• Mizuno announces the ST-Z 230 and ST-X 230 drivers.
  • They feature a speed-enhancing CORETECH chamber.
  • A lightweight ST-X 230 PLTNM model is also available.
  • Retail price is $499 for the standard Z and X and $549 for the PLTNM model.
  • Availability begins Feb. 23.

A photo of Mizuno ST-230 drivers, the ST-Z 230 and ST-X 230

The new Mizuno ST-Z 230 Z and ST-X 230 are part of the company’s ongoing quest to shed its identity as an irons-only brand.

On one hand, it’s not the absolute worst problem to have. The company achieved its highest-ever market share this year and recently it has claimed about 15 percent of the market. It routinely over-indexes among MyGolfSpy readers with more than 20 percent of you reporting that you play Mizuno irons.

That’s good.

The less good?

An image of the ST-Z logo on the Mizuno ST-Z 230 driver

While Mizuno still over-indexes with our readers in the driver category, the 2.4 percent of respondents who play a Mizuno driver are only slightly higher than the real number.

To its credit, Mizuno is staying the course. These days, all Mizuno contract players are required to play Mizuno drivers and, surprisingly, the company sees the occasional bit of non-contract play as well.

There’s a long way to go but Mizuno’s ST driver franchise appears to be moving in the right direction.

Slowing Down a Bit

As you might expect, the plan—or at least the hope—for the ST-230 series is to continue the momentum. To that end, Mizuno has decided to shift driver development to a two-year cycle. I think we all understand that it’s rare that significant progress is made in one year and, by tapping the brakes a bit, Mizuno will be able to make a bigger investment in fitting tools (heads, shafts … that sort of thing).

Who knows? Maybe they’ll also start making more left-handed options available as well.

That’s not to say the Mizuno ST-X 230 and ST-Z 230 will be the only drivers in the family. You can expect a line extension later in the year and most of you can probably guess what that will be. That one will be on a two-year cycle.

With an understanding of Mizuno’s road map, let’s look at where their ST driver franchise stands.

Mizuno ST-230 Drivers – Tech Upgrades

the Mizuno ST-X 230 Driver on a CG gauge.

The two Mizuno ST driver models, the ST-Z 230 and ST-X 230, are the direct replacements for their ST-220 counterparts but that’s not to say everything has changed.

In recent driver iterations, Mizuno has paired its 2041 beta-titanium “CORETECH” face with its WAVE sole design. The purpose of WAVE sole was to absorb deflection in the low-face area. It also helped to expand what Mizuno calls the “COR area” (the area of the face where CT values remain above .80).

Ultimately, it was Mizuno’s method for boosting ball speed while staying within USGA rules.

The ST-Z 230 and ST-X 230 drivers feature a significant evolution in CORETECH. It’s what Mizuno calls the CORETECH Chamber.

but Mizuno has been working towards the CORTECH Chamber for four years. The company says its drivers were already fast but the CORETECH Chamber was the missing piece that will unlock even faster ball speeds.

In its physical manifestation, the CORETECH Chamber is comprised of a small steel I-beam suspended in what looks like blue raspberry Jell-O. The realities are a bit more technical. The blue stuff is actually an elastomeric polymer (responsive material) that’s necessary, in part, because steel can’t be welded directly to titanium.

How Mizuno’s CORETECH Chamber Works

a closeup of the speed enhancing coretech chamber on the Mizuno ST-230 Drivers

The CORETECH Chamber is a through-slot design. That allows the sole to flex and, because the new TPU construction is less rigid and reduces stress on the face, Mizuno was able to thin things out a bit to get some additional speed out of low-face impacts.

The TPU material also has sound-dampening qualities so you should expect Mizuno ST-230 drivers to have a more muted, modern sound compared to prior models.

The most intriguing part of Mizuno’s CORETECH Chamber design is what happens at impact. The material in the CORETECH Chamber comes out of compression faster than the face. That gives you something of an acceleration effect as the steel rebounds against the face.

It’s an impressive bit of five-star innovation that is perhaps unexpected from Mizuno. That’s not to say the company is claiming it has shattered existing performance boundaries.

Speed gains average out to a little over half a mile an hour faster across the board than without the steel insert. Also of note, because the steel is forwardly placed, spin rates drop by about 200-250 rpm.

As you know, more speed and lower spin almost always ends in more distance.

Beta Titanium Face

A closeup of the beta titanium face of the Mizuno ST-230 driver

With the ST-Z 230 and ST-Z 230 drivers, Mizuno is still using the SAT 2041 forged beta titanium face. Quick reminder: SAT 2041 is low-modulus, high-tensile strength. Basically, it’s really strong and durable despite being more flexible than Ti 6-4 found in many designs.

For Mizuno, this driver release marks a new line in the sand. Starting with ST-230, Mizuno drivers will be on a two-year release cycle. This longer development cycle will allow Mizuno to make a bigger investment in fitting tools (fitting heads, shafts … that sort of thing).

That’s not to say the ST-230 X and ST-230 Z will be the only drivers in the ST-230 family. You can expect a line extension later in the year and most of you can probably guess what that will be. That one will also be on a two-year cycle.

Mizuno ST-230 Drivers Two Models

A photo of the Mizuno ST-X 230 and ST-Z 230 drivers

At this phase of ST-230 lifecycle, Mizuno will offer two models: ST-230X and ST-230Z. Their construction is strikingly similar. Both feature a 12-gram composite crown and a six-gram composite sole piece. The CORETECH Chamber assemblies are identical and both feature a 14-gram weight.

The differences between the two are found in the shape of the head and placement of that 14-gram weight.

Mizuno ST-Z 230 Driver


A mizuno ST-Z 230 driver head

If you’re familiar with recent Mizuno drivers, you already know the “Z” in ST-Z 230 is a reference to the clubhead’s Z-axis. The point of the name is to illustrate that, with the ST-Z 230 design, Mizuno is concentrating mass along the Z-axis (front to back).

Typically, this would be the part where we talk about shifting weight as far back as possible to boost MOI but Mizuno’s Chris Voshall wants to be clear: “The ST-Z 230 is not an MOI grab”.

Simply put: this isn’t a “maximum forgiveness” offering.

an address view of a Mizuno ST-230 driver

The ST-Z 230 is a balanced design in that Mizuno has concentrated some mass in the back (the 14-gram weight is centrally placed in the rear of ST-230 Z) but there’s also plenty of mass within the forwardly placed CORETECH Chamber as well.

If that sounds at all more radius-of-gyration theory, you’ve got it.


In reality, this particular “Z” is designed to position the center of gravity as close to the neutral axis as possible. In simple terms, we’re talking about closely aligning the center of gravity directly with true face center (which, FYI, it almost never is). That goes a really long way towards maximizing ball speed.

As far as the ball flight is concerned, the Mizuno ST-Z 230 is designed to be neutral (neither draw- nor fade-biased) and, while it probably won’t be Mizuno’s lowest-spinning model long term, a center of gravity close to the neutral axis suggests it should fall on the low-ish spin side while still offering reasonable MOI.

a profile view of a Mizuno ST-Z 230 driver

Mizuno says the ST-Z 230 driver has a classic pear shape and you can expect it to look square to slightly open (in standard setting) at address.

The Mizuno ST-Z 230 is available in 9.5 degrees (adjustable from 7.5-11.5) and 10.5 degrees (adjustable from 8.5-12.5). The 10.5 is available in right-hand only. Stock length is 45 inches.

Mizuno ST-X 230 Driver

a photo of the sole of the Mizuno ST-X 230 driver

If you learn only one thing about the Mizuno ST-X 230 driver, it should be that it’s not meant to be an anti-slice play. For sure, the “X” in the name is meant to imply that weight has been shifted along the X-axis towards the heel but Voshall says the X should be “the least draw-y” of any of the draw-biased crowd.

The objective behind the ST-X 230 driver isn’t to rival the PING G430 SFT. It’s simply about moving the center of gravity closer to the shaft axis and ultimately creating a club that’s a bit easier to turn over. Thinking of it as promoting a slight draw versus correcting a big slice.

To hammer that point home, there’s a near-even split in PGA TOUR use between the ST-Z and ST-X.

an address view of the Mizuno ST-X 230 driver

As far as the shape, the ST-X 230 sits a bit taller than the ST-Z and because weight has been pushed to the heel, the driver is a bit more rounded in shape.

Most will find it sits square in the standard setting.

The Mizuno ST-X 230 is available in 9.5, 10.5 and 12 degrees. Only the 10.5 will be available for lefties. Stock length is 45 inches.

Stock Shafts

A photo showing a UST helium and Diamana Kai'li shafts that are stock options in the Mizuno ST-230 driver

Stock shaft offerings for the Mizuno ST-Z 230 and ST-X 230 drivers include:

  • UST-Mamiya LINQ Red (High launch)
  • Mitsubishi Kai’Li Blue (Mid launch)
  • Project X HZRDUS RDX Smoke Green (Low launch)

A closeup of the Mizuno logo on the ST-230 driver

Mizuno ST-X PLTNM 230 Driver

Also available as part of the ST-230 line is the ST-X PLTNM 230, a lightweight alternative that effectively replaces the company’s J-Spec offering. The ST-X PLTNM 230 is 30 grams lighter than the standard ST-X 230. Notable in the PLTNM build are the UST Helium Platinum shaft and lightweight grip.

The Mizuno ST-X PLTNM is available in right-hand only in 10.5 and 12 degrees. The stock length is 45.5 inches.

A 44-inch women’s version is also available.

A closeup of the crown logo on the Mizuno ST-230 driver

Pricing and Availability

Retail price for the Mizuno ST-Z 230 and ST-X 230 drivers is $499.95. The ST-X PLTNM 230 is $549.95.

Retail availability begins Feb. 23. For more information, visit Mizunogolf.com.

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