Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
SAE J2707:2021 Wear Test Procedure for Brake Friction Materials – A Comprehensive Overview
Brake friction material wear is a critical factor in vehicle safety and performance. To standardize how manufacturers evaluate wear characteristics, SAE International published the J2707 Recommended Practice, which provides a rigorous inertia dynamometer test procedure. The 2021 revision harmonizes with other standards, expands test ranges, and introduces a common burnish schedule to improve repeatability and realism. This article explores the structure, methods, and best practices of SAE J2707:2021 for engineers and test professionals.
Understanding the Scope and Key Updates
SAE J2707:2021 specifies dynamometer test procedures for assessing wear rates of automotive service brake linings (brake shoes) and disc brake pads. The standard aims to replicate actual driving conditions through controlled speed, temperature, and deceleration profiles. Major updates in the 2021 revision include:
- Harmonization with SAE J2789 for inertia calculation and SAE J2986 for wear measurements.
- Extension of Method A to include low deceleration (below 0.3 g) and low temperature (below 100°C) tests, reflecting modern driving patterns such as WLTP.
- Expansion of Method B (block wear) with separate temperature conditions for front and rear brakes and lower energy levels.
- Adoption of a common burnish schedule consistent with FMVSS 135 to ensure consistent pre-test conditioning.
Engineering Design Insight 🛠️ Wear behavior is strongly influenced by temperature, speed, and deceleration. The standard emphasizes testing across a realistic range of these parameters, enabling engineers to evaluate transfer layer phenomena and material compatibility under varied operating conditions. This approach helps in selecting friction materials that maintain performance and longevity in actual vehicles.
In-Depth Look at Method A and Method B
The standard defines two primary test methods, each addressing different wear characterization needs.
| Method | Objective | Key Test Parameters |
|---|---|---|
| Method A – Wear vs. Temperature | Quantify wear sensitivity to lining/rotor temperature | Multiple temperature setpoints, deceleration levels (including low deceleration), high-speed snubs |
| Method B – Block Wear | Evaluate wear under variable speed, deceleration, and temperature profiles mimicking real-world driving | High energy block test (B1) and moderate energy block test (B2) with separate front/rear conditions |
Method A includes three sub-procedures: general wear test (A1), low deceleration wear test (A2), and high speed wear test (A3). The low deceleration test is new in the 2021 revision and addresses friction materials containing ferrous metals that exhibit different wear mechanisms at low loads. Method B consists of two block wear sequences—high energy (B1) and moderate energy (B2)—that simulate aggressive and normal driving patterns. Both methods require a standardized burnish to condition the friction pair before measurements.
Critical Considerations for Accurate Results
To achieve reliable wear measurements, engineers must pay careful attention to several test conditions. The inertia calculation must follow SAE J2789 exactly, and wear measurements need compliance with SAE J2986. Temperature measurement is specified for the disc/drum and optionally for pads/shoes. Cooling air velocity and direction must be controlled and measured. Sampling rate and pressure ramp rate also affect data quality.
Common Mistakes ⚠️ Incorrect inertia calculation, inaccurate wear measurement not aligned with SAE J2986, and inadequate burnish conditioning are frequent pitfalls. Additionally, neglecting to adjust test parameters for low deceleration or low temperature conditions in Method A can lead to unrepresentative wear rates.
Frequently Asked Questions
What is the purpose of the burnish schedule in SAE J2707?
The burnish schedule conditions the friction pair before the actual wear test, ensuring a consistent transfer layer and initial wear interface. The 2021 revision adopts a common burnish schedule harmonized with FMVSS 135, reducing variability across different test labs and improving repeatability.
How does Method A differ from Method B?
Method A focuses on wear sensitivity to temperature and includes specific temperature setpoints and deceleration tests (including low deceleration). Method B, the block wear test, uses variable speed, deceleration, and temperature sequences over many snubs to simulate real-world driving patterns like WLTP. Engineers choose based on the application—Method A for material temperature sensitivity, Method B for overall wear life prediction.
What are the key changes in the 2021 revision?
The revision harmonizes with SAE J2789 and J2986, expands the temperature and deceleration ranges for Method A, adds separate temperature conditions for front/rear brakes in Method B, reduces energy levels for moderate block test, and implements a common burnish schedule consistent with FMVSS 135. Typographical errors from previous versions were also corrected.
Why is wear measurement per SAE J2986 important?
SAE J2986 provides a standardized method for measuring friction material wear, ensuring consistency across laboratories. Following this standard is essential for comparing wear results from different tests and for validating material performance against engineering specifications.
SAE J2707:2021 is a vital tool for brake engineers seeking to evaluate wear performance under controlled, realistic conditions. By adhering to the recommended practices and avoiding common pitfalls, testing teams can generate reliable wear data that drives better brake material development and qualification.
