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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Proposed Rules Initial testing confirmed the assumption that using the 16-inch SRTT
resulted in a test surface having a higher PFC than when evaluated using the 14inch SRTT. Transportation Research Center, Inc. TRC conducted initial testing in support of the ASTM
committee evaluating this issue the E17.21 committee.11 Testing was conducted on 15 different surfaces of varying friction. The evaluation of a dry test surface e.g., 0.9 PFC using the 14inch SRTT using the 16-inch SRTT
resulted in a PFC over 15 percent higher than the PFC derived using the 14-inch SRTT. However, testing on a low
friction surface 0.5 PFC using the 14inch SRTT showed that the PFC
derived using the 16-inch SRTT and the 14-inch SRTT was similar.
Because the difference in performance between the 16-inch SRTT and the 14inch SRTT was not consistent for all levels of surface friction, something more than a simple multiplier is necessary to correlate performance between the two tires. ASTM
International has developed such a formula. That formula is included in the 2019 update to ASTM E1337, which NHTSA is proposing to incorporate by reference into the FMVSSs, in place of
the 1990 version of E1337 currently referenced. NHTSA has used the formula in the 2019 version of E1337 to derive PFC value for all of the FMVSSs.
Those values are listed in the table below.
Each value derived using the formula was rounded to the hundredths position, rounding up if necessary. This ensures that the updated FMVSS test surface PFC specification will be no more stringent as a result of this proposed amendment than it is now, consistent with NHTSAs intent in this rulemaking.

FMVSS section FMVSS
FMVSS
FMVSS
FMVSS
FMVSS
FMVSS
FMVSS
FMVSS
FMVSS
FMVSS
FMVSS

No.
No.
No.
No.
No.
No.
No.
No.
No.
No.
No.

khammond on DSKJM1Z7X2PROD with PROPOSALS

PFC value using 14-inch SRTT

PFC value using 16-inch SRTT

0.9
0.5
0.9
0.5
0.9
0.45
0.8
0.9
0.9
0.9
0.9

1.02
0.55
1.02
0.55
1.02
0.50
0.90
1.02
1.02
1.02
1.02

105 S6.9.2a high friction testing
105 S6.9.2b low friction testing
121 S5.3.1.1, S5.7.1, S6.1.7 high friction testing 12
121 S5.3.6.1, S6.1.7 low friction testing
122 S6.1.1.1 high friction testing
122 S6.1.1.2 low friction testing
122 S6.9.7.1
126 S6.2.2
135 S6.2.1, S7.4.3, S7.5.2, S7.6.2, S7.7.3, S7.8.2, S7.9.2, S7.10.3, S7.11.3
136
500 13

NHTSA commissioned confirmatory testing using the 16-inch SRTT to verify that the PFC values discussed above are equivalent to the PFC values in the FMVSSs derived using the 14-inch SRTT. NHTSA has contracted with TRC
to conduct this testing on five different test surfaces wet ceramic, wet jennite, wet asphalt, dry asphalt, and dry broomed concrete. These test surfaces range from high to low PFC values. For each test surface, 10 of each of the 14inch SRTT and the 16-inch SRTT were each tested 3 times with 10 stops per test, for a total of 300 tests for each size SRTT on each test surface. A final report summarizing the results has been placed in the docket identified at the beginning of this NPRM.
2. Snow Tire Definition Presently, for a manufacturer to designate a tire as a snow tire, the tire must attain a traction index equal to or greater than 110 compared to the 14inch SRTT when tested using the snow traction test in the 2000 version of ASTM F1805. The ASTM F09
committee on tires commissioned a study to determine the feasibility of 11 See
docket No. NHTSA20200067.
is also proposing to revise Tables I, II, and IIA in FMVSS No. 121 to eliminate the redundant references to PFC values in those tables.
In place of PFC values, NHTSA is proposing to include in Table I Stopping Sequence references 12 NHTSA

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replacing the 14-inch SRTT with the 16inch SRTT in the determination of whether a tire meets the definition of snow tire. This study was funded by the United States Tire Manufacturers Association USTMA.
The study consisted of testing of traction during the winter test seasons of 2016, 2017, and 2018 to develop a method to correlate results of tests conducted using the 16-inch SRTT with those conducted using the 14-inch SRTT. ASTM International has published a technical report documenting this work.14 ASTM
International determined that a correlation factor of 0.9876 was appropriate, meaning that a tire that attained a rating of 110 when tested using the 14-inch SRTT correlated to a rating of 111.4 or 111.5 when tested using the 16-inch SRTT, depending on the number of significant digits considered. Recent guidance issued by the USTMA, a trade association consisting of companies that manufacture tires in the United States, recommends a minimum traction index of 112 using the 16-inch SRTT.15

Accordingly, NHTSA is proposing to amend the definition of snow tire in FMVSS No. 139 to specify that a snow tire is a tire that attains a traction index of 112 when tested using the updated F1895 test method using the 16-inch SRTT. This proposal is consistent with the guidance issued by USTMA, which NHTSA believes reflects a consensus within the tire industry on the appropriate traction index for use in determining what qualifies as a snow tire. NHTSA seeks comment on this proposal.
Furthermore, after reviewing this information from the USTMA, NHTSA
determined that additional clarification was necessary to the definition of a snow tire in FMVSS No. 139. The latest 2020 version of ASTM F1805
defines the standard test procedure for measuring traction on snow and ice surfaces. However, there are multiple surface types in both the snow and ice categories. They include soft pack new snow, medium pack snow, medium hard pack snow, hard pack snow, icewet, and icedry.16 The definition of snow tire in FMVSS No.

to the sections in which the various procedures are set forth, which is a more helpful reference.
13 Although FMVSS No. 500 specifies a PFC value for the test surface, the test surface is only used to verify the vehicles maximum speed.
14 Available at https www.astm.org/COMMIT/
2019_04_10_E1136%20to%20

F2493%20transition%20for%20ASTMF1805.pdf last accessed April 13, 2021.
15 See https www.ustires.org/sites/default/files/
USTMA_TISB_37_0.pdf last accessed April 13, 2021.
16 The surface types are defined in the text of ASTM F1805.

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