Remember when we ran out of phone numbers? The growth of credit card readers, fax machines, cellphones and the Internet ate up existing number combinations needed for phone numbers within area codes, forcing the government to start splitting existing area codes into smaller re-numbered geographic sections.

The same thing has apparently happened with tire identification numbers. With the growth of overseas makers wishing to enter the North American market, we have nearly run out of TINs – sort of.

NHTSA yesterday posted a new proposed rule that would expand the manufacturer identifier portion of the TIN from two digits to three. This would “substantially increase the number of unique combinations of characters that can be used to identify individual manufacturers of new tires.”

In addition, NHTSA has proposed to standardize the length of TINs to 13 characters for new tires and seven for retreads, which it feels would “eliminate confusion that could arise from the variable length of tire identification numbers.”

TINs were established in 1971 to help consumers, tire sellers and other users to identify “defective or noncompliant tires.” With the advent of FMVSS 139 in 2007, TINs were required on both sidewalls of a tire, again to make it easier for owners to find recalled tires.

From its adoption in 1971, the TIN has consisted of up to four groups of characters. The first group identifies the manufacturer of the tire. Each tire plant has its own unique identifier. The second and third groupings provide information about the tire itself, including size or “any other significant characteristics of the tire.”

The fourth group is the date code, identifying the week and year during that particular tire was manufactured. Although this code was originally three characters, it was later expanded to four.

Still, the length of a TIN is not currently standardized. Partial TINs are allowed on one side of the tire, but this is not well understood by consumers. With all of the possible variations in TIN length allowed, a full TIN for new tires may be anywhere between eight and 13 characters. This variation has apparently confused tire owners looking to identify their tires for recall purposes.

“By standardizing the length of the TIN, there will be no confusion that a nine-symbol TIN is a partial TIN and a 13-symbol TIN is a full TIN,” NHSTA said. “This NPRM would make the new standardized length TIN mandatory for manufacturers using a three-symbol plant code. Manufacturers who have previously been assigned a two-symbol plant code may continue to use the existing TIN grouping requirements (including the use of the optional codes) until they begin using a three-symbol plant code. This will allow manufacturers to begin using both the three-symbol plant code and the 13-symbol TIN at the same time.”

NHTSA proposes that the new rules be implemented immediately, except it is allowing a five-year period for complete compliance so that tiremakers would not be forced to change molds before their lifecycle ends.

The agency is accepting comments for 30 days from today, but no timetable for consideration or decision-making was stated.