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SAE J2717-2018: Standardized Tests for Tire Geometry, Mass, and Inertias đ ī¸
SAE J2717-2018 is a recommended practice that defines three test methods to determine basic tire geometry, mass, and moments of inertia. These measurements are essential for building accurate road load models and for comparative evaluations in tire research and development. The standard applies to any tire size provided the equipment is properly scaled, and it emphasizes that no specialized machines are required—simple jigs and tools can be used effectively. This article outlines the three procedures, key equipment, engineering insights, and common pitfalls to ensure accurate and repeatable results.
The Three Measurement Procedures
SAE J2717 specifies three distinct procedures, each focused on a different set of properties. The first procedure measures the tire’s undeflected radius, section width, and section height. The second determines the mass of the tire and wheel separately. The third procedure uses a torsional pendulum to measure moments of inertia about the X”, Y”, and Z” axes as defined in SAE J2710. Together, these data enable accurate force predictions in road load models and support comparative studies of tire characteristics.
| Procedure | Measurement | Equipment / Tools |
|---|---|---|
| Geometry | Undeflected radius, section width, section height | Measuring tape, calipers, ruler |
| Mass | Tire mass, wheel mass | Scale or balance |
| Inertias | Moments of inertia about X”, Y”, and Z” axes | Torsional pendulum, timing device, calibration inertia |
The axis system for inertia measurements is based on SAE J2710, with the origin at the intersection of the spin axis and the wheel plane. Due to possible offset of the center of gravity along the Y” axis from an offset wheel disc or tire asymmetries, the parallel-axis theorem must be applied if needed. The standard also references calibration requirements per ISO/IEC 17025 and safety guidelines from OSHA Standard 1910.177 for servicing multi-piece rims.
Engineering Insights and Best Practices
The design of SAE J2717 deliberately avoids reliance on purpose-built machinery, allowing labs to use common measurement tools and a torsional pendulum for inertia testing. This approach reduces cost and complexity, making the standard accessible for a wide range of testing environments. Key engineering insights include:
- The torsional pendulum method requires careful calibration and timing to achieve repeatable results.
- The parallel-axis theorem correction is critical when the center of gravity does not align with the axis system origin.
- All measuring tools must be calibrated annually with traceability to national standards.
Design Insight: The standard’s emphasis on using jigs and readily available tools means that engineers can implement these tests without investing in expensive, dedicated equipment. This lowers the barrier to obtaining high-quality tire data for modeling and development.
Common Mistake: Forgetting to account for the Y” axis center-of-gravity offset when calculating moments of inertia. Always verify the c.g. location and apply the parallel-axis theorem if necessary to avoid errors in your road load model parameters.
Frequently Asked Questions
Q1: What is the purpose of SAE J2717?
A1: It provides standardized, repeatable procedures for measuring tire geometry, mass, and inertias for use in road load models and comparative testing during research and development.
Q2: What equipment do I need for inertia measurements?
A2: A torsional pendulum, a precision timing device, and a calibration inertia. No special-purpose machine is required; many labs can construct suitable pendulum setups.
Q3: How is the tire undeflected radius defined?
A3: It is defined as half the tire overall diameter, consistent with SAE J2047.
Q4: Do I need to consider offset of the center of gravity?
A4: Yes. If there is an offset along the Y” axis (common with offset wheel discs or tire asymmetries), you must apply the parallel-axis theorem to correct the inertia values to the axis system origin.
For complete details, refer to the full SAE J2717-2018 document. Ensure your laboratory quality system conforms to ISO/IEC 17025 for proper documentation and calibration.
