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 Although superseded by J/ISO 13862, this standard remains a foundational reference for understanding the dimensional, mass, and performance characteristics of both wheeled and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.

Engineering Insights, Common Mistakes, and FAQs

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.