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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Proposed Rules
139 does not specify the surface type specified within ASTM F1805 for testing.
NHTSA interprets that the medium pack snow condition was intended for use by manufacturers for marketing tires as snow tires. NHTSA seeks comment on whether this assumption is correct.
It is the surface type specified for severe snow tires in UNECE Regulation No.
117 for determining when use of the Alpine or Three-Peak Mountain Snowflake marking that indicates that a tire meets the requirements for use in severe snow conditions. Based upon the research on the SRTT, the 2020 revision of ASTM F1805 contains a revised tractive coefficient range for medium pack snow using the 14-inch SRTT
from 0.250.41 to 0.250.38 and adds a tractive coefficient range for medium pack snow using the 16-inch SRTT of 0.230.38.
Based on the research by ASTM
International and USTMAs recent guidance, NHTSA is proposing to update the definition of a snow tire:
1 To replace the reference to the 14inch SRTT with the 16-inch SRTT and to change the minimum traction index in order to meet the definition of a snow tire from 110 to 112 using this tire; 2 to specify that this traction index is obtained when tested on the medium pack snow surface, and 3 to update the incorporation by reference of ASTM F1805 from the 2000 version to the 2020 version, which is the latest version. ASTM F180520 incorporates the research discussed above. NHTSA is not aware of other research on equivalent performance of the 14-inch SRTT and 16-inch SRTT on snowcovered surfaces other than the testing by ASTM International.

B. Proposed UTQGS Amendments In anticipation of Michelins decision to cease production of the 14-inch SRTT, NHTSA began including testing of the 16-inch SRTT as part of its BCWR
determination. Since the second quarter of 2016, NHTSA has been duplicating BCWR testing using both the 14-inch SRTT and the 16-inch SRTT. NHTSA
has shared some data from this testing with its testing partners named at the end of Section I of this preamble in order to develop options that could be implemented once production of the 14inch SRTT has ended. Four options have been considered:
1. Use the research data to develop a correlation formula between the 14-inch SRTT and the 16-inch SRTT. While this would allow future testing and rating to be based on either SRTT, it was likely to be the most resource-intensive to develop and validate a formula.
2. Establish an effective date for the 16-inch SRTT and begin publishing the quarterly BCWR after that date using four quarters of data using that tire.
After two quarters of testing it was apparent that this was likely to result in a shift in the BCWR. However, large shifts in BCWR have occurred in the past, such as when repaving was done on portions of the route.
3. Allow a transition period in which NHTSA would publish BCWR rates for both SRTTs, allowing manufacturers to choose when to shift within that period.
4. Establish an effective date to begin quarterly testing with the 16-inch SRTT, but continue to calculate the BCWR rate using the prior quarterly testing results used to calculate prior BCWR rates. The first quarter with official testing using the 16-inch SRTT CMT would result in a BCWR rate calculated from the average
of those results and the results of the previous three quarters testing using the 14-inch SRTT CMT, the second quarter would average two quarters with the 16inch SRTT CMT and 2 quarters with the 14-inch SRTT CMT, and so on.
In 2017, Michelin informed NHTSA
that the test results from the first two quarters of testing were within the normal variability seen for BCWR.17
Michelin believed that NHTSA could develop an entirely new formula for determining BCWR, but believed that such a formula may not be able to be developed prior to the end of production of 14-inch SRTT. Instead, Michelin recommended adding a new conversion factor to the existing formula derived from the ratio of the BCWR from the 14-inch SRTT CMT to the BCWR of the 16-inch SRTT CMT measured over a specific number of quarters of testing.
Michelin recommended that this factor be based on at least six quarters of testing, which was all the testing that was available at the time of Michelins recommendation.
NHTSA now has 14 consecutive quarters of testing data. Table 1
summarizes the quarterly BCWR values determined by NHTSA since the first quarter of 2017. As shown in Table 1, NHTSA has determined BCWR
reference values for the 16-inch SRTT.
Table 1 also shows BCWR rates for the 16-inch SRTT beginning in Q2 2017
after four quarters of BCWR values were obtained. Table 1 also shows a conversion factor based on the ratio of the BCWR using the 14-inch SRTT to the BCWR using the 16-inch SRTT
measured over all available quarters of testing.

TABLE 1QUARTERLY BCWR DATA SINCE APRIL 2016

khammond on DSKJM1Z7X2PROD with PROPOSALS

14-inch SRTT
BCWR data
JanuaryMarch 2017
AprilJune 2017
JulySeptember 2017
OctoberDecember 2017
JanuaryMarch 2018
AprilJune 2018
JulySeptember 2018
OctoberDecember 2018
JanuaryMarch 2019
AprilJune 2019
JulySeptember 2019
OctoberDecember 2019
JanuaryMarch 2020
AprilJune 2020

16-inch SRTT
BCWR data
8.090
7.556
9.640
8.932
7.481
8.253
9.648
8.867
6.555
8.242
7.243
7.237
7.695
6.719

5.349
5.952
6.189
6.578
5.731
6.074
6.467
6.602
5.999
5.506
5.656
6.206
5.259
5.616

Quarterly published BCWR rate 9.059
8.573
8.692
8.555
8.402
8.577
8.579
8.562
8.331
8.328
7.727
7.319
7.604
7.224

Theoretical 16-inch SRTT BCWR rate
Derived conversion factor based on prior six quarters

6.017
6.113
6.143
6.213
6.219
6.286
6.144
5.941
5.842
5.657
5.684

1.392
1.393
1.403
1.328
1.348
1.344
1.312
1.301
1.276

17 Michelin presentation; UTQG Wear Change from 14 TO 16 SRTT First Two Test Quarters. See docket No. NHTSA20200067.

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