when the rotors are at minimum spec.

The pads are 7mm thick the rotors have only 1 mm per side of wearable margin obviously the number and length of use varies by driver and location.......some get 15k [women real estate agents] some get 40k [salesmen on interstate] with exactly the same pad/rotor on the identical car.

Excessive rotor reaction is probably from the fact that at 600-700F the MM pads may still work better than oem so instead of fade you just drive harder.............fade is usually built in to oem to avoid you destroying things - boiling the Dot 3 brake fluid which will leave you no brakes......fade means back off.

There is always a downside to every modification no matter how minor or simple. Just like performance summer tires, better high temp pads are more dangerous in cold weather....at least the brake pad can be warmed up by application but the tires cannot below 30F!

[Eswift]

americans need to accept the fact that brake systems, just like tires, require an increased replacement rate when the car is driven hard or when higher-performing comonents are used. (these things tend to go hand in hand, suprisingly enough) (in this case, more agressive pads, or lower profile tires...)

[greg_atlanta]

G35 owners have been whining about excessive brake dust (obviously soft pads). I guess they'll switch over to harder pads and just chew their rotors up faster!

:pface