When he hit it, he smiled. The ball flew high, far and straight, maybe too straight for a player who needs to fade it and draw it on the PGA Tour's challenging courses.

Woods believes the Nike SQ Sumo2 could start a revolution in the design of drivers, a club head that for centuries has been made to resemble a circle and was nearly as unstable as a feather in the wind.

"If you're a rocket scientist and a physicist," Woods says, "you wouldn't design the drivers we've been playing."

Hence the latest approach has designs on squares, triangles and ovals. Anything goes.

New designers, many with aerospace and defense backgrounds, have taken over the golf industry and charted a more sophisticated — and pricier — selection of drivers. The goal: to improve moment of inertia (MOI), a measurement of the stability of the club head. The more stable the head, the more accurate the shot, especially on off-center hits.

To achieve that, designers took weight saved by using lighter materials and distributed it as far behind the face of the club as possible. Callaway and Nike and others believe the square design is the best way to maximize the weight's effect.

For equipment companies, the driver is crucial. It is the club that makes the statement for recreational players trying to impress their friends at the first tee. What club the pros use is a huge factor in what the recreational player wants to buy.

Chris McGinley, vice president of marketing for Titleist, says 1.75 million premium drivers, worth $400 million, are sold each year. "They are the big, sexy clubs," he says. "On average, serious amateur golfers buy a set of irons every five years, but they buy a new driver every year."

This new generation of drivers, on display this week at the PGA Merchandise Show in Orlando, is the outcome of limits imposed on the size of the driver head (460 cc) and the bounce of the face by the U.S. Golf Association. Manufacturers couldn't go any bigger — designers are left with a head of 5 inches by 5 inches — so changing the shape was the next step. The new clubs will hit the market in February and March.

Squares and triangles

When Woods earned his first victory about a decade ago, it came against Davis Love III, who was still using a driver head made of wood. In the interim, more aerodynamic golf balls and clubs made of space-age materials such as light, strong and flexible titanium and carbon composites, dominate the industry.

"There are a lot of ways to design a golf club," says Tom Stites, director of product creation for Nike, "but the best way to take advantage of the USGA's rules on drivers is to make (the head) square."

Callaway, which led the titanium revolution with the Great Big Bertha driver in the early 1990s, will introduce the FT-i, a square driver made of metal and carbon composite. Titleist, one of the industry's more traditional companies, will showcase the 907D1, nicknamed "The Tooth" because it's shaped like a triangle. Adams Golf has the Insight BUL (Big, Ugly and Long), square with rounded-off edges, because company executives feared the square design might be too radical for the marketplace.

Nike plans to launch its driver Feb. 3 with "Sumo Saturday," a nationwide promotion. Some locations will have their employees wear sumo wrestling shorts — over their pants, of course. The Callaway FT-i will hit retail stores Feb. 15.

Mark Marney, CEO of The Golf Warehouse, an online store, says he'll sell the Nike Sumo for $399 and the Callaway FT-i for $499, roughly in line with prices for previous launches of new drivers.

"I think the public will buy them," he says. "They are unusual products, and they'll all help you hit the ball straighter."

Nike and Callaway each have Sumo2 and FT-i models with higher loft and softer flexes designed for women. But the new campaigns are geared toward men, who make up 75 percent of the market.

"We're bullish on it," Jeff Colton, Callaway's senior vice president of research and development, says of the square design. "This is not just a gratuitous, odd-shaped driver. It really works. The average golfer will hit the ball straighter."

A prominent dissenter is TaylorMade, which has dominated the PGA Tour and the golf market with a driver design featuring movable weights so players can customize to fit their swings. There are no plans for a square driver but other geometries are under review. "If we thought square was better we'd be all over it," TaylorMade's Sean Toulon says.

Tiger keeps his SasQuatch

Woods, who carries Nike's golf division and could create a market for the Sumo2 by winning with it, has decided to stick with the earlier generation, the SasQuatch, which has a more traditional shape.

"The neat thing about it," Woods says of the Sumo2, "is that you do hit the ball a lot straighter. I was surprised that something that looks (so odd) could perform the way it does."

Hitting it straight isn't always the goal of the touring pro, but it is the Holy Grail for recreational golfers. "If you're a good player like Tiger, you won't be hurt by the physics that's in this club," Stites says. "You just won't be able to take advantage of it."

K.J. Choi, however, embraced the new technology last year. Using the Sumo2, Choi won the Chrysler Championship in October, his fourth career PGA Tour victory. He likes the high, straight ball flight and wasn't bothered by the ringing sound produced by the Sumo2, a noise similar to that of an aluminum bat striking a baseball.

"It took some time to adjust to it," Choi says in an e-mail. "At first the trajectory of the ball seemed a bit high, but with practice I got it under control."

Because precision is so crucial, most pros are slow to accept radical equipment changes. But once they believe it's a better club, easier to hit, they embrace it.

Phil Mickelson has practiced with Callaway's square driver, the FT-i, since last fall but he opened the season last week at the Bob Hope Chrysler Classic playing the company's FT-5, a new design that's more round than square.

"I think it's a revolutionary driver," he says of the FT-i. "Because it's such a drastic change, because the moment of inertia is so high and because the ball goes so straight, it's going to take a little more time for the Tour players to accept it."

He expects to have the FT-i in his bag by April when he returns to Augusta National as defending Masters champion. "If I want to hit it straight I'll go to the FT-i. I'm leaning toward it at Augusta because I need to hit the ball longer there."

Tom Wishon, a club designer who last year wrote the book The Search for the Perfect Driver, says there will be no gray area with this technology. Golfers will "either love it, or they'll hate it."

Chip Brewer, president of Adams Golf, believes physics already has determined the future. "I don't know if the design will be square or triangular or oval, but MOI is clearly the future. And a square has always been more stable than a circle."

The sound of square