Mizuno Wave Sky 9 review

After testing the Mizuno Wave Sky 9 in our lab, we believe it is:

• Perfect for neutral runners who are after a premium daily trainer with top-end materials and a plush ride.
• Suitable for long-run enthusiasts who need endless cushioning that lasts throughout the run.
• A good upgrade for those who enjoyed the Wave Sky 8 but felt it lacked traction or breathability.

We can identify three issues with the Wave Sky 9. The energy return is surprisingly low and has decreased from its predecessor. For a similar shoe with better energy return, check out the Asics Novablast 5.

Its stability is still lacklustre, despite its wider base, making it ideal only for neutral runners. Moreover, its price might deter runners from buying it. If you want an option similar to the Wave Sky 9 but without breaking the bank, consider the Nike Vomero 18.

Like its predecessor, the Wave Sky 9's midsole appears extremely cushioned, and our lab results confirm it. With a staggering 145 SA in the forefoot, the impact protection of this Mizuno shoe is on par with the Nike Vomero Premium! Not to mention that its heel remains above the average at 142 SA, delivering a cloud-like ride that will definitely please runners looking for maximum shock absorption.

It's always sad when the successor doesn't surpass the previous version, and this is exactly the case with the energy return in the Wave Sky 9. With an uninspiring result of 45.2% in the heel and 47.1% in the forefoot, it has almost 10% less energy return compared to the Wave Sky 8. 

With a stack height of 44.3 mm, the Wave Sky 9 surpasses its predecessor in the maximalist shoe range, making the ride even more cushioned.

If you are wary of towering platforms, you can choose the New Balance Fresh Foam X 1080 v14 for a lower stack with the same quality of cushioning.

The stack grew taller not only on the heel of the Wave Sky 9. Mizuno also increased its forefoot stack height by nearly 7 mm compared to the previous version. Those last miles of a long run will definitely become more comfortable with this shoe!

The 6.2 mm drop measured in our lab confirms the brand's 6 mm claim. However, we were surprised to see a 4mm reduction in the shoe drop from the Wave Sky 8 to the 9. 

The new offset limits the shoe's versatility, appealing primarily to midfoot and forefoot strikers. 

Although Mizuno ditched the bubble-like midsole design for the Wave Sky 9, the new wave-like construction feels just as squishy, with a durometer reading of 14.5 HA.

That’s because Mizuno retained the same innovative nitrogen-infused Enerzy NXT foam for the top layer of the new version’s midsole.

Meanwhile, the bottom layer is made of standard Enerzy. In the previous Wave Sky 8, the compound was much firmer (26.4 HA), which helped stabilise the ride. But in the new Wave Sky, it softened up to only 19.3 HA, making it less effective as a stabilising factor.

The gel mould we got from filling the Wave Sky 9’s interiors with custom liquid confirmed that this shoe is true to its medium width.

With a 95.7 mm width between the big toe and the pinkie, we can see that Mizuno kept the fit standard, accommodating runners with medium-width feet. However, the brand also provides wide-size versions in certain markets like the USA or Japan to accommodate runners with broader feet.

At this point, we realised that Mizuno had adopted a more snug, toebox fit for the Wave Sky 9 compared to the previous version. 

Measuring the mould in the big toe area, our calliper showed only 70.4 mm, which is almost 5 mm smaller than the Wave Sky 8. If you are looking to buy this shoe, be wary that the toe box may not be as spacious as you think, or opt for the wide version for extra space.

The toebox of the Wave Sky 9 is also below average in height, measuring just 22.8 mm with our calliper.

The good thing is that the upper material is flexible enough to allow some toe wiggling.

Recording an impressively high friction coefficient of 0.64 in the Wave Sky 9, we were elated to see a major outsole traction improvement over the previous version. We felt way more confident on slicker pavements in this Mizuno shoe!

The shoe is generously covered with the X10 carbon rubber, keeping the grip consistent from heel to toes. But the cutouts and exposed foam areas in the outsole keep the weight down and make the ride more fluid.

The higher stack height of this shoe also resulted in greater bending stiffness, compared to the previous edition. Our 30-degree bending test, confirmed that the Wave Sky 9 requires as much as 25.1N to bend the forefoot, which is 72%(!) more force than it took the Wave Sky 8!. 

However, the added stiffness provides greater support during the toe-off phase, helping us push off the ground more effectively.

More foam means more weight! And we couldn’t help but notice the extra ounce the Wave Sky 9 gained over the Wave Sky 8.

At 10.4 oz (295g), the Wave Sky 9 is slightly above the average weight for a daily trainer, but we don't consider it excessive for a maximalist (40 mm+) shoe!

The shoe's weight gain is definitely not due to the knit upper, which is thinner in this version and has better ventilation!

The smoke-pumping test yielded a score of 4/5, which is adequate for premium road-running shoes.

We can tell that Mizuno kept the structured upper around the midfoot and heel and invested in a more perforated knit for the toebox.

Examining the shoe under the microscope, we see the tiny gaps that were already slightly visible to the naked eye, and we confirm that this is a high-quality upper.

The lack of breathability in the previous version was addressed in this version, while keeping the quality and padding of the Smooth Stretch Woven upper. At last, the upper matches the shoe’s price point!

The Wave Sky 9 is a 100% neutral running shoe and, from our perspective, doesn't suit runners who are looking for stability features. The added softness of this version doesn’t make the situation any better for runners with flat feet and overpronation.

But on the bright side, we noticed that Mizuno made some vital adjustments to increase the Wave Sky 9’s inherent stability and balance out its higher stack and softer foam with a stiffer build and wider platform.

The Wave Sky 9 earned the highest 5/5 score in our torsional rigidity evaluation, largely due to its higher stack!

In our thorough evaluation, the Wave Sky 9's heel counter is notably rigid, earning a 5/5 for stiffness. Most of that stiffness comes from the abundantly cushioned heel, enveloped in plush padding and ensuring a snug fit. 

To compensate for the plushier ride, Mizuno had to widen the base of the Wave Sky 9. Our precise caliper measurements confirmed that the forefoot dimensions widened from 114,7 mm in the previous version to 120 mm in this one. 

The same was applied to the heel dimensions, where the area width increased from 93.5 mm to 99.9 mm. This rise in width might appeal to runners who tried the Wave Sky 8 but wanted a wider shoe base!

The Dremel test on the Wave Sky 9 showed us everything we wanted to see in this shoe: an impressively durable knit that was only slightly scratched! 4/5 on this one.

We are always happy at RunRepeat when brands address our concerns. Mizuno improved heel padding durability from the Wave Sky 7 to the Wave Sky 8, and we did not expect another improvement in the new version. But we earned one! 5 out of 5 for the Wave Sky 9 means a durable heel counter that will last you for miles and miles.

Improved outsole traction and durability? Yes, the Wave Sky 9 has it all. We noted a 1.1 mm dent in the outsole after our Dremel test, which is right on the average for daily trainers and an improvement from the Wave Sky 8.

Nailing the composition and distribution of rubber in the outsole enabled Mizuno to reduce layer thickness by 3 mm. This might save a few grammes, but could it mean that reduces the lifespan of the outsole?

The insole thickness, at 5.2 mm, is noticeably thicker than average, enhancing the shoe's plush feel.

The removable insole of the Wave Sky 9 is pretty vanilla, with no standout features. If you want to add support to the shoe, you can substitute the insole with a custom orthotic!

We almost lost the Wave Sky 9s in our lab when we turned off the lights. The absence of reflective elements in this version sounds like a downgrade to us!

We found a 7.8 mm-thick triple-layer foam in the shoe's tongue, similar to the Wave Sky 8. The slight thickness reduction from the previous version will not compromise the comfort and lockdown feel this model provides!

We were very surprised to see a slight change in the lacing system. For this version of the Wave Sky, the punched-eyelet system was abandoned in favour of a slashed hole, which, given Japanese engineering, is as reliable as the latter!

Something we always expect from a high-end daily trainer is a gusset. The Wave Sky 9 has a partial gusset made of a stretchy material, combining a snug feel with a lightweight design.

The Wave Sky 9 is the flagship in Mizuno's daily running shoe lineup, especially given its higher price point compared to models such as the Wave Rider 29. For this price, you get a superior midsole, a grippy outsole, and high-quality upper materials. On the other hand, we believe that when compared to other daily trainers from other brands, this shoe is slightly overpriced.

The Wave Sky 9 includes a longer heel collar that provides Achilles support and makes it easier to slide your foot into the shoe.