Overall Distance

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R&A Rules Limited
and
United States Golf Association

ACTUAL LAUNCH CONDITIONS
OVERALL DISTANCE AND SYMMETRY
TEST PROCEDURE
(PHASE II)

Revision 1

June 1, 2004

1. Scope

1.1 This method covers the procedure for performing the overall distance and symmetry conformance tests for golf balls as administered by the United States Golf Association (USGA).

1.2 The results of the conformance tests are used by R&A Rules Limited (R&A) and the USGA in determining conformity of the golf balls to the Rules of Golf.

1.3 The values stated in imperial units are to be regarded as standard. The values stated in SI units are for information only.

2. Applicable Documents

2.1 R&A and USGA documents:

  • Rules of Golf
  • Conforming Ball List
  • The Indoor Test Range (ITR) Technical Description and Operation Manual, Version 2

USGA Indoor Test Range (ITR) DataAnalysis Software, Version 2.0.0

3. Summary of Method

3.1 Using equipment at the USGA Research and Test Center, currently referred to as the Indoor Test Range (ITR), the golf balls are completely characterised by the coefficient of lift (CL), and coefficient of drag (CD).

3.2 Using the aerodynamic coefficients, the overall distance (carry plus roll) of a sample lot, as well as its spherical symmetry, is determined for a specific combination of launch conditions (ball speed, spin rate and launch angle) as determined by a mechanical golfer.

4. Significance

4.1 This method is used to determine the overall distance and symmetry of golf balls for a given set of launch conditions. The data obtained from this method is used to ascertain the conformance of the golf balls to the Overall Distance and Symmetry Standards as stated in the Rules of Golf (Appendix III).

The overall distance of the ball shall not be greater than 317.0 yards. A maximum test tolerance of 3.0 yards is associated with this test.

In addition, the ball must not be designed, manufactured or intentionally modified to have properties that differ from those of a spherically symmetric ball. A spherically symmetric ball shall not exhibit statistically significant differences in carry distance greater than 4.0 yards or in flight time of more than 0.40 seconds regardless of which axis the ball is spinning about when launched.

4.2 Letters are sent to the golf ball manufacturers advising of those brands of golf balls that do not conform to the Overall Distance or Symmetry Standards or which fall within the test tolerances.

4.3 Only those balls that have already passed the conformance tests for Weight, Size, and Initial Velocity will be tested for conformance to the Overall Distance and Symmetry Standards.

4.4 Golf balls that conform to the Weight, Size, Initial Velocity, Symmetry, and Overall Distance Standards are included inthe Conforming Ball List, published monthly by the R&A and USGA.

4.5 Intermediate screening procedures may be used to determine ball conformance and increase testing efficiency. However, no ball will be ruled non-conforming unless it has been tested according to this protocol.

5. Determination of Launch Conditions

5.1 At this point in the conformance testing process the balls should be separated into two individual boxes labeled Dozen 1 and Dozen 2. Each ball should have a USGA Lot number as well as an individual ball number. Verify that the markings and the USGA Lot number on the balls match those on the boxes and that balls numbered 1 through 12 are contained in Dozen 1 and that balls numbered 13 through 24 are contained in Dozen 2.

5.2 Identify and mark the seam and pole locations on balls numbered 13 through 24. (Figure 5.2)

5.3 Once the balls are properly marked, they should be stored in the incubator at a temperature of 75.0±1.0°F (23.9°C) for at least 3 hours.

figure 5.2

Figure 5.2 - Ball Pole and Seam Marks

5.4 Ensure good mechanical operation and proper warm-up of the mechanical golfer.

5.5 Verify calibration of the mechanical golfer by hitting 6 "USGA/R&A Calibration" balls and measuring the launch conditions.

5.5.1 If the average value of the launch conditions falls within the ranges specified in Table 5.5 then proceed to step 5.6.

5.5.2 If the average value of any of the launch conditions falls outside of the ranges specified in Table 5.5 then the mechanical golfer setup must be re-calibrated and Section 5 repeated.

Table 5.5 - Mechanical Golfer Calibration Conditions

Launch ConditionMean Acceptable Range
Angle 10° ±0.5°
Spin 42 rps ±2.0 rps
Swing Speed 120 mph ±0.5 mph
Ball Speed 256 fps Reference*
* The reference ball speed of 256 fps represents the speed
after initial aging to a near steady-state condition.

5.6 Place ball 13 of the sample lot on the tee and strike it so that it is launched to produce a back spin about an axis described by a line that would pass through the poles of the ball and that would lie in horizontal plane and be perpendicular to the direction of flight (Figure 5.6.) This orientation is referred to as "poles horizontal" (PH).

5.7 Measure and record the launch angle, spin rate and velocity for the shot.

5.8 Repeat steps 5.6 through 5.7 for balls 14 through 24.

5.9 Calculate the means of the launch angle, back spin and speed values measured in steps 5.7 and 5.8. These are the launch conditions for the sample lot that will be used to determine conformance to the Overall Distance and Symmetry Standards.

(To maximize testing efficiency multiple sample lots may be tested during a single session. When multiple lots are tested, calibration of the mechanical golfer, step 5.5, should also be performed at the conclusion of testing.)

6. Determination of Aerodynamic Properties

6.1 Ensure that the room temperature is kept at 75±3°F (23.9°C).

6.2 Measure the outside diameter of balls numbered 13 through 24 along three axes, one from pole to pole and in two orthogonal directions across the seam (equator), and calculate the average ball diameter.

6.3 Ensure good mechanical operation and proper warm-up of the test equipment.

6.4 Set the launcher wheel speeds to produce the desired ball velocity and spin rate described in the ITR Manual.

6.5 Fire six calibration balls down the range. After each shot verify that data was obtained from each measurement station and that the predicted CL and CD are within the allowable range.

(Note: The allowable range is set at ±5% of the expected nominal value of the CL and CD for the calibration ball. This step is used as a gross indicator of potential ITR problems not as a statistical process control.)

6.6 Repeat 6.5 using balls 13 through 24 of the test lot with the balls launched in the "poles horizontal" (PH) orientation (i.e. such that they spin about an axis described by a line that would pass through the poles of the ball and that would lie in horizontal plane and be perpendicular to the direction of flight, Figure 5.6.)

6.7 Repeat step 6.6 using balls 13 through 24 of the test lot with the balls launched such that they spin about the axis described by a line that would pass through the seam (equator) of the ball and that would lie in horizontal plane and be perpendicular to the direction of flight (Figure 6.7.) This orientation is referred to as "pole-overpole" (PP).

(To maximise testing efficiency multiple sample lots may be tested during a single session.)

6.8 Repeat steps 6.4 through 6.7 until data has been obtained at each of the full set of 15 test settings (i.e. launch velocity and spin rate) described in the ITR Manual.

(Note: The R&A and USGA reserve the right to change the settings at any time to increase the accuracy and/or efficiency of the test.)

6.9 From the data collected in steps 6.5 through 6.8, calculate the coefficients of lift (CL) and drag (CD) for the calibration ball and both orientations of all tested sample lots. (Ref. USGA Indoor Test Range (ITR) Data Analysis Software, Version 2.0 and The ITR Technical Description and Operation Manual, Version 2)

6.10.1 If the calibration ball performance is within acceptable limits then proceed to step 7.

6.10.2 If the calibration ball performance is not within acceptable limits, then the ITR must be re-calibrated and step 6 repeated.

figure 5.6

Figure 5.6 - Poles Horizontal (PH) Ball Orientation

figure 6.7

Figure 6.7 Poles over Pole (PP) Ball Orientation

7. Conformance Determination

7.1 Using the launch conditions calculated in section 5 and the CL and CD calculated in step 6.9, determine the carry distance, overall distance and flight time at standard environmental conditions (75°F, 30.0 in Hg and 50% relative humidity) for the sample lots in both orientations, PP and PH. (Ref. USGA Indoor Test Range (ITR) Data Analysis Software, Version 2.0.0 and The ITR Technical Description and Operation Manual, Version 2)

7.2 Overall Distance Evaluation

7.2.1 From the overall distances calculated in 7.1, select the orientation (PP or PH) that produces the greatest overall distance for the sample lot.

7.2.2 If the overall distance determined in 7.2.1 is less than 317.0 yards then the overall distance evaluation is complete and the sample lot conforms to the Overall Distance Standard of the Rules of Golf.

7.2.3 If the overall distance determined in 7.2.1 is greater than 317.0 yards but less than or equal to 320.0 yards then the overall distance evaluation is complete and the sample lot conforms to the Overall Distance Standard of the Rules of Golf. However, a warning letter should be issued to the manufacturer informing them that the overall distance of the sample lot falls within the test tolerance. Any future tests of balls with identical markings from any source could result in a ruling of non-conformance to the Overall Distance Standard.

7.2.4 If the overall distance determined in 7.2.1 is greater than 320.0 yards the ball does not conform to the Rules of Golf.

7.3 Symmetry Evaluation

7.3.1 Using the launch conditions calculated in Section 5 and the CL and CD calculated in step 6.9, determine the carry distance, and flight time at standard environmental conditions (75°F, 30.0 in Hg and 50% relative humidity) for the sample lots in both orientations, PP and PH. (Ref. USGA Indoor Test Range (ITR) Data Analysis Software, Version 2.0.0 and The ITR Technical Description and Operation Manual, Version 2)

7.3.2 Calculate the differences between the carry distances and times of flight for each ball in the two orientations and compute the mean of these differences

7.3.3 If the mean of the differences in the carry distance calculated in 7.3.2 is greater than 4.0 yards and that value is statistically significant, or if the mean of the differences in the time of flight is more than 0.40 seconds, and that value is statistically significant, then the sample lot does not conform to the Rules of Golf.

7.3.4 The manufacturer shall be notified that the lot has failed the symmetry test and that the lot will be included in the Conforming Ball List on a conditional basis. The manufacturer shall be requested to take corrective action and re-submit the lot within six-months. If no statistically significant changes in performance are made within that period, then the lot will be removed from the next published list.


Appendix A – Test ball and club specifications:

The test head may be purchased directly from the USGA. The calibration ball is available from Bridgestone Sports. The specifications for these are given below.

Test Head Specifications
Construction: Cast 6-4 titanium body, forged SP-700 titanium face
Manufacturer: Fu Sheng Industrial Co., Ltd
Model: TI-360 USGA

ParameterUnitsNominal Value
Face Depth inches (mm) 2.0 (51)
Face Width inches (mm) 3.9 (99)
Mass ounces (grams) 7.0 (198)
Volume cubic inches (cc) 22.0 (360)
Hosel Diameter inches (mm) 0.339 (8.61)
Lie degrees 58
Loft degrees 9
Bulge inches (mm) 12.0 (305)
Roll inches (mm) 10.0 (254)
CG (face center) up inches (mm) 0.19 (4.8)
CG (face center) to heel inches (mm) 0.06 (1.6)
CG (face center) back inches (mm) 1.38 (35.0)
CG (above ground) inches (mm) 1.38 (35.0)
CG (from shaft axis-toe) inches (mm) 1.73 (44.0)
CG ( shaft axis-back) inches (mm) 0.63 (16.0)
Moment of Inertia (pitch) ounce-in2 (gm-cm2) 13.1 (2400)
Moment of Inertia (yaw) ounce-in2 (gm-cm2) 23.3 (4250)
Moment of Inertia (roll) ounce-in2 (gm-cm2) 21.9 (4000)
Characteristic Time 239 s


Set-up Ball Specifications
Construction: 2-piece
Manufacturer: Bridgestone
Model: "USGA / R&A Calibration"

Parameter Nominal Value
Diameter 1.682" (42.72 mm)
Weight 1.59 oz (45.2 grams)
Ball Compression (Atti) 89
Cover material Surlyn
Cover hardness 60 Shore D
Cover thickness 0.083" (2.1 mm)
Core diameter 1.516" (38.5 mm)
Dimple pattern Quasi-Icosahedron 432
Initial velocity 253.8 fps (77.4 m/s)
COR (rigid block) 0.778 @143.8 fps (43.8 m/s)