Adidas Adizero Prime X 2 Strung review

We've concluded that the Adidas Adizero Prime X 2 Strung is an outstanding choice for:

• Those who enjoyed the fun and bouncy ride of the original Prime X but felt it too unstable—we've found this update delivers enhanced support.
• Marathoners unconcerned with World Athletics regulations who prioritise ultimate cushioning and technology regardless of cost and rules.
• Anyone with at least £300 in the bank to invest in top-tier engineering—we're convinced the technology behind the upper, midsole, and outsole make this shoe a real masterpiece.

The Prime X 2 Strung by Adidas really showcases what they are capable of, but it's a double-edged sword because of its high weight. It's clear for us that this shoe isn't the best choice for short races, and we're hesitant to recommend it even for half or full marathons. Instead, we suggest the Nike Vaporfly 3 or the Adidas Adizero Adios Pro 3.

For a thrilling and unique running experience, we believe models like the Hoka Cielo X1 and Mizuno Wave Rebellion Pro 2 offer a similar ride with much less bulk.

Moreover, the steep price tag of the Prime X 2 Strung may deter many runners. We think there are better choices out there for those seeking a max-cushioned running shoe—options like the Hoka Mach X or the ASICS Superblast stand out in our analysis as top supertrainers.

Adidas advertises the Prime X 2 Strung with a staggering 50 mm of stack height. While we observed that it might reach this impressive height in the midfoot area, our official measurements following World Athletics guidelines show it to be 45.7 mm.

This is the tallest shoe we've ever measured in our lab to date. Of course, it's technically illegal for racing, but you'll be fine if you're not an elite competitor, age grouper or going for prizes in World Athletics-regulated races.

This results in nearly infinite cushioning in the heel, transforming the shoe into a dream for those seeking peak performance coupled with best-in-class muscle protection.

This feature is especially advantageous for heavier runners or those competing in gruelling races with fatigued legs, such as an Ironman. Conversely, runners with lighter frames might find it overly bulky and, definitely, bottom-heavy.

Enormous, gigantic, colossal, vast and monumental. These words capture the towering stack height of the forefoot, as evidenced by our measurement of 36.9 mm.

Simply put, the Adidas Adizero Prime X 2 Strung offers more cushioning in the forefoot than many shoes have in their heel, making its level of comfort truly mind-blowing.

While Adidas advertises this shoe as having a 6.5 mm drop, our precise measurements revealed an offset of 8.8 mm. This difference it's negligible, yet it slightly favours heel strikers, making the PX2S more suitable for their running technique.

The midsole of the Prime X 2 Strung is among the most incredible we have ever analysed in our lab, and we're eager to detail each component for you.

We began with the largest slab of Lightstrike Pro, located closest to the ground. Surprisingly, we found this superfoam to be quite dense, registering at 24.3 HA on our durometer.

Why is it firmer than other superfoams? For us, the primary reason appears to be stability. Given the shoe's significant stack height, a firmer midsole at the base helps to control unwanted lateral forces.

The secondary foam in the Prime X 2 Strung extends from the heel to the forefoot and is positioned closer to the foot. This layer, softer than the first at 14.9 HA, is designed to offer plushness and comfort, and it rests directly above the carbon plate.

Lightstrike Pro is among the most resilient foams on the market and performs consistently across a wide temperature range. Therefore, we weren't surprised to observe only a minor 12.9% difference between the room temperature measurements and those taken after chilling the shoe in the freezer for 20 minutes.

We found that the Alphafly 3's insole is impressively thin, measuring only 2.8 mm. However, it's made from EVA, which provides limited energy return compared to the midsole. For the Prime X 3, we have a suggestion for Adidas—consider creating an insole made from Lightstrike Pro!

This is a first for our lab—we typically test running shoes featuring single-density foam, and occasionally, models with dual-foam setups like the Nike Vomero 17. However, the Adidas Adizero Prime X 2 Strung features not one, not two, not three, but four distinct foams in the midsole.

This smaller piece of Lightstrike Pro is sandwiched between two carbon plates and is the softest of all, registering at just 11.0 HA. This setup allows for exceptional compression and impressive energy return, creating an industry-first design.

We've now reached the fourth and final foam in the Prime X 2 Strung lineup, and arguably the most intriguing of them all, because it's not Lightstrike Pro! It's called Energy Core and it's really plush at 11.5 HA. 

So, what exactly is Energy Core? It's Adidas's latest foam innovation, and we suspect—Adidas does not talk about it—that it may be the same material used in their £490 Adios Pro Evo 1, crafted from supercritical Pebax instead of TPEE like Lightstrike Pro. 

Its placement and small size raise questions here in the lab. We think it's designed enhance softness in the heel (like ASICS does with PureGEL in the Nimbus 26), suggesting that Adidas might be also testing this foam for a more prominent role in the upcoming Prime X 3.

As hinted earlier, the Adidas Adizero Prime X 2 Strung has replaced the Energy Rods with two carbon plates. The top plate extends from the forefoot to the heel with a flatter shape, enhancing stability and energy storage, while the bottom plate sports a spoon shape that cradles the ultra-soft Lightstrike Pro, creating an effective sandwich design that promotes turnover.

It might help to envision it as a blend of the Alphafly's flatter plate and the Vaporfly's spoon-shaped plate—combined into a single shoe. It's clear that Adidas idea is to just go all out with the Prime X.

Undoubtedly, this dual-plate setup delivers a uniquely bouncy ride that also enhances stability, but it significantly increases the shoe's weight. This added heft can compromise performance at faster paces, so whether this trade-off is worthwhile depends on how you prioritise weight in top-tier running shoes.

It's also worth noting that this shoe is technically ineligible for races due to its dual-plate setup due to its updated rules: "The one rigid plate or blade referred to in Rule 5.13.1 may be in more than one part but those parts must be located sequentially, in one plane, not in parallel (i.e., not stacked above each other), and must not overlap."

Given its thick midsole and inherent stiffness, the only logical design choice was to incorporate a substantial rocker to smooth transitions and enhance forward motion, especially beneficial for those lacking robust toe mobility and strength.

There’s a pronounced forefoot rocker that initiates quite late, paired with a flared and bevelled heel—features that are common in most Adidas supershoes. Thus, it's clear that this shoe gets as far as possible from the traditional racing flat design.

Although capable of handling marathon racing—particularly for those targeting over three hours due to its weight—we believe the Prime X 2 Strung truly shines in long run quality workouts. This is exactly why we were eager to try and measure its toebox.

The vertical space for the toes has been reduced compared to the previous Prime X, which excelled in this area. The toebox is now significantly flatter.

We discovered a fit that straddles the line between a racer and a training shoe, measuring 96.0 mm at the upper's widest part. In essence, those with regular feet will find it suitable for long runs and races, but should not expect the spacious interior typical of a daily trainer.

After measuring the big toe area (76.1 mm), we identified why the shoe felt in a middle ground to us. 

It may appear broad in our photos, but that's due to the narrow heel, which creates the illusion of a wider toebox.

When we first examined the shoe in the lab, our initial thought was—there's no way this shoe can offer stability with such a towering stack height. Yet, it does.

A smart combination of design elements contributes to this unexpected stability. The widened midfoot, robust midsole sidewalls, the Strung upper and the dual-plate configuration all work together to deliver a surprisingly stable ride. Remarkably, we can even recommend it for runners with mild stability needs!

With its innovative design featuring two carbon-fibre plates encased within a massive midsole, we anticipated a max score in our manual torsional rigidity test.

True to our expectations, this turned out to be among the most rigid shoes we've ever attempted to "twist". Indeed, we used quotes because it's impossible to twist the PX2S—earning a 5 out of 5 from us.

On the other hand, the heel counter of this shoe is remarkably flexible, scoring a mere 1 out of 5 for rigidity. This softness and the lack of padding in the area led to some heel slippage during our tests—however, we managed to mitigate this issue effectively by employing a runner's knot.

A notable improvement in the latest Prime X is the expanded midsole width, particularly noticeable in the forefoot, now measuring 115.2 mm. While it's not exceptionally wide compared to other competition shoes, this increase is definitely noticeable while running.

The heel remains narrow at just 81.6 mm, underscoring the Prime X 2 Strung's racing intent despite its substantial weight. This narrow design may not favour heel strikers, but the broader midfoot and stability from the dual plates adequately compensate for this.

In this lab review, we've emphasised that the PX2S features a dual carbon plate design within its midsole, contributing to extraordinary longitudinal rigidity.

From our 90-degree bend test, the Adizero produced a formidable stiffness, clocking in a massive 76.6N in our force gauge. Although such stiffness might typically suggest incompatibility with easy paces, the ultra-thick cushioning of this shoe does allow for occasional easy runs, contrary to what one might expect.

We conducted another 20-minute freezer test on the Prime X 2 Strung to assess its performance in extreme cold temperatures. Afterward, it required only 8.8% more force to flex the shoe, resulting in a total of 75.1N. This is exactly what we anticipate from a superfoam.

Here's the major drawback of the Prime X 2 Strung—it's notably heavy at 10.8 oz or 305g, and frankly, despite Adidas' best marketing efforts, there's no way to sugarcoat it. It weighs nearly 2 ounces more than its predecessor!

Despite the weight, performance isn't entirely compromised, as the significant energy return from its incredible midsole does offset most of the energy loss. Yet, it really feels bottom-heavy while running. From our perspective, it's like driving an Audi A8 instead of a Ferrari—perfect for highways, but less suited for racetracks.

Adidas's Strung technology is a novel approach to upper design, focusing on data-driven thread placement to maximise ventilation and structural support across the shoe. This allows for precise customization of the upper, enhancing airflow and stability where it’s most needed.

During our evaluation, the Prime X 2 Strung particularly impressed us in the toebox area. Our tests revealed outstanding ventilation, earning a solid 4/5 rating. When we illuminated the shoe, it became evident how the upper's thickness transitions from the heel to the forefoot, showcasing the variable design.

Using a microscope, we got an up-close look at how Strung technology meticulously fuses threads in all directions into a singular, seamless piece of mesh.

This detailed view highlights the technical precision and the advanced nature of this fabrication method, which optimises both function and form. Look at that ventilation hole!

Despite its lean build focused on performance, the Strung upper also proved in the lab to be surprisingly comfortable. 

Of course, we found it lacks the heavy padding found in more traditional running shoes, particularly in the heel area, yet it still manages to deliver a satisfactory level of comfort.

After getting a good outcome with the breathability test, we were ready to test the durability of the pricey £300 Prime X 2 Strung with our Dremel—especially painful since we purchase every shoe we test to ensure that we produce unbiased reviews for you.

Revving the Dremel to 5K and applying a consistent 3.2N of pressure, as we do with all our shoes, the Strung upper proved remarkably kevlar-tough, and scored a perfect 5/5!

Riding high from the success in the first two tests, we then assessed the heel collar of the shoe, hoping for at least a satisfactory result. To our delight, the PX2S wowed us once again, clinching another perfect 5/5.

We can now affirm that the Strung technology has emerged as one of the most remarkable innovations we've encountered here in the lab. However, its complex manufacturing process and high cost are downsides that limit its application across a wider range of shoes.

This shoe showcases the pinnacle of Adidas technology—it's like a window into their absolute best capabilities. And naturally, it features Continental rubber.

However, our analysis revealed a diverse mix of materials: Continental rubber at the front, a sandpaper-like Stealth rubber covering most of the outsole, and Crystal rubber from the heel to the midfoot.

As the majority of the outsole utilises the Stealth, we measured its hardness at 60.4 HC, raising concerns about durability. However, as expected with such soft rubber, the grip it offers is truly exceptional, one of the best we've ever tried in the lab.

Despite our initial reservations, the Prime X 2 Strung stunned us with a gold-medal-worthy performance in our durability test.

After the Dremel tried to wear down the rubber, we meticulously measured the depth of the abrasion repeatedly to confirm the accuracy. Indeed, the damage was minimal—only 0.3 mm, marking one of the best performances we've ever recorded in the lab... for a shoe with such grippy, super-soft rubber!

We also measured the outsole thickness, which registered at just 1.5 mm. Given the impressive durability demonstrated previously, we think Adidas can trim it down a bit more, even though it's significantly thinner than most other shoes.

We're big fans of Strung—it's truly awesome. However, it isn't reflective yet. Imagine how awesome it would be if Adidas developed a full-reflective Strung upper?

We're big fans of Strung—it's truly awesome. However, it isn't reflective yet. Imagine how awesome it would be if Adidas developed a full-reflective Strung upper?

The tongue of the shoe is exactly what you'd expect from a competition model—remarkably thin, almost like paper. We measured it at just 1.0 mm using our callipers, so don't anticipate plush comfort in this area, and be sure to tie your laces with care before any run.

Oh, and we must also point out how appalling it is that Adidas continues to use the same cheap laces found on an average budget running shoe in a £300 model. Come on, give us notched laces!

The original Prime X and Prime X Strung had a conventional, non-gusseted tongue, so it was quite surprising here in the lab when Adidas overhauled the whole area with a bootie-style design.

Whether this new design is better or worse really depends on personal preference. If you favour a traditional tongue, you might not be a fan of the new knit version. However, if you're looking to avoid tongue slippage and desire a secure fit, this bootie-style design could be exactly what you need!

Continuing the trend set by recent Adizero models, the PX2 features a flap-style pull-tab on the heel. This addition not only improves the shoe's look but also makes slipping your foot into the Strung upper much easier.

You can replace the insole of the Prime X 2 Strung with another one, but be aware that the shoe's narrow heel and limited interior space might not comfortably fit third-party or custom orthotics.

Additionally, retaining the stock insole has its perks—it features a perforated design that enhances heat dissipation. This is a cool detail, and frankly, for 300 bucks, it’s something we expect!