Brake Pad Friction Codes Explained: EE, FF, GG, and HH

You may see FF, GG, or HH stamped on a brake pad, printed on its box, or listed in an online specification. The letters are useful, but they are often misunderstood.

They are not a material label, a quality score, or proof that one pad will stop your vehicle in a shorter distance. Under SAE J866, the two letters classify two laboratory friction-coefficient averages obtained from testing conducted under SAE J661. They help you decode a marking and compare one piece of published data. Vehicle approval still requires the correct application and product documentation.

Quick answer: Use the friction code to understand two reported friction bands. Choose the pad by exact vehicle and axle fitment, brake hardware, intended use, operating temperature, and the manufacturer's application data.

Illustrative marking anatomy. Actual order and placement vary by manufacturer. Always verify the complete physical marking and part number.

What Do EE, FF, GG, and HH Mean?

The first letter is the normal friction coefficient classification. The second is the hot friction coefficient classification. A matching pair means both calculated averages fall within the same band.

For example, FF represents a band rather than an exact coefficient of friction of 0.40. Both classified averages fall inside F. An FF pad near the lower end of that band can therefore differ meaningfully from another FF pad near the upper end.

Source: SAE J866_201903, Friction Coefficient Identification and Environmental Marking System for Brake Linings.

The normal coefficient is calculated from measurements at 200, 250, 300, and 400 degrees F (93, 121, 149, and 204 degrees C). The hot coefficient uses specified elevated-temperature and recovery readings in the SAE J661 procedure. These are prescribed laboratory conditions, not a direct translation of "the first stop out of the driveway" versus "track temperature."

The current procedure is SAE J661_202604. SAE lists the 2021 revision as historical.

SAE J661 and J866 Do Different Jobs

SAE J661 establishes a laboratory procedure for obtaining and reporting brake-lining friction and wear data. SAE J866 provides the identification and marking framework that converts relevant results into letter classifications.

That distinction matters because a J866 code is a summary, not a complete performance test. SAE states that J866 does not establish brake-lining friction requirements, does not identify every characteristic needed for overall brake performance, and cannot reliably predict complete brake-system performance by itself.

In other words, J661 produces defined test data; J866 gives part of that data a common identification language.

How to Read FF, FG, GF, GG, GH, and HH

Mixed codes are read in the same order: normal classification first, hot classification second.

A mixed code is easy to overread. FG merely places the hot average one band above the normal average; it cannot prove weak cold bite or a warm-up requirement. GF places the hot average one band lower, without proving unacceptable fade. Those judgments require the product's full friction-versus-temperature behavior, pressure sensitivity, fade and recovery data, and intended application.

What the Friction Code Can and Cannot Tell You

This is the most important buying boundary in the article: a friction code is useful evidence, but it is not a fitment or performance approval.

Is GG Better Than FF? Does HH Stop Faster?

A higher letter represents a higher classified friction band. If brake hardware, clamp force, rotor radius, temperature, and every other relevant condition were unchanged, a genuinely higher working coefficient of friction could produce more brake torque or require less pedal input for similar torque.

Only product-level test data can show the working coefficient at a specific temperature and pressure. The two letters omit the complete friction curve between test points.

Two hypothetical FF pads show why:

• Pad A has normal and hot averages of 0.36.
• Pad B has normal and hot averages of 0.44.

Both are FF, but their averages sit near opposite ends of the F band. They may also differ in compressibility, modulation, noise, wear, rotor interaction, and behavior between the reported test points.

Stopping distance introduces additional limits. The tire-road interface determines how much force the vehicle can transmit before the tire slides. ABS manages brake pressure as a wheel approaches lockup; it does not create tire grip. Vehicle load, road surface, brake balance, pad and rotor temperature, hardware condition, and driver input also affect the result. See Bosch's explanation of antilock braking systems.

For a daily-driven car with factory calipers, OE-size rotors, street tires, and a low-noise requirement, a properly documented FF replacement may be a better decision than an unknown GG or HH pad with unclear fitment and operating behavior.

Can You Replace FF Pads With GG or HH?

The two-letter code is insufficient to approve the replacement. Start with the brake application, then use the code as one comparison point.

Changing only one axle also requires care. A compound that changes working friction can alter the mechanical front-to-rear torque relationship under the same operating conditions. ABS, electronic brake-force distribution, and stability control can manage pressure when slip develops, but they do not make every arbitrary front/rear compound pairing equivalent to the vehicle's intended balance.

Use exact manufacturer or vehicle application guidance before mixing compounds. If that guidance is unavailable, consult a brake specialist who can evaluate the entire configuration.

How to Verify a Brake Pad Code Before Buying Online

Online product titles are often reused across broad vehicle groups. A seller may also copy an old specification while the manufacturer has revised a formulation or part number. Use this sequence:

1. Confirm the exact manufacturer part number.
2. Match the vehicle, trim, brake package, and front or rear axle.
3. Request a current photo showing the product and its complete marking.
4. Compare the marking with the manufacturer's current technical page or data sheet.
5. Use AMECA's Public Materials Listing as a supporting check where applicable.
6. If the listing, part number, marking, and manufacturer data conflict, pause the purchase and ask for written clarification.

AMECA's public guidance states that its portal can be searched by manufacturer or edge code. Treat that as supporting evidence, not as a stand-alone counterfeit test or vehicle-fitment database.

The full marking may include manufacturer, formulation, friction, environmental, and date-related information. The final two visible characters are therefore not automatically the friction code. Read the complete string and verify its format instead of guessing from a cropped marketplace photo.

Friction Code Is Not Brake Pad Material

Ceramic, semi-metallic, low-metallic, and organic describe formulation families. EE, FF, GG, and HH describe classified friction bands. There is no reliable one-to-one mapping between them.

Material labels help narrow the options, but they do not complete the selection. For a formulation-focused comparison, use a dedicated ceramic-versus-semi-metallic guide and then verify the exact product data.

Choose by Driving Duty, Then Check the Code

The duty determines which product data you need. The code contributes one data point; track and towing suitability must come from the complete application and operating data.

Installation and Bedding Still Matter

Follow the bedding procedure supplied for the exact pad and rotor combination. Many compounds depend partly on forming a controlled, even transfer layer on the rotor; the balance between adherent and abrasive friction varies by formulation. A universal speed, stop count, or mileage is therefore inappropriate.

If braking feel, noise, or vibration changes after a pad swap, inspect rotor condition, hardware, caliper operation, pad fit, and bedding before blaming the friction code. Ferodo's brake-judder technical guidance explains how disc-thickness variation and uneven deposits can contribute to judder.

Frequently Asked Questions

Is FF a good brake pad rating?

FF means the normal and hot calculated averages both fall within the F band. Whether it is a good choice depends on the exact product, vehicle application, axle, rotor, duty, and required trade-offs.

Is GG better than FF for street driving?

Not automatically. GG represents higher classified averages, but a correctly matched FF pad can be the better street product when it provides the required fitment, control, comfort, and documented operating behavior.

What does HH mean on brake pads?

HH means both classified averages are above 0.55. Material, track suitability, and the complete friction curve remain unknown.

Can front and rear pads use different friction codes?

Some vehicle designs do use different front and rear formulations, but owners should not create a pairing from the letters alone. Follow exact vehicle and axle application guidance.

Use the Code as One Buying Check

EE, FF, GG, and HH are valuable because they turn two laboratory friction averages into a common identification system. Their value ends where vehicle-specific judgment begins.

Confirm the vehicle, brake package, axle, part number, rotor, and intended duty first. Then compare the friction code with the manufacturer's operating data, wear and NVH information, bedding procedure, and application guidance. That sequence protects you from the two most common mistakes: buying a pad because its letters look more impressive, or trusting an online listing that conflicts with the physical product.

Need a friction-code and fitment check? Send the year, make, model, trim, front or rear axle, current pad part number or complete marking, brake modifications, and intended use. ICOOH can use that information to identify compatible braking options; the final installation decision should follow the exact product and vehicle documentation.

Sources

1. SAE International. SAE J866_201903: Friction Coefficient Identification and Environmental Marking System for Brake Linings.
2. SAE International. SAE J661_202604: Brake Lining Quality Test Procedure.
3. Automotive Manufacturers Equipment Compliance Agency. Brake Environmental Certification: General Public.
4. Bosch Mobility. Antilock Braking System.
5. Ferodo. Brake Judder Technical Tip.