Interpretation ID: nht70-1.12
DATE: 10/29/70
FROM: AUTHOR UNAVAILABLE; R. H. Compton; NHTSA
TO: Atlas Supply Company
TITLE: FMVSS INTERPRETATION
TEXT: Reference is made to your letter of October 8, 1970, requesting an increase in the maximum permissable overall width of the "78" series belted bias passenger car tires covered by Table I-J, Appendix A, of MVSS 109.
The dimensional requirements specified in MVSS 109 for passenger car tires are the result of a rule making action in which the tire industry and other interested persons participated. Tire section width and overall width were permitted to exceed the specified section width dimensions by 7% to accommodate differences in manufacturing tolerances, design practice, tire growth patterns when inflated, and to provide for sidewall decorations and protective ribs.
The allowance of 7% is considered the maximum desirable for dimensional uniformity and interchangeability among tires of the same size produced by different manufacturers. For this reason, we cannot give favourable consideration to your request at this time.