What should we make of the new Mizuno ST-G driver?

Is it a line extension of the ST 230 driver lineup released this past February? Or is it a preview of Mizuno’s next driver lineup that, if Mizuno holds to its two-year driver lifecycle commitment, won’t hit the streets until 2025?

We do know it’s an on-time replacement for the two-year-old ST-G 220. But from there, the numerology gets a little fuzzy.

Mizuno’s ST 220 metalwood line came out in 2021. The ST 230 line followed in 2023 but without an ST-G. Today, we get a G, but with no numbers at all.

As Michael Keaton sorta-kinda once said: 220, 230 … whatever it takes.

Let’s dig into this Mizzy and see if we can’t figure out just where it fits.

Mizuno ST-G Driver

Mizuno has been on a one-year driver lifecycle since 2018 and the original ST180. The lineup has morphed a bit to include ST-Z, ST-X and ST-G models. In Mizuno-speak, the -X model tends to have a more rounded shape and be a tad draw-biased while the -Z model tends to have a more rearward CG and higher MOI.

The -G series has featured sliding sole weights and has been decidedly low-spinning.

So far, so good. But this is where it gets interesting.

When Mizuno was on its one-year product cycle, the ST-G model would come out this time of year while the -X and -Z models would come out the following January. By that cadence, an ST-G 230 should have come out last fall but it didn’t. The new ST-X 230 and ST-Z 230 drivers arrived on time this past January but Mizuno skipped a new -G altogether.

And now we have the ST-G with enough significant changes over the ST-230 line that it’s obviously a precursor to the next generation -X and -Z, which would have been due in January.

Only Mizuno has said it’s not going to do that.

In the big picture, unless you’re a release cadence cop, it really doesn’t matter.

What’s New?

 Compared to the ST-G 220, there’s plenty. And, compared to the ST 230 drivers, there’s enough new to whet your appetite for new ST-X and -Zs.

In keeping with tradition, the Mizuno ST-G features sliding sole weights that are the hallmark of the -G series. But breaking with tradition, the new ST-G is 440 cubic centimeters (previous ST-G models were 460). The new ST-G has a seriously deep face made from a completely new material for Mizuno: forged Beta Rich Ti-LFS.

Beta Rich Ti-LFS replaces the SAT 2041 beta titanium used in the ST 230 models. While the metallurgy is unclear, Mizuno does say the Beta Rich Ti-LFS face is seven-percent lighter and 15-percent stiffer than SAT 2041 while having nine-percent more tensile strength. This, friends, is all in the name of more ball speed.

The new Mizuno ST-G driver also features Mizuno’s CORTECH Chamber technology. It’s a small steel beam suspended in a TPU material on the sole right behind the face. The net effect is twofold. First, the steel/TPU mix allows the face to flex more, especially on low-face strikes. Second, at impact, the material in the CORTECH Chamber theoretically comes out of compression faster than the face. That delivers what can be described as an acceleration effect. Both of these are also done in the name of more ball speed.

Crowns and Weights

Any driver designer will tell you that weight savings is the Holy Grail. Any time you can save weight in one spot where it doesn’t do you any good allows you to reposition it someplace else where it will do some good. For the ST-G driver, Mizuno has developed what it’s calling a “wrap-around” composite crown. It extends over the toe’s edge and takes the place of the heavier material that makes up the rest of the body.

The new crown weighs 16 grams. For comparison, that’s about what a compact disc weighs.

And speaking of weight, the signature feature of Mizuno’s ST-G driver line is sliding sole weights. The previous ST-G 220 included two relatively short sliding weight tracks (one near the toe, one near the heel) plus a spot in the rear in case you wanted to put one or both weights there to boost launch and MOI.

The new ST-G is a complete sole redesign with two longer tracks that meet at the very back. This allows for endless configuration options to add or reduce spin and trajectory, add bias for fade or draw and boost MOI if needed. The sole weights weigh seven grams each which should make the ST-G a fitter’s delight.

The State of Mizuno Drivers

Mizuno’s decision to go with a two-year driver lifecycle makes sense. Meaningful improvements take time and if MyGolfSpy’s 2023 Most Wanted Driver testing tells us anything, Mizuno could use some meaningful improvement.

The ST-Z and ST-X 230 drivers were, to put it kindly, meh performers. Both finished in the lower half overall with the ST-X finishing near the bottom. Neither rated well with our testers on sound and feel. Mizuno feels they’ve addressed that in the ST-G with reinforced internal ribs to mute the sound.

With the new ST-G serving as the new baseline, we can probably expect the next ST-Z and ST-X drivers to feature the new forged Beta Rich Ti-LFS face design as well as the new wrap-around composite crown and internal rib structure. But if the cadence holds, we won’t see either until 2025.

The Mizuno ST-G, at 440 cc with a deep face, does offer promise for golfers looking for low spin and willing to sacrifice some forgiveness to get it.

Mizuno ST-G Driver: Specs, Price and Availability

The Mizuno ST-G will be available in 9.5- and 10.5-degree lofts for righties but only in 9.5-degrees for lefties. Each model is loft-adjustable up or down two degrees. The stock length is 45.25 inches.

Mizuno is offering two stock shafts for the ST-G. The mid-launch, mid-spin Mitsubishi Kai’ Li Blue 60 is available in regular and stiff. The low-launch, low-spin HZRDUS Smoke Green RDX 60 is available in stiff and X-stiff.

The Lamkin Crossline Genesis Full Cord is the stock grip. As always, Mizuno offers an impressive array of no-upcharge shaft and grip options.The new Mizuno ST-G driver retails for $599.95. It’ll hit retail Oct. 5.

For more information, visit the Mizuno website.

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