RBC Heritage

Harbour Town Golf Links


New Looks: Irons MOI

By Mike Stachura Photos by Jim Herity
March 13, 2008

High moment of inertia (the tendency for a clubhead to remain stable on off-center hits) has been a buzz phrase for drivers, but does high MOI play a role in irons as well?

"High," of course, is relative. Ping's old Eye2 irons, introduced in 1983, featured an above average MOI (about 2,600 grams-centimeters squared), and that number is only slightly below where the typical cavity-back iron is today. Says Benoit Vincent, TaylorMade's chief technical officer: "Unusual materials and shapes might produce an MOI of more than 2,800 in an iron, but in the end, what are the real benefits?"

Stability is good, but high MOI doesn't guarantee playability. "We don't try to maximize one variable at the expense of another," says Alan Hocknell, vice president for innovation and advanced design at Callaway. "For game-improvement irons, center-of-gravity location is our primary design goal. We won't compromise that for the sake of an extra 50 or 100 grams-centimeters squared MOI." Ping design engineer Brad Schweigert notes that a thinner face can help achieve a higher MOI (by redistributing the saved weight to the perimeter), but it also might mean hot spots that could hurt distance control. "Missing the green long is no better than missing it left or right," he says.

Some irons (Nike Sumo², the Nicklaus Polarity MTR and the Adams hybrid-like A3 OS) have moved near the 3,000 MOI range, but the challenge is to do so carefully. "If you increased MOI just by lengthening the blade," says Clay Long, designer of the Polarity, "you increase the slice bias, and that's not what you want from any club."