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SAE J1255 Specification Definitions for Feller Bunchers: A Comprehensive Guide
SAE J1255, developed by the SAE Machine Technical Committee—Forestry and Logging, established a uniform method for defining specification terms for feller bunchers. Although superseded by J/ISO 13862, this standard remains a foundational reference for understanding the dimensional, mass, and performance characteristics of both wheeled and track-type feller bunchers. All measurements are to be taken on a level surface, and conditions such as track shoe type, tire size and inflation pressure, ballast, and articulation state must be reported to ensure repeatability.
Key Specification Definitions
The following table summarizes the key dimensional and performance parameters defined in SAE J1255. Each parameter has a designated letter used in the standard’s figures.
| Parameter | Description |
|---|---|
| Operating Mass | As defined in SAE J1234; includes machine with all standard equipment, full fuel, and specified ballast. |
| A – Overall Length | Horizontal distance from rearmost point to forwardmost point of felling head at maximum reach on level ground. |
| B – Overall Height | Vertical distance from ground to highest point of machine under the same conditions as A. |
| C – Overall Width | Transverse distance between extreme side points with felling head positioned as in A. |
| D – Wheelbase / Track on Ground | Per SAE J1234; distance between front and rear axle centers or track contact length. |
| E – Track Gauge or Thread | Transverse distance between track centerlines or wheel centers at ground level (front and rear if different). |
| F – Ground Clearance | Minimum clearance under the machine as defined in SAE J1234. |
| GF, GR – Upperstructure Longitudinal Tilt | Maximum angle the levelling mechanism can tilt the upperstructure forward or rearward. |
| HR, HL – Upperstructure Side Tilt | Maximum tilt angle to right or left in a plane perpendicular to the machine’s longitudinal centerline. |
| I1, I2 – Felling Head Longitudinal Tilt | Maximum tilt of felling head vertical centerline forward or rearward about its pivot (with head positioned as in A). |
| JR, JL – Felling Head Side Tilt | Maximum rotation of felling head to right or left perpendicular to longitudinal centerline. |
| K – Cutting Distance (Min) | Horizontal distance from boom mast/turntable axis/front axle to felling head tree centerline at ground level, minimum reach. |
| L – Cutting Distance (Max) | Same as K but at maximum reach at ground level. |
| M – Cutting Distance (Above Ground) | Horizontal distance when felling head is at its maximum height above ground. |
| N – Cutting Distance (Below Ground) | Horizontal distance when felling head is at its maximum depth below ground. |
| O – Machine Cutting Depth | Maximum vertical distance from ground level to bottom of cutting edge when tree centerline is vertical. |
| P – Maximum Cutting Height | Maximum vertical distance from ground level to bottom of cutting edge when tree centerline is vertical. |
| QR, QL – Boom Swing | Angle from machine longitudinal axis to boom longitudinal center at maximum right/left swing. |
| R – Machine Clearance Circle | Smallest diameter circle enclosing machine with no brakes, felling head at ground, and full articulation (if applicable) per SAE J1234. |
| S – Minimum Swing Circle | Smallest diameter described by outermost point of machine or felling head during full turntable/boom swing with head close to machine. |
| T – Tail Swing Radius | Maximum radius from rotation centerline to outermost upperstructure point with levelling table parallel to ground. |
| U – Loaded Tire Radius | Vertical distance from wheel center to ground. |
| V – Minimum Stump Height | Vertical distance from bottom of felling head to bottom of tree cutting edge. |
🛠️ Design Insight: By mandating consistent conditions, the standard enables engineers and buyers to compare different feller buncher models objectively. For example, specifying that dimensions are taken with the levelling mechanism parallel to the ground and the felling head at maximum reach ensures that all measurements are reproducible.
Engineering Insights, Common Mistakes, and FAQs
⚠️ Common Mistake: Confusing overall height (B) with maximum cutting height (P). Overall height is a transport/storage dimension, while cutting height describes the machine’s working envelope. Always verify which parameter is being reported.
Other frequent errors include failing to specify track shoe or tire details when stating operating mass, not declaring the articulation angle for articulated machines, and assuming all dimensions are taken with the felling head in the same position. Remember that overall length (A) uses the felling head at maximum reach, while cutting distances (K through N) require the tree centerline to be perpendicular to the ground.
How is overall length (A) measured per SAE J1255?
Overall length is the horizontal distance from the rearmost point of the machine to the forwardmost point of the felling head. The measurement is taken on a level surface with the levelling mechanism parallel to the ground and the felling head positioned on the ground at maximum reach. Track shoe type, tire size and pressure, ballast, and articulation state (if applicable) must be stated.
What is the difference between felling head longitudinal tilt and upperstructure tilt?
Felling head longitudinal tilt (I1 and I2) is the angle the felling head rotates forward or rearward about its own pivot, independent of the chassis. Upperstructure longitudinal tilt (GF and GR) is the angle provided by the levelling mechanism to tilt the entire upperstructure relative to the undercarriage. Both are measured in degrees but describe movement of different parts of the machine.
How is average ground pressure calculated according to this standard?
Average ground pressure is obtained by dividing the operating mass (as defined in SAE J1234) by the ground contact area (also per SAE J1234). The result is expressed in kilopascals. It is critical to include the correct contact area based on track dimensions or tire footprint and to state the ballast and inflation pressure used.
Why must the articulation angle be specified for measurements on articulated machines?
For articulated machines, dimensions such as overall width and clearance circle change with the articulation angle. SAE J1255 requires that all specifications be given with the axles parallel unless otherwise noted. For clearance circle (R), the machine must be fully articulated. Not stating the articulation condition can lead to non‑repeatable measurements.
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