adidas Adizero Prime X 2 Strung  ($300)

Introduction

Sam: The Adizero Prime X 2 Strung, adi’s beyond max cushion 50mm heel trainer racer, sees an all midsole geometry with a broader platform at the rear and midfoot (and no longer with a giant notch), a lower drop (more front cushion) along with an all new dual carbon infused non Energy Rods plating system. Lightstrike Pro supercritical foam continues but is now in two densities as we have a softer core between the plates up front. The Strung upper is tuned with more heel and midfoot fibers and a new stretch knit tongue. 

We do see a substantial gain in weight as a result of the new more substantial geometry. Is it still fast and race worthy if “illegal”  for elite marathoners due to its giant 50mm heel and 43.5mm forefoot? Does it still have that unique wild and hard to control sensation of flight? Well, Patrick Lange ran a triathlon marathon segment world record of 2:30:32 (2022) in the Prime X 2 Strung in a prototype where the height limits of World Athletics do not apply.  Let's find out whatJoost (a multiple World Marathon Majors winner in his AG including a 2:26 at Berlin in 2019, Sally 2x on the podium at NYC in her AG, and RTR Editor Sam who moves along at slower paces discovered.

Pros:

Massive & deliberate riding platform with bottomless responsive cushion: Sam/Joost/Sally

Practical: considerably more stable than the original due to wider heel midfoot platform, new more extensive plating, and more secure upper: Sam/Sally/Joost

Secure and supportive upper: new stretch knit tongue and slightly thicker zonal Strung material: Sam/Sally/Joost

Now Adizero’s long distance fast trainer and beyond max racer and less of a novelty: Sam

More heel striking and downhills friendly than v1: Sam

Excellent traction with extensive Continental rubber outsole layer: Sally/Joost

Paces still faster and easier than perceived effort: Sally/Joost

Still a dramatic fast ride with nice bounce, but not the wild sensation of flight of the previous version: Sally

Doesn’t feel as heavy as it is: Joost/Sally

Cons:

Heavier, stiffer, more stable and less front dynamic: missing some of the sensation of flight of v1 with its less extensive more dynamic Energy Rods springier feel: Sam/Sally

Substantial 2.15 oz / 61g  gain in weight  to is felt but does not overwhelm:  Sam/Joost

More versatile and practical but still “concept car” pricing: Sam/Sally/Joost

Still not a slow paces or heel strike friendly shoe. Requires 9 min miles or faster to really work: Sam

Harder to pull on the foot with the knitted tongue, and harder to dial in the lace tightness with the thin string-like cotton laces (and resultant lace bite): Sally/Sam/Joost (agree on the tongue, don’t see any issue with laces and lace bite)

Stats

Approx. Weight: men's  10.85 oz / 307g ( US9) 

Actual Weight:    women's  9.1 oz / 258 g (US 6.5/W8)

  Samples (unisex sizing): men’s  10.6 oz / 300g  (US8.5) 

                                                      9.1 oz / 258 g (US 6.5)

307g - 315g / 10.83 oz - 11.11 oz (US 9.5)

Stack Height: 50 mm heel / mm 43.5 forefoot ( 6.5mm drop spec) 

Platform Widths (italics PXS1) 

heel 80mm / 75mm, midfoot 70mm 50mm, forefoot 110mm / 110mm

Prime X  1 Strung  49.5 mm heel / 41 mm forefoot, 8.5mm drop , 8.68 oz  /  246g US9

$300. Available now including at our partner Running Warehouse HERE

First Impressions, Fit and Upper

Sam: The X 2 upper features adidas Strung technology. With Strung the actual fibers are not only differentially placed for varying density but are of different characteristics based on purpose and are oriented in different directions. The upper is coded and laid down thread by thread based on the data.  Adidas describes Strung as follows: “STRUNG,  (is) an industry-first textile and creation process that allows us to input athlete data into the precision placement of each thread in any direction we choose. We can build and test different structures in the software before sending our chosen design to the STRUNG robot, which places each thread into a single composite with specific performance zones and properties”. 

The X 2 now has additional layering of fibers in the midfoot and heel and gets a stretch knit tongue in place of the thin and quite frankly ineffective  un gusseted tongue of the prior version. 

Over the top midfoot volume is reduced by the stretch and the top fit is now snug and secure. 

I do notice a touch of lace bite from the narrow laces and thin stretch knit tongue in lacing to my narrower feet but no real issues.

The lacing moves from 5 eyelets to 4 which is sufficient for me given the stretch knit tongue.  Further, instead of having lace loops right along the throat of the shoe, they move further down to draw the lower part of the midfoot upper around the foot more completely.

The heel has additional Strung blue fiber layering and while it does not have a heel counter and is still pliable it is now more than adequately held. I did a runner’s knot lace lock that made the hold yet better. No issues with heel or mid foot hold whereas in Strung 1 a half size up I used near hiking weight socks and still had a very shaky rear and midfoot hold. 

The X 2 now has a true performance fit worthy of the Adizero race performance heritage.

The toe box and entire upper, given the Strung construction, is not particularly soft and pliable and for sure is non-stretch. They are quite hard to pull on, a good thing in my book as any stretch here would affect the hold on such a giant platform underfoot. 

 I tested with moderately thick SmartWool run socks and had adequate toe box room and especially good overhead volume yet with solid hold. The only fit/comfort issue was some moderate lace bite especially when using a runner’s knot. I think low volume narrow feet might at least try a half size down from their normal.

The fit is true to size for me, unlike Strung 1, which at a half size up in my sample and which was way too big all around. 

Sally: I was fortunate to test the first version of the Prime X Strung for RTR last year, and to this day consider it the most amazing shoe I have ever had the privilege of running in. My conclusion in the Prime X 1 Strung review posted last year included the following:

So OF COURSE I was excited to try the update; who doesn’t like the effortless sensation of flight while running? 

Right off the bat I could tell that Adidas had made some changes. Yes, the massive 50 mm stack height is still there, and the intriguing upper with computer woven threads (similar to a Kevlar sail) is still there.   

The upper has changed from a thin gusseted tongue to a stretch knit tongue, hopefully allowing a more custom fit. The geometry of the midsole has changed, more on that later. As for the fit, my pair of V1 were size unisex 7.0, which felt at least one half size (or even one full size!)  too big for my narrow W8.0 feet. Even with my heaviest socks, the oversize of that pair most likely contributed to the wild unstable (but fun) feel. 

My pair of V2 arrived in unisex size 6.5, which fits much more true to size. This upper will easily accommodate a high volume foot, as it is a bit roomy for my narrow foot. 

But otherwise it is a nice snug customizable fit made possible by the knitted stretch tongue. I do wish the laces and/or the lace loops had some anti-slip mechanism - I found it a bit difficult to dial in the tightness without the thin laces slipping back after pulling tight. 

Not to be sexist, but I also wish Adidas would make a women’s specific size so we narrow footed women runners did not need to wear the typically roomier unisex version.

Joost: This is actually my first pair of Adidas Prime X. Lots of my athletes run in the original and a few in the Strung version. I borrowed a pair of the original Prime X to be able to compare both and ran some miles in them before receiving my pair of Prime X 2 Strung. The Prime X v1 (sans Strung) feels very energetic and wild as Sally puts it, but too unstable on the badly laid brick road with 90 degree turns I tested it on. Let’s see then what’s different in this all new “illegal” shoe. Paraphrasing Adidas promo material: since it’s illegal, they didn’t feel confined in any way to experiment and put technology into this flagship maximum cushioned dual plated shoe.

The Strung upper is a piece of art in itself. Close-up, there are different types of fibers criss-crossed in visually random directions, creating an upper that has some flexibility in key areas like the lateral area where the pinky toe sometimes needs that little extra space and more stiffness in other areas. 

As far as I can see, there are 3 main layers of fibers, in different colors. The base layer is blue, followed by a layer of red and finally a layer of white fibers on top. 

In the heel, there are  diagonal stretches of extra blue fibers for some support, since there is no internal heel counter. The end result is a little less breathable than you would expect, but still perfectly ok here in the tropics.

The first three eyelets are loops that are firmly stitched into the Strung upper. The last two are on a patch of synthetic material. The stretch tongue is stitched into the upper. 

It’s not an easy shoe to get into, but the heel tab helps get your foot into the shoe without problems. 

There’s a little cushioned padding in the heel collar that helps keep the heel in place. My feet felt like they were held well on the platform at all times, even on turns. 

The laces are very thin, but they didn’t cause me any bite, in spite of the fact that I have to tighten them a fair bit to hold my Stryd pod in place.

Fit is roomy true to size for me with enough room for my wide feet. If you’re in between sizes and your feet aren’t too wide, you might want to pick the lower size and save a bit of weight in the process. 

Midsole

Sam: The stack height moves to 50mm heel (+0.5mm) and 43.5mm forefoot (+2.5mm) with a completely new geometry. Most notably, the midfoot moves from a platform width of 50mm (cutouts) to 70mm while the heel gains 5 mm in width to 80mm with the front of the shoe unchanged at 110mm. The changes to the midsole geometry ( and new plate system) leads to a substantial 61g gain in weight in a US9 to 10.85 oz / 307g.

The foam(s) remain Lightstrike Pro in 3 layers of 2 firmnesses/densities. All foams and especially the top layer are very very slightly softer than in the original’s to pressing. Lightstrike Pro is a very responsive quick reacting supercritical foam that sits for me between firmer ASICS Blast Turbo Foam and Saucony PWRRUN Hg as in the Elite and softer foams such as NB FuelCell and Saucony PWRRUN Pb. It is a touch firmer and less springy in feel than Nike ZoomX.

The top 2 layers are the same firmness to pressing while the white  front “core” between the 2 plates shown above is clearly softer.  

The 2 plates overlap for most of the length of the shoe. with the softer core insert between them up front while at the heel the lower plate rests on a foam insert of some kind as does the longer top plate at the rear. 

The plates are well masked by all the foam but remain propulsive in a more deliberate flatter and more consistent way than the original Prime X, think big fast BMW vs Ferrari. 

There is a final toe spring curve upward of both plates and especially the more aggressive lower one (as shown in the schematic above)  providing the necessary push off roll through the lower foam for this entirely rigid shoe. This spring is far more noticed as present walking than on the run but for sure it is there and effective given the giant stack.

 Compared to earlier Prime X with their Energy Rods, the front rebound is less springy and the feel more cushioned and rigid favoring more a stronger vertical push than the prior’s roll and spring.

The heel has a prominent lateral crash pad whereas the v1 had none. 

Interestingly I think this lateral crash pad helps make walking in them super fun and slow paces (10:30 mile or slower for me) very awkward and stilted. The shoe then comes back into its “prime” as pace gets down in the mid 9 min miles or faster.

Joost: Sam has described the technical stuff in great detail. While looking at the description, you would be inclined to think that the increased height in the forefoot could possibly make the Prime X 2 more unstable in the forefoot than the original version, but the fact that it now has a wedged dual plate instead of a plate and energy rods makes for a forefoot that’s a little stiffer and actually feels more stable.

As Sam noted above, the foam wedged in between the two plates is notably softer than the top and bottom layers. The other big difference with the original version in the forefoot is a rocker that’s a lot more aggressive. The lateral side of the forefoot is also more rounded off than the medial side, further adding to the feel of the rocker. The rocker reminded me a bit of the New Balance SC Trainer v1, but there’s a lot more foam overall in the forefoot here.

The heel looks quite exotic when seen from behind. It’s decoupled, with the lateral side (right above) also more rounded and sloped than the medial side, offering added stability and some control for heel strikers. Being wider also helps in this department. Even as a non-heel striker, you eventually touch the ground with your heels and that extra width helps create a more stable ride.

There are a couple of cutouts that show off the internal plates. In the center of the midsole, you can actually see both plates, because there’s a similar cutout in the bottom plate that lets you see the top one.

Sally: There is a lot of midsole to discuss here, specifically 50 mm worth created by three layers of LIGHTSTRIKE PRO framed by two carbon-infused plates, and Sam and Joost have analyzed it in great detail. I will simply add that despite its massive stack height, V2 is more stable and controlled and a bit less springy than V2. With a higher and wider forefoot/midfoot, the drop has been reduced but the fun forward rocker is still there. There is less wild but exciting sensation of flight when pushing the pace here, but still smile-inducing bounce.

 I agree with Sam that it is a comfortable walking shoe, but not so comfortable to “jog” at mellow paces in. The more you put into it, the better they feel. I am rebuilding my training base and speed as I rehab a nasty high hamstring injury (can I build fitness and endurance fast enough now to run Chicago in 5 ½ weeks?)  so I don’t think I have been able to enjoy what this shoe can do at speed… yet. I look forward to future miles when I get back to racing form.

As a bonus, we height challenged folk (I am 5’2”) always appreciate a literal lift underfoot (but you won’t find me in high heels) and this shoe makes me feel TALL. 

Outsole

The outsole is Continental rubber and there is lots of coverage with only the central channel not covered. There is plenty of grip while the coverage provides a consistent landing and push off surface. 

The red medial coverage is in two layers with the outer piece adding thickness for a touch of stability as it is slightly firmer. The Adios Pro 3 has a similar film at its medial heel. It is a different compound than the rest of the outsole as when running a finger over it is smoother and less tacky than the black rubber.

While I have not run on wet roads yet, I did on fine beach sand over pavement and the grip is remarkably good, better than many other shoes and most race shoes. There is a very slight slip then grip kicks in and decisively at each stride as I think there is so much consistent gripping surface across the whole bottom front of the shoe.

Looking at the underside, both outsole and geometry, we can clearly see the differences between the v2 and the original.

Gone is the very narrow 50mm midfoot platform with its giant cut out as well as the narrow 70mm heel area which, with a stack height of 50mm, was for sure not a place to linger at or to pound downhills in. Things are now broader and more squared off (80mm at the heel and 70mm at the midfoot  and more stable all around at the rear of the shoe. I think adidas went a bit too far though (not open enough at midfoot and the 2.5mm higher front stack)  as some late pronation at the front of the midfoot to start directing towards the toe is lacking if one is more of a rolling stride vs. a vertical midfoot forefoot lander. 

Joost: Good old Continental rubber. Adidas has a proven track record using it and while this version is a bit reminiscent of the Adios Pro 1’s “Formula 1” outsole, there’s more than enough traction. Going off the Adios Pro 1, durability also won’t be an issue.

Sally: There is plenty of Continental rubber surface underfoot here, as Sam illustrates. I put it to the test on a very rainy run and the good traction on wet roads was appreciated. No stones gather in the cutouts, and the outsole gets medium grades for quietness. The wider platform, particularly at the heel, makes a noticeably more stable base. 

Ride, Conclusions and Recommendations

Sam: The Prime X 2 Strung is a radical max, max cushion shoe that is now a far more practical trainer racer than its wild predecessors where one had to be focused and aligned at all times.. or else to experience its wonderful and unique sensation of flight. 

With dual broad and full carbon infused plates and even with 2.5mm more stack height upfront, the forefoot it is a bastion of now stable and front rebounding energy t

That is somewhat tamer but still special. It does lose some of the forward rolling drive due to its considerably higher weight, lower drop/higher forefoot stack and with less of the springier flight sensation that the Energy Rods provided in the last versions. We have a more deliberate and controlled experience and as I said before is more akin to a heavy and very fast BMW than the previous near race car Ferrari where a soft touch and focus control was key.  In many ways the changes are a good thing.  

I wonder why adidas did not retain the prior front construction with Energy Rods which was so special in its sensation of flight and just implemented the new broader, more stable rear platform and the new more supportive upper. Further, reducing the stack height somewhat and keeping the higher drop would have increased the drive to the front of the shoe and reduced the weight increase from a more substantial rear of the shoe.  

Don’t get me wrong, the new Prime X 2 Strung is a far more practical shoe than its predecessors. adidas is to be congratulated in pushing boundaries of what is possible and making such a giant shoe more usable for more runners than just those who could handle its wild ancestors.  

While it does not quite deliver the “sensations” of the prior versions,  it is still an Adizero high performance shoe for sure and a far more solid and practical max max cushion fast trainer and racer, making it a better value than before.

Sam’s Score: 9.31 /10 😊😊😊1/2

Ride (50%): 9.3 Highly protective/cushioned and deliberate in its energy but now on the heavier side for racing and with prior sensation of joyous flight toned down.

Fit (30%): 9.4 Much improved upper matches big stack height in performance, not easy to do

Value (15%): 8.9 Decent but wish X was more pace versatile

Style (5%): 9.4 Cheery adding some color to the massive slab underfoot

Joost: I have been struggling with a nasty bout of retrocalcaneal bursitis and due to the fact that I run a bit differently to protect me from the pain it causes on the run, I seem to have strained a ligament on the lateral side of my foot between my heel and my ankle. This in turn makes it quite painful to turn left (it’s my right ankle) while running and any wrong step hurts as well. (it does “warm up” after a couple of miles, though). I mention this because I was afraid a shoe with a 50mm heel on relatively soft foam would not be ideal.

Where the Prime X 1 (sans Strung) was too unstable and hurt quite a bit, the Prime X 2 (avec Strung) seems quite a bit more stable to me. It’s probably a combination of the extra width in the heel, the superb upper, the plate in the forefoot instead of the energy rods and the rocker that creates the extra stability I needed. The rocker also helps a lot with my heel, since the perception of the shoe’s drop is actually very different from the measured drop.

As a mid to forefoot striker, the combination of the plates, the humongous amount of bottomless feeling foam, the secure upper and the rocker create a very fast feeling ride. As Sam mentioned, more of a front forward pushing, guided ride than the previous version. I prefer it this way. At over 300g for a US 9.5, it’s a rather heavy shoe, but they definitely don’t ride as heavy as their official numbers would suggest.

The Prime X 2 Strung is destined to take the place of favorite shoe in my rotation from the New Balance SC Trainer v1. This is partly because the NB have 1000 miles on them and the plate in my right shoe seems to have developed a small crack in those last few runs, but also because the Prime X is a joy to run in. It is very fast, in spite of its bulk and for a non-professional athlete, it can double as a trainer/racer, almost justifying the $300 price tag.

Joost’s Score: 9.71/10

Ride (9.9 - 50%): Fit (10 - 30%): Value (8.5 - 15%): Style (9.7 - 5%):  

Sally: Adidas has tamed the beast. (Or at least put training wheels on it.) In some ways I am sad and I will miss the wild uncontrolled feeling of flight of the initial Prime X Strung, but the changes make for a much more practical and versatile super max cushion trainer. The original required elite focus and fitness to perform as intended. 

This is still a very high performance innovative massive stack fast trainer that might also double as a race day shoe, but it is more stable and tame and thus more suitable to a wider range of runners. The combination of multiple carbon plates and a tremendous stack of Lightstrike Pro foam make for a fast, rocker propelled forward ride with plenty of bounce. 

Fun to run in, It will definitely be tops in my rotation as a gentle on the legs faster tempo long run shoe. As technology keeps improving and evolving and all prices of running footwear are creeping up, the $300 price tag does not seem out of line for such an innovative performance shoe.

Sally’s score:  9.43 /10

Ride: 9.6 (50%)   Fit: 9.5  (30%)   Value: 8.7  (15%)  Style:  9.5 (5%)

😊😊😊😊

6 Comparisons

Index to all RTR reviews: HERE Roadtrailrun 

Prime X Strung 2022 (RTR Review)

Compared extensively in the review. X 2 is more stable, heavier, and more practical for more runners.

Nike Alphafly 2 (RTR Review)

Joost (M9.5 in both): I actually laced up my Alphafly v2 a while ago for a long interval tempo session. They felt just like I remembered them: in need of a lot of power pushing down and adjusting the gait to that in order to get the energy back. The Prime X, in spite of the extra 10 mm of foam in the heel, has an easier ride. As a training day shoe, there’s really no contest. The Adidas is a lot more enjoyable for me. For a marathon, I would have to take the Prime X for a couple of really long runs in order to decide if the extra weight is not a factor and if very tired feet create instability. My hunch is it stays more enjoyable than the Alphafly 2.