The USGA sent a memo, obtained by Golf World, to manufacturers on Thursday, announcing a proposal to limit moment of inertia in drivers. If adopted, the proposal -- which covers driving clubs only -- will go into effect March 1, 2006.
In simplest terms, MOI relates to a clubhead's resistance to twisting on off-center hits. A club with a high moment of inertia can be said to be more forgiving of hits away from the center of the face. In a March 30 notice to manufacturers, the USGA noted that the moment of inertia in driver heads had approximately tripled since 1990. That notice said that going forward the USGA would be looking at three areas of equipment: spin generation, moment of inertia and the adjustability of woods and irons.
Under the proposal, driving clubs would be limited to an MOI of 4,750 gm-cm squared for the MOI around the vertical axis through the clubhead center of gravity, plus a tolerance of 50.
"Research conducted by the USGA has shown that the clubhead size limitations already in place will not effectively prevent increases in clubhead MOI beyond the levels achieved by clubs which were submitted to the USGA prior to March 2005," the notice said. "The USGA has allowed substantial increases in MOI, but it now believes that a limit is appropriate."
In March the USGA said it was "concerned that any further increases in clubhead moment of inertia may reduce the challenge of the game." The primary concern is the potential development of a strong, lightweight material that would allow for 460cc drivers with an incredible amount of free weight to move around, providing a super-high MOI.
"We had thought maybe clubs had reached a natural limit on MOI with the head size of 460cc, but with further research and analysis we came to a different conclusion," said USGA senior technical director Dick Rugge.
Most large-headed drivers currently on the market are in the 4,000 to 4,300 MOI range. Yet when asked if anything had come across his desk that either exceeded or bumped up against the proposed limit, Rugge would only say that "we don't discuss individual submissions. And I don't know what exists in the labs of individual manufacturers. This is based on our own research and modeling of what could happen. And that showed that manufacturers could respect the head size limit but produce clubs with a significantly higher MOI, and we felt it better to act well prior than after the fact."
Rugge said the concern was both distance and forgiveness driven, a point made in the communiqué to manufacturers when it stated, "further increases in MOI could reduce the challenge of the game by reducing the skill required to hit the ball straight. In addition, that could also result in an increase in average driving distance by reducing the likelihood that swinging faster will produce a poor result."
Although the proposed test protocol calls for only one MOI measurement (there are four primary MOI measures), Rugge said the MOI around the vertical axis through the clubhead center of gravity is "the one we believe to be the most critical as it relates to forgiveness, and our research shows that limiting this area of MOI should be adequate. If we find otherwise through our data collecting process, we may revisit it."
And what about the manufacturers who now may have one more area for design improvement limited? "Our primary concern is to do what's good for the game of golf," Rugge said. "We want to be considerate of the needs of the manufacturing community, and take their needs into account, but we always need to think first about what is best for the game."
Representatives from several major equipment companies either could not be reached for comment or declined to comment at this time. The USGA has asked that all written comments on it proposal to be submitted by Nov. 30, 2005.
E. Michael Johnson is the equipment editor of Golf World magazine