Federal Register - August 5, 2021
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Source: Federal Register
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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Proposed Rules TABLE 1QUARTERLY BCWR DATA SINCE APRIL 2016Continued 14-inch SRTT
BCWR data
JulySeptember 2020
OctoberDecember 2020
JanuaryMarch 2021
16-inch SRTT
BCWR data
6.983
8.122
7.228
The conversion factor listed in the last column of Table 1 is determined by dividing the average of six quarters of BCWR testing with the 14-inch SRTT by the average of the same six quarters of BCWR with the 16-inch SRTT. The conversion factor is similar for all quarters currently available. NHTSA
requests comments on how the new conversion factor should be selected from among the available quarters of
Quarterly published BCWR rate
6.856
6.886
4.687
Theoretical 16-inch SRTT BCWR rate
7.159
7.380
7.263
data. For example, NHTSA could use the last six or some other number of quarters of data, or all data available to determine the conversion factor.
NHTSA requests comments on which of these possible conversion factors NHTSA could use and why.
For this NPRM, NHTSA is basing the adjustment on the average of all 17
consecutive quarters of available data.
The average BCWR wear rate using the
Derived conversion factor based on prior six quarters
5.984
6.154
6.011
1.257
1.206
1.239
14-inch SRTT is 7.911. The average BCWR wear rate using the 16-inch SRTT
is 5.942. Dividing 7.911 by 5.977 results in a conversion factor of 1.324. Based upon this new conversion factor, the new formula for the treadwear grade, assuming the decision was to use the most recent quarters conversion factor, would be: 18
BILLING CODE 491059P
Projected mileage x base course wear rate 14
P=------------------402
Projected mileage x base course wear rate 16 base course wear rate 14
P=---------------x 402
base course wear rate 16
base course wear rate 14
base course wear rate 16
Conversion Factor = - - - - - - - - - - = 1.324
P
Projected mileage x base course wear rate =- - - - - - - - - - - - - - x 1.324
402
Projected mileage x base course wear rate
P=------------------304
NHTSA does not believe the calculation of projected mileage as used in this formula also requires adjustment, as the calculation takes into consideration the actual measurement of the CMT used during the test of the candidate tire being evaluated.
NHTSA is also proposing to modify language in the treadwear test procedure in 575.104 to reference the total
distance and schedule of events in terms of circuits completed rather than mileage. This proposed change is intended to allow testing to be more flexible in the vent of route changes or other unforeseen circumstances. With the added flexibility of these changes, NHTSA believes that it is preferable to use the actual mileage of the completed circuit in the calculation of the wear rate rather than the estimated 400 miles
per circuit. NHTSA believes that this would ensure that the wear rate reflects the actual mileage covered if the completed 16 circuits is not exactly 6,400 miles. NHTSA seeks comment on these proposed changes and any potential effects they may have on the testing process or data integrity.
NHTSA also seeks comment on the specification in the note to 575.104e2ixC that the CMT must
18 The first equation definition P is set forth in 49
CFR 57.104e2ixF.
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BILLING CODE 491059C
