Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
SAE J1517-2024: Driver Selected Seat Position for Class B Vehicles – Seat Track Length and SgRP
Overview of SAE J1517-2024
SAE J1517-2024 is a recommended practice that provides standardized procedures for determining driver seat track location, seat track length, and the Seating Reference Point (SgRP) in Class B vehicles—namely heavy trucks and buses. This revision applies exclusively to Class B vehicles (previously included Class A), aligning with SAE J4004 for passenger cars and light trucks. The standard defines three sets of linear equations for driver selected seat position lines, based on male-to-female driver population ratios: 50:50, 75:25, and 90:10 to 95:5. These equations allow engineers to calculate the horizontal H-point location (relative to the accelerator heel point, AHP) as a function of seat H-point height (H30). The SgRP is consistently defined as the 95th percentile seat position line for a 50/50 driver population, enabling uniform application across manufacturers.
🔍 Key Insight: Class B vehicles typically feature flat treadle accelerator pedals and horizontal fore/aft seat travel paths. The procedures in J1517 are calibrated specifically for this configuration—do not use Class A equations from SAE J4004 for heavy truck designs.
Driver Selected Seat Position Accommodation Lines
Equations are provided for seven percentile levels (2.5, 5, 10, 50, 90, 95, 97.5) for each of the three driver population mixes. The general form is: X_i = a – b × z, where X_i is the horizontal seat position (mm aft of AHP) for the i-th percentile, and z is the vertical H-point height above AHP (mm). The table below lists the equations for the 50:50 male-to-female population, as an example.
| Percentile | Equation (X_i in mm) |
|---|---|
| 97.5 | X = 916.50 – 0.471z |
| 95 | X = 900.23 – 0.471z (SgRP line) |
| 90 | X = 888.44 – 0.487z |
| 50 | X = 798.74 – 0.446z |
| 10 | X = 668.97 – 0.340z |
| 5 | X = 637.76 – 0.317z |
| 2.5 | X = 625.21 – 0.327z |
Equivalent sets exist for the 75:25 and 90:10–95:5 mixes. Derivation is based on anthropometric data from heavy truck driver studies (Sanders, 1983; Shaw and Sanders, 1984). The SgRP line—the 95th percentile for a 50/50 population—is the recommended reference for defining the Seating Reference Point across all vehicles.
Procedure for Seat Track Length and SgRP Determination
The standard outlines a step-by-step method for locating the seat track and calculating required travel length to accommodate a desired percentage of the target driver population.
- Determine the Accelerator Heel Point (AHP) per SAE J1516.
- Establish H30: For a horizontal design H-point travel path, H30 is simply the height of that path above AHP. For an inclined path, first locate the SgRP (intersection of design H-point travel path with the SgRP line) and take the vertical distance from AHP to SgRP.
- Select the appropriate accommodation line set based on the expected male-to-female driver population ratio (50:50, 75:25, or 90:10–95:5). The 50th percentile line should align with the Accommodation Tool Reference Point from SAE J1516.
- Determine the design H-point travel path (typically horizontal for most heavy trucks).
- Find the intersection points of that travel path with the 2.5 and 97.5 percentile accommodation lines. The distance between these two intersections defines the required seat track length to accommodate 95% of the targeted population. The mid-point of that interval can be used to position the track.
⚠️ Common Pitfall: Misinterpreting the SgRP as the rearmost track position. The SgRP is a design reference point, not necessarily the full-rear seat stop. Also, ensure AHP location is consistent with SAE J1516—an incorrect AHP shifts all accommodation lines.
🛠️ Engineering Design Insight: The linear equations simplify the design of seat track systems, allowing rapid calculation of minimum travel to meet accommodation targets. Using the SgRP as a common reference across vehicles enables consistent reporting of key interior dimensions (e.g., SAE J1100) and facilitates benchmarking between models.
Frequently Asked Questions
What male-to-female driver ratio should I assume for my heavy truck design?
The choice depends on the expected driver demographics. The standard offers three mixes: 50:50 (balanced), 75:25 (male majority), and 90:10–95:5 (high male proportion). If no specific data is available, using the 50:50 mix with the SgRP line for reference is a common starting point. However, fleet operators may specify a different mix.
How is the SgRP determined from the equations?
The SgRP is defined by the 95th percentile equation for the 50:50 male-to-female population. Locate the design H-point travel path, then find the intersection with that line (X = 900.23 – 0.471z). This point is the Seating Reference Point, used as the datum for several SAE J1100 dimensions.
Can the same equations be used for seats with vertical adjustment?
Yes, the procedure works with vertically adjustable seats as long as the design H-point travel path (mid-height of vertical adjustment) is used for calculations. The equations accept any H-point height z (H30). Ensure the seat is loaded with an SAE H-point machine when measuring.
How do I validate that the seat track accommodates the target population?
After positioning the track, check that the H-point travel path intersects the 2.5 and 97.5 percentile lines for the chosen mix. The track length must be at least the horizontal distance between these intersection points. A longer track may be needed if vertical adjustment or other design constraints impose offsets.
