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Interpretation ID: nht71-1.33

DATE: 04/20/71

FROM: AUTHOR UNAVAILABLE; Francis Armstrong; NHTSA

TO: WARREN M. BARNETT

TITLE: FMVSR INTERPRETATION

TEXT: This is in reply to your letter of February 23, 1971, requesting advice on the acceptability of your regrooving pattern for regrooved tires.

Enclosed is a copy of the Rules and Regulations on regrooved and regroovable tires as it appears in the Federal Register published January 24, 1969, under Section 369.7(a)(1) Requirements, "After regrooving, the new grooves generated into the tread material and any residual original molded tread groove which is at or below the new regrooved groove depth, shall have a (Illegible Word) of 90 linear inches of tread edges per linear foot of tire circumference."

There are no measurements on your drawings to assist us in determining if your zig-zag grooves and the three circumferencial grooves measure 90 linear inches. Three straight circumferential grooves would only provide approximately 72 linear inches.

The use of lateral cuts should substantially increase the tread edge measurements; providing the lateral cuts are from shoulder to shoulder to allow unobstructed fluid escape passages as required in Section 369.7(a)(5).

Thank you for your interest in tire safety.

Enclosure