WHAT YOU NEED TO KNOW: The three new Mizuno ST230 drivers make a big push forward towards improving ball speed and optimising launch conditions with a lot of light carbon composite and a little bit of heavy steel.

The key is a five-gram bar of steel encased in polyurethane-filled cut through slot in the front of the sole of these drivers. The steel lowers the centre of gravity while the opening allows better flexing of the face.

The STZ-230 uses the rest of the saved weight from in the centre rear perimeter for maximum stability. The STX-230 pushes that extra mass towards the rear and heel side for increased workability and a slight draw bias.

The STX-230 PLTNM uses a lighter overall construction (by 30 grams) to provide more potential swing speed for moderate speed players.


PRICE: STZ-230 ($999): 9.5, 10.5 degrees; STX-230 ($999): 9.5, 10.5, 12 degrees; STX-230 PLTNM (TBC): 10.5, 12 degrees. Available in February.


1. Forward thinking. You can talk forever about any number of material attributes behind the latest drivers, but the simple truth is they’re all largely on this quest to do two things: Maximise ball speed and minimise spin.

In practical terms, to do the former you have to figure out some way to make the face propel the ball better, while to accomplish the latter, you have to find a way to lower the centre of gravity, usually by pushing weight forward. The team at Mizuno believes they’ve found a way to accomplish both by doing one thing. That one thing is a five-gram bar of steel.


Maybe that doesn’t sound like much, but it’s all about where it’s placed. With a cut-through opening in the front of the sole, the new Mizuno ST-230 drivers create a more flexible face. But when you fill that opening with a flexible polyurethane and then embed that heavy steel weight within that polymer, you get it all, said , director of research and development for Mizuno.

“By placing this weight low and forward in this polymer, we were able to get the effect we want, more ball speed and a nice reduction in spin, with a minimal amount of weight,” he said of the “CORTECH Chamber,” what the company calls that region in the sole. “It really gave us another lever to pull. Remember the idea is to reduce spin, add speed and maintain stability.”


That last idea is not trivial. While it’s certainly possible to have put more weight forward, it would have come at the expense of having less weight to push to the perimeter. That extra available mass is made possible by a large carbon composite crown and sole sections. It’s able to be redistributed to the deep centre on the STZ-230 and slightly towards the rear heel on the STX-230 and STX-230 PLTNM. By having another 14 grams that can go to those perimeter sections, the ST230 drivers maintain high forgiveness on off-centre hits, Llewellyn said.

The polymer also plays a role in increasing ball speed. Its flexibility allows the sole to flex more, which contributes to better ball speed lower on the face. Meanwhile, at impact, “the weight itself adds momentum to the way the face is flexing,” Llewellyn said. In other words, the weight and the polymer together are creating both more speed and less spin.


2. Face facts. Not to be overlooked in all this speed talk is the makeup of the faces on the ST230 drivers. As it has in the recent past, these drivers use 2041 Beta Titanium, which helps produce a face with variable thicknesses that increase performance on mis-hits, Llewellyn said.

“It allows us to be very aggressive in terms of a multiple thickness face design,” he said. “And Beta Titanium has a faster strain rate recovery so it can snap back faster than other titanium alloys.”

3. Draw bias isn’t just for slicers anymore. Perhaps the most interesting development in the three Mizuno drivers is how the so-called draw bias version might just find its way into the bags of elite players. Certainly the STZ-230 with its high forgiveness and neutral to slight fade bias might be the first options for better players, but Mizuno’s testing with better players has shown that the slightly heel-biased STX-230 is resonating with some better players because the centre of gravity is closer to the shaft.


“ST-X 230 is a complex character,” said Chris Voshall, Mizuno’s director of product. “Although in the higher loft option it’s a higher flying draw-biased option, the 9.5 for many of our tour players was more workable and faster from the face.”