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Wheel Weight Measurement Reference

Chord Length Distance Calculation

Use this reference when the bolt-circle diameter is known and you need to calculate the center-to-center chord length between wheel-weight mounting holes.

What to Measure

Most tractor wheel weights use a 3-hole or 4-hole mounting pattern. Some wheels have 6 or 8 equally spaced mounting holes. In many of those cases, the wheel weight uses every other mounting hole: three locations on a 6-hole wheel, or four locations on an 8-hole wheel.

Count only the holes used to mount the wheel weight. Do not use the holes that mount the wheel to the tractor. For a 6-hole or 8-hole wheel where the weight uses alternating holes, skip one hole as you move to the next mounting location.

For actual wheel-weight fitment, use the direct center-to-center chord-length measurement whenever you can. This calculation is useful when the bolt-circle diameter (BCD/PCD) is known and you need a field-checkable chord length.

Formula & Constants

T = D x C Chord length = bolt-circle diameter x pattern constant
T
The chord length: the straight-line center-to-center distance between two adjacent wheel-weight mounting holes.
D
The diameter of the bolt circle or pitch circle. It is not the overall diameter of the wheel.
C
The constant for the effective mounting pattern shown below.
Effective mounting patternConstant (C)
3 holes0.86603
4 holes0.70711

Use the 3-hole constant when the wheel weight uses three equally spaced locations. Use the 4-hole constant when it uses four equally spaced locations. On a 6-hole or 8-hole wheel, this commonly means using alternating holes.

Center-to-center chord length and bolt-circle diameter diagram A six-hole circular wheel-weight pattern. Chord length T runs from the center of hole 1 to the center of hole 2, skipping one hole. Diameter D runs across the full bolt circle through its center. Chord Length is Simply the Measurement Between Two Points on a Curve. As most wheels and wheel weights are designed using millimeters rather than inches, the calculations can be off very slightly when calculated in inches. This result will still be valid in almost all cases. Diameter used here is the diameter of the bolt circle or pitch circle. It is NOT the overall diameter of the wheel. D T 2. 1. 3.
Chord length is the straight-line measurement between the centers of adjacent mounting holes. Bolt-circle diameter describes the imaginary circle through the hole centers; it is not the overall wheel diameter.

Important: The chord-length measurement shown here is a center-to-center measurement between the mounting holes used by the wheel weight. Do not measure from hole edge to hole edge.

Prefer a printable version? Download the PDF to print or take into the field.

Need Help Identifying Your Wheel-Weight Pattern?

This detailed guide explains how to identify the correct mounting holes, measure chord length accurately, understand 3-hole and 4-hole patterns, and check other fitment details before ordering.

Read the Complete Wheel Weight Mounting Patterns Guide →

Calculation Steps

  1. Identify the wheel-weight mounting holes. Count the mounting locations actually used by the weight. Do not count the wheel-to-tractor lug holes.
  2. Determine the effective pattern. Use 3 holes for a three-location pattern, or 4 holes for a four-location pattern. When a 6-hole or 8-hole wheel uses alternating holes, use the corresponding 3-hole or 4-hole constant.
  3. Obtain the bolt-circle diameter (D). This is the diameter of the circle passing through the centers of the mounting holes - not the outside diameter of the wheel.
  4. Multiply D by the correct constant (C). The result is T, the calculated center-to-center chord length between adjacent mounting locations.
  5. Cross-check the wheel before ordering. Confirm the directly measured chord length, hole diameter, mounting face, and available clearance for the product you are considering.

Worked Example

Known 3-hole bolt circle: 16 7/8 in. (16.887 in.)

This example uses a 3-hole wheel-weight pattern, so the constant is 0.86603.

16.887 x 0.86603 = 14.6246 in.

The calculated chord length is approximately 14 5/8 in. A compatible wheel-weight mounting pattern could be described as 3 @ 14 5/8, subject to confirmation of hole diameter, mounting face, and product-specific fitment.