DOT Pad Codes

 This two letter edge code mandated by the DOT, and painted on all street legal brake pads, will give you some indication of their ability to resist fade. But only if you know how to read them. However, because of the wide range involved in each letter, it is only a rough indication.
 

Explanation of D.O.T. Edge Codes Located on all Brake Pads

Official D.O.T. Edge Code

Coefficient of Friction (C.F.)
@ 250 F and @ 600 F

Comments

EE

0.25 to 0.35 both temps

0-25% fade at 600 F possible

FE

0.25 to 0.35 @ 250 F 
0.35 to 0.45 @ 600 F

2% to 44% fade at 600 F possible

FF

0.35 to 0.45 both temps

0-22% fade at 600 F possible

GG

0.45 to 0.55

Very Rare

HH

0.55 to 0.65

Carbon/Carbon only. 
O.K. up to 3000 F where it glows

Notes:    These edge codes are located on the edge of the friction material of every brake pad by government regulation, along with some other codes. The first letter is a grading of the C.F. at 250 F and the second letter is a grading of the material at 600 F. Each letter grade can actually have quite a range of C.F. But a difference in the letter grade from medium to hot temperature could be an indicator of fade. The letters can be in any order. Therefore FE pads fade when hot, and EF pads would not grab when cold.. Also, you should know that Steel on Steel has a C.F. of 0.25!! So EE pads have only marginally more torque than no pads at all! Therefore FF pads are usually considered the minimum for a high-performance pad.

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Better SHO Brakes Through Science
Expected Rotor Temperatures
Capabilities of Various Brake Pads
Pad Part Numbers
DOT Pad Codes
Brake Survey Results
Upgrade Decisions - Rotors vs Pads
On Rotor Warping
Other Brake Maintenance & Modification Tips
Links

 

 

http://ducatigarage.netfirms.com/brakepads.html

 

 

The Chase Test

If you've barely stayed awake reading the previous paragraphs, then grab a cup of java and read on because here's where the good stuff is!

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.

 

Construction

Your brake pads started life in the hands of a friction material formulator, most likely a chemist by degree. Chemists select the composition of a brake pad by choosing from a fixed list of compounds that fall into 4 categories.

Fibers, such as fiberglass, kevlar, arimid, stainless steel, and aluminum maintain the heat stability of the pad. These fibers have various binding strengths and can be organic or metallic. Friction Modifiers such as graphite adjust the friction level and fine tune the performance characteristics of the pad at specific cold and hot temperatures. Fillers take up dead space in the pad. These are generally organic materials with some low frictional effect such as sawdust. Finally, Resins are used to hold the elements of the pad together so they don't crumble apart.