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Low Speed Enveloping Test with Perpendicular and Inclined Cleats (SAE J2731)
This SAE Recommended Practice, J2731, defines a standardized method for measuring spindle forces and moments as a tire rolls over a rectangular cleat at very low speed. The test is critical for developing road load models and evaluating tire performance. 🔍 The method yields force and moment histories that are essentially free from tire non-uniformity effects, making it ideal for comparative studies.
Purpose and Application
The test method applies to any tire size when equipment is properly scaled. It supports research and development, parameter determination for road load models, and comparative property evaluations. The cleat can be oriented perpendicular (90°) to the tire path or optionally at an inclined angle, allowing evaluation of different obstacle geometries. Data from the test help engineers refine vehicle dynamics simulations and optimize tire design.
Test Apparatus and Configuration
The test machine (drum or flatbed) must allow at least a quarter revolution before the cleat is encountered, and preferably a full revolution to allow relaxation phenomena to complete. The instrumented spindle measures three forces (FX”, FY”, FZ”) and two moments (MX”, MZ”) as the tire rolls over the cleat. The loading system maintains a slip angle within ±0.05° and an inclination angle within ±0.05°, with normal force accuracy of ±1.0% of full scale. The cleat is mounted on the test surface and can be positioned perpendicular to the path or at a desired angle. 🛠️ Table 1 summarizes the measured channels and their symbols.
| Symbol | Defined Term |
|---|---|
| FX” | Longitudinal Force |
| FY” | Lateral Force |
| FZ” | Normal Force |
| MX” | Overturning Moment |
| MZ” | Aligning Moment |
Distance traveled (D) and tire angular displacement (Φ) are recorded using absolute encoders. The speed of travel does not need to be constant because angular displacement is directly measured.
⚠️ Common Mistake: Failing to allow sufficient tire revolution before cleat engagement can introduce relaxation transients. A full revolution is preferred to ensure repeatable results.
Data Acquisition and Quality Considerations
The laboratory performing the test must have a quality system conforming to ISO 17025 or equivalent. Environmental vibration isolation is essential to avoid contaminating force and moment signals. Prior to installation, the machine’s environment should be tested for structure-borne vibrations; if significant, mitigation practices from SAE J2730 or suitable data filtering must be applied. 📐 Engineering Insight: The rigid spindle constraint approximates fixed loaded radius, simplifying interpretation of force and moment data for model calibration. The data are suitable for determining parameters for road load models, predicting spindle forces from irregular surfaces.
🔍 Note: The standard explicitly states that speed does not need to be constant because angular displacement is directly measured, providing flexibility in test execution.
Frequently Asked Questions
1. What is the difference between the perpendicular and inclined cleat orientations?
The perpendicular cleat (90°) is the standard configuration. The inclined option allows engineers to study oblique impacts, providing more comprehensive data for road load model development.
2. What forces and moments are measured during the test?
The instrumented spindle measures three forces: longitudinal (FX”), lateral (FY”), and normal (FZ”), and two moments: overturning (MX”) and aligning (MZ”).
3. Can the test be performed on any tire size?
Yes, the method applies to any size tire so long as the equipment is properly scaled to accommodate the intended test tire.
4. How is data synchronized with tire position?
Absolute encoders measure the distance traveled (D) and tire angular displacement (Φ), ensuring accurate phase alignment even if speed varies during the test.
