(a)
Physical dimensions. Tire physical dimensions shall be
determined under uniform ambient conditions as follows:
(1) Mount the tire on a test rim having the
test rim width specified in Appendix A of this chapter for that tire size
designation and inflate it to the applicable pressure specified in Table III of
Appendix A.
(2) Condition it at
ambient room temperature for at least 24 hours.
(3) Readjust pressure to that specified in
paragraph (1).
(4) Caliper the
section width and overall width at six points approximately equally spaced
around the tire circumference.
(5)
Record the average of these measurements as the section width and overall
width, respectively.
(6) Determine
tire outer diameter by measuring the maximum circumference of the tire and
dividing this dimension by pi (3.14).
(b)
Tubeless tire bead unseating
resistance. Bead unseating resistance shall be tested as follows:
(1)
Preparation of tire-wheel
assembly. The tire-wheel assembly shall be prepared as follows:
(i) Wash the tire, dry it at the beads, and
mount it without lubrication or adhesives on a clean, painted test
rim.
(ii) Inflate it to the
applicable pressure specified in Table III of Appendix A of this chapter at
ambient room temperature.
(iii)
Mount the wheel and tire in the fixture shown in Figure 1 of this section, and
force the standard block shown in Figure 2 of this section, against the tire
sidewall as required by the geometry of the fixture.
Click
to view image
(2)
Test procedure. The test
procedure shall be as follows:
(i) Apply a
load through the block to the tire outer sidewall at the distance specified in
Figure 1 of this section for the applicable wheel size at a rate of two inches
per minute, with the load arm substantially parallel to the tire and rim
assembly at the time of engagement.
(ii) Increase the load until the bead unseats
or the applicable value specified in §
159.4(b)(2)(iii)
(relating to requirements) is reached.
(iii) Repeat the test at least four places
equally spaced around the tire circumference.
(c)
Tire strength. Tire
strength shall be tested as follows:
(1)
Preparation of tire. The tire shall be prepared as follows:
(i) mount the tire on a test rim and inflate
it to the applicable pressure specified in Table III of Appendix A of this
chapter;
(ii) condition it at room
temperature for at least three hours; and
(iii) readjust its pressure to that specified
in subparagraph (i).
(2)
Test procedure. The test procedure shall be as follows:
(i) Force a 3/4-inch diameter cylindrical
steel plunger with a hemispherical end perpendicularly into the tread rib as
near to the centerline as possible, avoiding penetration into the tread groove,
at the rate of two inches per minute.
(ii) Record the force and penetration at five
test points equally spaced around the circumference of the tire. If the tire
fails to break before the plunger is stopped by reaching the rim, record the
force and penetration as the rim is reached and use these values in
subparagraph (iii).
(iii) Compute
the breaking energy for each test point by means of the following formula:
W =Energy, inch-pounds;
F =Force, pounds; and
P =Penetration, inches.
(iv) Determine the breaking energy
value for the tire by computing the average of the five values obtained in
accordance with subparagraph (iii) of this paragraph.
(d)
Tire
endurance. Endurance shall be tested as follows:
(1)
Preparation of tire. The
tire shall be prepared as follows:
(i) Mount a
new tire on a test rim and inflate it to the applicable pressure specified in
Table III of Appendix A.
(ii)
Condition the tire assembly to 100°F plus or minus 5°F for at least
three hours.
(iii) Readjust tire
pressure to that specified in subparagraph (i) immediately before
testing.
(2)
Test
procedure. The test procedure shall be as follows:
(i) Mount the tire and wheel assembly on a
test axle and press it against a flat-faced steel test wheel 67.23 inches in
diameter and at least as wide as the section width of the tire to be tested or
an approved equivalent test wheel, with the applicable test load specified in
Table I of Appendix A for the size designation, type, and maximum permissible
inflation pressure of the tire.
(ii) During the test, the air surrounding the
test area shall be 100°F plus or minus 5°F.
(iii) Conduct the test at 50 miles per hour
in accordance with the following schedule without pressure adjustment or other
interruptions:
Maximum permissible inflation
pressure
|
Loads for
-
|
4 hours
|
6 hours
|
24 hours
|
Loads from table I
(listed inspecified psi or KPa column)
|
32
psi....................................
|
24
|
28
|
32
|
36 psi
...................................
|
28
|
32
|
36
|
40 psi
...................................
|
32
|
36
|
40
|
240 KPa
..............................
|
180
|
220
|
240
|
280
KPa...............................
|
220
|
260
|
280
|
300 KPa
..............................
|
180
|
220
|
240
|
Load as specified
percentage of maximum load rating marked on tire sidewall
|
60 psi
...................................
|
85
|
92
|
100
|
(iv) Immediately after running the tire the
required time, measure its inflation pressure. Allow the tire to cool for one
hour. Then deflate the tire, remove it from the test rim, and inspect it for
the conditions specified in §
159.4(b)(2)(v)(A)
(relating to requirements).
(e)
High speed performance.
High speed performance shall be tested as follows:
(1) After preparing the tire in accordance
with subsection (d)(1), mount the tire and wheel assembly in accordance with
subsection (d)(2)(i) and press it against the test wheel with the load
specified in Table I of Appendix A for the size designation of the tire and the
applicable pressure specified in Column B of the following table:
A
|
B
|
Maximum permissible inflation
pressure
|
Load from Table I
|
32 psi .....................................
|
24
|
36 psi .....................................
|
28
|
40 psi .....................................
|
32
|
240 KPa ................................
|
180 KPa column.
|
280 KPa ................................
|
220 KPa column.
|
300 KPa ................................
|
180 KPa column.
|
Load as specified percentage of maximum
load rating marked on tire sidewall
|
60 psi
....................................
|
85
|
(2) Break in the tire by running it for two
hours at 50 miles per hour.
(3)
Allow to cool to 100°F plus or minus 5°F and readjust the inflation
pressure to the applicable pressure specified in Table III of Appendix A of
this chapter.
(4) Without
readjusting inflation pressure, test at 75 miles per hour for 30 minutes, 80
miles per hour for 30 minutes, and 85 miles per hour for 30 minutes.
(5) Immediately after running the tire the
required time, measure its inflation pressure. Allow the tire to cool for one
hour. Then deflate the tire, remove it from the test rim, and inspect it for
the conditions specified in § 159.4(b)(2)(v)(A).