26 CFR 48.4071-2 - Determination of weight.
(a) In general - (1) Tires. (i) Metal rims or rim bases are not to be included in determining the total weight of a tire. However, the wire, staples, darts, clips, and other material or fastening devices which form a part of the tire or are required for its use must be included in determining the total weight of the tire. Studs are considered to be part of a tire and are to be included when determining the weight of a tire. In the case of a tubeless tire, the total weight includes the weight of the air valve and stem or any other mechanism that functions as a part of the tire and is used in connection with inflating the tire or maintaining its air pressure.
(ii) When tires are sold with metal rims or rim bases attached, the manufacturer must maintain records that will establish what portion of the total weight of the finished product represents the tire exclusive of the metal rim or rim base.
(2) Inner tubes. The total weight of an inner tube includes the weight of the air valve and stem or any other mechanism attached to the inner tube that is used in connection with inflating the tube or maintaining its air pressure.
(b) Alternative method of determining weight of tires after December 31, 1983. A manufacturer who has received permission from the Commissioner may, subject to such conditions as the Commissioner may prescribe, determine total weight of tires manufactured and sold by the manufacturer on the basis of the average weight for each type, size, grade, and classification. The average weights must be established in accordance with the method approved by the Commissioner and apply for such periods as the Commissioner may prescribe. The Commissioner may terminate the approval granted any manufacturer. In the case of the termination of the approval granted any manufacturer, the termination becomes effective 10 days from the date of the receipt by the manufacturer of the notice of termination. A manufacturer may effect termination, as of a specified date, of the privilege to determine total weight in accordance with provisions of this paragraph by giving no less than 10 days written notice of such intention to the Commissioner. The termination of the approval given a manufacturer does not affect a manufacturer's tax liability for tires sold prior to the effective date of the notice of termination.