ASTM F1881-98
(Test Method)Standard Test Method for Measuring Baseball Bat Performance Factor
Standard Test Method for Measuring Baseball Bat Performance Factor
SCOPE
1.1 This specification defines a method for determining bat performance by measuring the Coefficient of Restitution (COR) of the bat-ball collision using a ball with a known COR then deriving a bat performance factor.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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An American National Standard
Designation: F 1881 – 98
Standard Test Method for
Measuring Baseball Bat Performance Factor
This standard is issued under the fixed designation F 1881; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.7 moment of inertia (MOI), n—a measure of mass
distribution relative to an axis of rotation. It is the product of
1.1 This specification defines a method for determining bat
the mass multiplied by the square of the distance to the mass,
performance by measuring the Coefficient of Restitution
summed over the entire bat.
(COR) of the bat-ball collision using a ball with a known COR
3.1.8 period, n—the time required for a pendulum to oscil-
then deriving a bat performance factor.
late through one complete cycle.
1.2 This standard does not purport to address all the safety
concerns, if any, associated with its use. It is the responsibility
4. Significance and Use
of the user of this standard to establish appropriate safety and
4.1 This test method offers a laboratory means to compare
health practices and to determine the applicability of regula-
the overall performance of a bat as it relates to batted-balls
tory limitations prior to use.
speeds.
2. Referenced Documents 4.2 Use of this test method can provide sports governing
bodies a means to compare the anticipated batted-ball speed,
2.1 ASTM Standards:
thus batted-ball distance for the purposes of controlling the
F 1887 Test Method for Measuring the Coefficient of Res-
game and safety.
titution (COR) of Baseballs and Softballs
4.3 Batted-ball speed can be related to bat performance
F 1888 Test Method for Compression-Displacement of
factor (BPF) using the following formula:
Baseballs and Softballs
w w R 2 a
~ !
3. Terminology k 5 1 (1)
S D S 2 D
W
~I 2 Wa !
3.1 Definitions of Terms Specific to This Standard:
where:
3.1.1 balance point, n—the distance to the center of mass
V = bat swing speed, mph. The speed is
measured from the knob.
measured at the point of impact, at the
3.1.2 bat-ball coeffıcient of restitution (COR), n—the COR
sweet-spot of the bat, otherwise speci-
of a specific ball colliding with a stationary bat as defined in
fied as the COP. Impacts at the COP
this test method. See coeffıcient of restitution (COR).
offer essentially the highest batted-ball
3.1.3 bat performance factor, n—the ratio of performance
speeds due to the optimization of mo-
change a bat introduces to a ball collision, compared to a ball
mentum transfer. The BPF value has
colliding with a solid wall as in the ASTM Ball COR test.
been measured at this point and repre-
3.1.4 center of percussion (COP), n—also known as the
sents the maximum performance of the
center of oscillation, the length of a simple pendulum with the
bat; therefore, the following calcula-
same period. Forces and impacts at this location will not induce
tions are correct only when the bat
reactions at the pivot point.
swing speed at the point impact are
3.1.5 coeffıcient of restitution (COR), n—a measure of
used. The swing speed at the COP can
impact efficiency calculated as the relative speed of the objects
be as much as 20 % slower than bat
after impact divided by the relative speed of the objects before
speeds measured at the end of the bat.
impact.
Typical adult values are 60 mph for
3.1.6 elevated speed, n—ball speeds in excess of the stan-
average players and 70 mph for aver-
dard 88 fps.
age collegiate level ball players. It is
recognized that a players swing speed
This test method is under the jurisdiction of ASTM Committee F-8 on Sports
varies depending on skill level, condi-
Equipment and Facilities and is the direct responsibility of Subcommittee F08.26 on
tioning, and bat swing weight (MOI).
Baseball and Softball Equipment and Facilities.
Current edition approved April 10, 1998. Published September 1998.
Annual Book of ASTM Standards, Vol. 15.07.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F1881–98
method shall be marked with the actual tested and verified ball
v = pitch speed, mph, the horizontal speed
COR when tested in accordance with Test Method F 1887.
of the ball incoming to the batter,
5.2.1.1 Compression—300 to 375 lb at ⁄4-in. deflection
W = bat weight, oz,
w = ball weight, oz, (1335 to 1668 N).
I = MOI, oz-in. ; typical value for an av-
5.2.1.2 Weight—5.0 to 5.25 oz (142 to 149 g).
erage bat is 9 000,
5.2.1.3 Size—9 to 9.5-in. circumference (22.9 to 23.5 cm).
e = bat-ball COR = BPF 3 ball COR. One must chose a
5.2.1.4 COR—0.525 to 0.555.
ball COR to determine the batted ball
5.2.2 Ball Cannon—A device capable of shooting a ball at
speed,
a speed of 88 ft/s with a maximum aiming error of 6 0.125 in.
a = distance from pivot to center of mass
(6 mm) at the point of impact. The ball shall not have a spin
(balance point); typical value is 14 in.,
rate in excess of 50 rpm. Typical pitching machines cannot
R = COP; the radius of rotation typical
yield the aiming accuracy required by this test method. Cannon
value for an average bat is 22 in., and
exhaust air must not be allowed to pass to the bat. The cannon
k = ball-bat inertia ratio, convenient means
shall not blow out a match located in the impact location when
to collect terms. Typical value for the
it is dry-fired (fired without a ball). The ball cannon can be any
average bat is 0.35.
distance from impact location, as long as it can meet the ball
V~1 1 e! 1 v~e 2 k!
aim requirements and provide six valid impacts in 12 shots or
batted ball speed 5 (2)
~1 1 k!
less.
5.2.3 Bat Speed Gate—A light trap, device, or an equiva-
NOTE 1—Ball COR varies with relative impact speed.
lent, capable of measuring an edge traveling at speeds in excess
of 88 ft/s (26.8 m/s) with an accuracy of 0.5 ft/s or better (0.2
5. Apparatus
m/s). The first sensor shall trigger when the bat rotates no less
5.1 Bat Center of Percussion Test Apparatus:
than 15° and no more than 20° from its start position. It is
5.1.1 Ruler, suitable for measuring lengths up to 42 in. to
suggested the second trigger be 3 in. away from the first and
the nearest 0.125 in. (3 mm).
must not be any further than 3.6 in. away in a 6-in. (15.24-cm)
5.1.2 Scale, suitable for measuring weight up to 48 oz (1360
radius.
g) to the nearest 0.1 oz (2.8 g).
5.2.4 Ball Speed Gate—A light trap, device, or an equiva-
5.1.3 Stopwatch, suitable device for measuring time to the
lent, capable of measuring a sphere traveling at speeds in
nearest tenths of seconds (0.1 s).
excess of 88 ft/s (26.8 m/s) with an accuracy of 0.5 ft/s or better
5.1.4 Stand—A frame large enough to allow a bat held in a
(0.2 m/s). The device shall measure across a length of no less
vertical position to swing freely (see Fig. 1).
than half the ball diameter to avoid centering error. For
5.1.5 Collar-Clamp—A light weight clamp or collar that
example, when testing balls, the device shall sense an object
can hold the weight of a bat and provide a fixed pivot location.
across a 2-in. (5-cm) line. The first sensor shall trigger when
Collar shall be rotationally balanced (see Fig. 1). A simple
the ball is no more than 12 in. (30.5 cm) from the bat surface.
hook-loop band used with sharp pointed screw may be used as
It is suggested the second trigger to 3.6 in. away from the first
a pivot.
and must not be any further than 8 in. away.
5.2 Bat-Ball COR Test Apparatus:
5.2.5 Bat Pivot Support—A turntable with clamps to sup-
5.2.1 Test Balls—Official balls approved for play marked
port and align the bat in the path of the ball. The clamp surfaces
with the actual Coefficient of Restitution (COR) from a
shall be a 45° Vee clamp with a radius no greater than 2 in. (5
previously run test. Each individual ball used in this test
cm). The rotating clamp and shaft assembly shall not weigh
more than 6 lb (2.7 kg) and shall spin freely in a pair of ball
bearings (see Fig. 2). The polar Moment of Inertia (MOI) for
the clamp turntable assembly shall not exceed 192 oz/in. (35
117 g/cm ).
6. Determination of Bat Features and Test Location
6.1 Weight—Measure the weight of the bat to the nearest
0.01 oz (0.28 g).
6.2 Balance Point—Measure and record the overall bat
length to the nearest 0.063 in. (2 mm) and overall bat weight as
specified in 6.1. Place bat on balance point stand as shown in
Fig. 3. Adjust height of knob stand to keep bat axis level.
Knowledge of the knob and barrel diameters can be helpful
here. Measure and record the barrel end weight of the bat, and
calculate the balance point of the bat using the following
FIG. 1 MOI Fixture formula:
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