Sunday, June 27, 2021

adidas Adizero Prime X: Super Max!

Article by Derek Li 

adidas Adizero Prime X ($250)

Derek: The Adidas Adizero Prime X is Adidas’s no holds barred idea of the ultimate long distance training shoe. Notably, the marketing information specifically calls it out as being illegal for racing under World Athletics shoe regulations. They already have what they consider to be the best shoe they can produce within the confines of the current regulations and that is the Adios Pro (now into version 2) with its 39mm heel stack, and in the Prime X they have decided to supersize everything from midsole stack (up to a whopping 50mm heel stack) to a triple sandwich design of carbon rods AND carbon blades in the forefoot. 

There’s a lot going on, but is the Big Mac always going to taste better than the good old cheeseburger? Are things overdone? I’ve previously expressed my view that a higher stack is always going to be faster because you are working with a longer lever. Am I going to have to eat my words? Let’s dive in to find out. 


The cushioning you never knew you wanted - Derek

Very natural transition and a forefoot that doesn’t feel overly rigid - Derek

Very breathable upper - Derek

Good outsole traction - Derek


Very unstable heel at slow paces, maybe not the best for extreme heel strikers - Derek

Tongue is underdone, some friction points around eyelets as a result - Derek

Tester Profile

Derek is in his 30’s and trains 70-80 miles per week at 7 to 8 minute pace in mostly tropical conditions in Singapore. He has a 2:41 marathon PR.


Estimated Weight: men's 9.25 oz  / 263g (US9)  /  women's / (US8)

  Samples: men’s US9.5 9.56oz / 271g  /

Stack Height: 

Official 50mm heel / 40mm forefoot   (measured US9.5 at 52mm heel, 42mm forefoot)

Available now at $250  

First Impressions and Fit

Derek: My first thought when I held up the shoe in my local Adidas concept store was not so much “wow look at that stack”.  I think we’ve all grown accustomed to high stack over the past couple of years and visually, the heel doesn’t look all that impressive. There’s a reason for that. The Nike Alphafly with an official 40mm heel stack actually has a scalloped midsole design and if you measure the heel height externally, it actually comes to about 50mm. So externally, both Alphafly and Prime X will have heel stacks that look near identical. 

My first thought was actually centred on how thin and translucent the upper is. I’ve tested a lot of super thin uppers over the years from the Nike Zoom Fly SP to the VFNext% to any number of Skechers performance shoes that use incredibly thin uppers in the past 18 months (Speed Elite, Speed 6, Razor Elite, Razor Excess etc etc), but it’s the near transparent colour scheme that Adidas opted to go with that makes the Prime X upper look extra, extra thin. Then you also contrast that with a very thick midsole and the bottom heavy feel of the shoe is immediately apparent when you hold the shoes in your hands. 

Fit for me is true to size. The sizing was not so straightforward in this one. I usually wear a US9.5 and I tried both US9 and US9.5 back and forth a couple of times and ultimately decided to go true to size as I figured it would give me more leeway in terms of sock options. It turned out to be the right decision as I get just about 1 thumb space in front of the toes with Adidas Lightweight socks, and that’s what I prefer for all my shoes including race day. 

Walking around, the springiness of LightStrike Pro that you all love from the Adios Pro 1 is magnified several times over here, especially in the heel. The foam feels so unstructured that you really wouldn’t know there was a horizontal carbon plate in the heel if you didn't read about it in the spec sheet. 

The forefoot feels a little more like your regular Adios Pro in terms of stability, though the underfoot feel is still noticeably softer. You really don’t want to be walking on cobblestone roads in this shoe!  Next up is seeing how the shoe runs.  


Derek: Adidas calls the upper Celermesh 2.0 and you see some hints of the “old” Celermesh here in terms of the base material. It does not stretch much. Up front, a relatively soft internal laminate serves as a toe bumper to heel toe box height elevated. Unlike Celermesh 1.0, the internal webbing is greatly reduced and limited to larger strategic strips on the medial and lateral sides, and it focuses on locking down the foot at the level of the metatarsophalangeal joints. They even used something akin to Nike’s flywire technology for the front two rows of eyelets to reinforce the foothold. 

The heel counter is fairly soft and unstructured, and the collar is definitely less rigid than that found in the Adizero Pro or Adios Pro 1, so no breaking in required there. 

The tongue is a bit of a let down. You can appreciate that a lot of work went into stripping down the weight of the upper to its bare bones, but the tongue is one area I felt they should not have tried to skimp on material. At the minimum, there should be enough material to protect your feet from the more plasticky materials reinforcing the eyelets. As is, the tongue does none of that as it is very tapered at the front as you can see. 

When I run, I sometimes get a bit of irritation from the first eyelet directly above my big toe. In addition, the cutout in the tongue through which the laces slot seems to be a bit out of position for me, on both sides. The tongue seems to bunch up a little over there after a few miles of running. I’ve never actually experienced this with any other tongue before, not even on super minimalist shoes like the Reebok Run Fast Pro or Nike MayFly / Silverfish. I’m not exactly sure how to fix it except maybe they should have moved the slot slightly higher up.

Verdict: It’s OK. Not great. It’s not a very supportive upper, and compared to the Adizero Pro or Adios Pro, I view this as an inferior upper. I especially miss the elastic gusset band that Adidas used in the former two shoes. That band was incredibly good at supporting the midfoot. I think the flywire section works well at holding the foot at the met-heads, but arch lockdown is a little bit sloppy. Heel hold is non-existent and you get an almost free floating feeling at the heel but amazingly there is no heel slippage here so i guess it works well enough. For a training shoe, I think it’s passable, but I would prefer a more performance fit if I were going to try to do a hard tempo run in these shoes. 


Derek: This is where all the magic happens. The Adios Pro unveiled LightStrike Pro to the world and we loved it. The vibration dampening, the dense springiness, the durability, all of it. So what could go wrong when you take that and increase the thickness by 20%? Fortunately, not a lot. 

A lot of the key attributes of the Adios Pro are retained here. The curved anatomic carbon rods and the heel stabilizing carbon plates are still there.

And you have a little extra in the form of 3 more curved carbon blades to further enhance the forefoot rocker in a triple layer LightStrike Pro forefoot foam layup. Above is a screenshot of the breakdown and position of the rods and blades in the midsole  from the adidas website. In red are the rods, and in orange are the carbon blades. You can see that they are fairly narrow and I believe serve more to preserve the stiffness of the forefoot rocker against the backdrop of a thicker 40mm midsole. I suppose they could have gone with thicker rods of some form but they likely decided it was lighter and maybe less expensive  to do a new mold for 3 thin blades than a new mold for 5 carbon rods. 

The high heel stack conveys a soft (maybe overly soft) marshmallowy feel at the rear, and while there is a plate in there to aid with stability, there are zero medial or lateral stabilizing elements. You will need good mechanics for this one, and maybe a stable road surface too. Anything too cambered and you might roll your ankle if you land very supinated. The beveled heel, which is a hallmark of so many Adidas shoes is also present here. It may give you the impression of being even more unstable as a landing platform. I wouldn’t be able to tell you because I just don’t land that far back. I tried to test it. 20% downhill incline. Nada. Had a lot of fun trying to brake at the end though.

The midsole actually transitions fairly naturally and you don’t feel the rods or blades underfoot at all, unlikely in the Adios Pro. The high stack allows you to compress the forefoot enough to get a bit of virtual flex through the toe joints before catapulting your foot forward. 

The rocker is there, but it’s not really in your face like a Zoom Fly 1, but rather is more subtle and natural like a NB FuelCell TC or Puma Deviate Nitro. Really quite nice. The vibration dampening ability of the midsole setup is incredibly good, right up there with the Nike Alphafly and NB RC Elite 2. The foam does have a tendency to collapse medially at midfoot, I think partially because there are a lot of cutouts on the medial arch, so this shoe is going to be a hard pass for people who need some form of medial midfoot stability in the shoe. That said, forefoot stability is decent, with the rods and blades doing a good job of giving the soft platform some underfoot stability. 


Derek: The outsole is very similar to the Boston 10. There is excellent durability and grip. I think the outsole and its grip is especially important here because it helps to enhance the stability of the shoe. The soft and thick midsole also allows Adidas to get away using some relatively firmer rubber compounds without adversely affecting the underfoot feel of the shoe. The chevron striped design affords excellent grip on both roads and gravel, though I don't recommend using the shoe off-road due to stability concerns. 


Derek: The ride is surprisingly natural. For all the tech that is poured into the shoe, it transitions nicely and smoothly, without any particularly strong forefoot rocker sensation or anything else that really feels like it is helping you transition through the shoe faster. Instead, the focus seems to be more on vibration dampening and cushioning, and the carbon elements serve more to improve stability and give the forefoot some snappiness. You will feel the rods and blades working here in the way you feel the carbon plate rocking you forward in the Nike Alphafly: you don’t. You just don’t. 

This is a superb cruiser that should have no problems handling some marathon pace efforts, though it’s forte would likely be those moderate effort long runs. It is going to feel good in the sense that you don't get sore at the end of long efforts, but in terms of mechanical assistance, it is, perhaps, surprisingly, not all that special for me. It is also great for slower efforts, but be warned that the longer you stay on that heel, the more wobbly you are likely to find it. 

There is a bit of a bottom heavy feel to the shoe, and it becomes a little more pronounced the faster you go, but the overall weight of the shoe is still fairly light for the amount of stack we have here. It’s about the same weight as a Nike Pegasus or Nike Tempo Next% after all, so in terms of absolute weight, it’s still right in that wheelhouse. 

Conclusions and Recommendations

Derek: If you are looking for a super shoe that will give you that 10% improvement, you are going to be disappointed. This is not that kind of shoe. Not sure that shoe will ever exist, and I am not sure I want it to exist to be honest. Part of the enjoyment in running comes from knowing your fitness is borne of sweat and tears, and throwing up by the track right?? 

The Prime X is an uber trainer with best in class cushioning, but that is the best attribute of the Prime X for me, as it is not some special super shoe that makes you even faster than the Adios Pro. It will be a great training companion to the Adios Pro for those progressive long runs or long runs that need a little marathon pace work. The cushioning is special enough that I think people who can afford it, should at least give it a try. This shoe can be quite unstable so unless you are comfortable in very unstable neutral shoes as the NB Fuelcell TC, Nike Alphafly or ASICS Novablast, this shoe is not for you. 

Derek’s Score 9.30 / 10

Ride 9.5 (50%) Fit 9 (30%) Value 9 (15%) Style 10 (5%)

Watch RoadTrailRun Editor Sam's Review of the Prime X

11 Comparisons

Adidas Adios Pro 1 (RTR Review) (RTR Review Adios Pro 2)

Derek: I wear US9.5 in both shoes. As stated in the review. The Prime X is really more of a trainer equivalent to the Adios Pro and not a racer per se. If you like the Adios Pro as a racer then definitely consider the Prime X as a more durable, more cushioned trainer version. I would get the same size for both models, though the fit of the Prime X is a bit more relaxed. 

Adidas Boston 10 (RTR Review)

Derek: I wear US9.5 in both shoes. The Prime X is significantly bouncier and softer and noticeably less stable compared to the Boston. Both have similar fits and outsole characteristics so it mostly comes down to how much stability you like in your trainers. The rocker mechanism is actually more prominent in the Boston than the Prime X for me. 

ASICS Metaspeed Sky (RTR Review)

Derek: I wear US9.5 in both shoes. This may come as a strange comparison, but the Sky has a similar kind of forefoot softness to the Prime X, with the Prime X having a slightly denser sort of bounce. In both shoes, you don’t feel the carbon element or stiffness when you run but more the foam characteristics so they are similar in that respect. I think fans of the Sky can also consider the Prime X as a trainer equivalent, though take note that the Prime X has a traditional 10mm drop with the Sky 5mm. 

ASICS GlideRide (RTR Review)

Derek: I wear US9.5 in both shoes. GlideRide has a softer underfoot feel than Prime X and both shoes have a similar degree of ground feel (or lack thereof). Prime X has a more springy forward guiding ride to it and you will find it easier to up the pace in the Prime X. Overall, I prefer the ride of the Prime X. Huge price difference though. 

Nike Alphafly (RTR Review)

Derek: I wear US9.5 in Prime X and US9.0 in Alphafly. One of the few shoes that can challenge the Prime X for price, and stack. The Prime X will be an easier shoe to run in for heel strikers. The weight difference is significant, and I think for racing purposes and speed work, the Alphafly would still be the better option. Prime X would be better for easy runs and daily training. In terms of stability, Alphafly’s heel is softer and more unstable, but the forefoot seems more stable with the airpods than Prime X. 

Nike Tempo Next% (RTR Review)

Derek: I wear US9.5 in both shoes. Battle of the super trainers here. As cushioned as the Tempo Next% is, the Prime X has noticeably better vibration dampening. Prime X also has much better outsole grip, especially on wet surfaces. The fit of the Prime X is significantly more relaxed so people who find the Tempo too snug will definitely want to try the Prime X. That said, the Tempo has a much more stable heel, and a noticeably better “assisted” transition. The difference is quite stark once you try to go up a mild incline in both shoes. In terms of overall versatility and the ability to perform uptempo work, I think the Tempo Next% is still a better shoe. It doesn’t hurt that the Tempo is less expensive too by a considerable $70. 

Nike ZoomX Invincible Run (RTR Review)

Derek: I wear US9.5 in both shoes. Both shoes are about the same length, but Invincible has a snugger fit feel in the heel and midfoot. Invincible is much softer and mushier underfoot, but has about the same amount of heel stability as the Prime X for me as the softness is sort of cancelled out by the lower stack in the invincible and its broader platform at the rear. Prime X doesn’t sink in as much and feels like a sprightlier ride all round, at all paces. Add in the superior outsole and I definitely prefer the Prime X as the more versatile and fun shoe to use. 

New Balance RC Elite 2 (RTR Review)

Derek: I wear US9.5 in both shoes. RC2 has a snugger heel and midfoot, but the toebox is similar volume to Prime X. Here again, I think Prime X would make for an excellent trainer complement to the RC2. RC2 is softer and smoother through transition, as the Prime X has a denser bounce to it. The overall balance of RC2 is better with Prime X having a more bottom heavy sort of feel. Prime X has the better outsole in terms of grip for me. If you can only have one shoe, definitely get the considerably lighter RC Elite 2. 

New Balance Fuelcell TC (RTR Review)

Derek: I wear US9.5 in both shoes. Hard to believe it now when we were salivating over the cushioning of the TC just a year ago, but the Prime X has much less ground feel and better cushioning than the TC. Even harder to believe that the 2 shoes are almost the same weight! The TC is one of the few shoes with a more unstable heel than the Prime X, but this is once again cancelled out by the lower stack of the TC. Overall, I think the TC is a more versatile shoe that feels easier to do some speed work in. Both shoes use very unstructured uppers so fit and lockdown are quite similar. At $200 for the TC and $250 for the Prime X, I think the Prime X is a more unique ride, but lacks the versatility of the TC. If you have multiple shoe options, I’d get the Prime X. If you have limited options or just one shoe, then TC is the better choice. 

Puma Deviate Nitro (RTR Review)

Derek: I wear US9.5 in both shoes. While both shoes look like they have similar uppers, the fit is surprisingly different. Prime X has a more relaxed and wider fit, yet seems to be easier to dial in than Deviate Nitro. Prime X is significantly softer and more cushioned, but less snappy when you want to pick up the pace. With the Deviate Nitro costing much less, I think it is the more versatile overall option, but the ride is much more special and enjoyable in the Prime X, especially for longer and easy runs. 

Skechers Performance Max Road 5 (RTR Review soon)

Derek: I wear US9.5 in both shoes. Prime X has the more relaxed fit all round. Both shoes have a similar denser sort of bounce to the foam, but Prime X has noticeably less ground feel due to the higher stack. Prime X is also more unstable in the heel than MaxRoad due to the higher stack. That said, the forefoot of the Prime X seems to be more predictable as it has more continuous outsole rubber coverage  compared to the podded outsole (and midsole below) of the MaxRoad 5. MaxRoad 5 is less forgiving at moderate and easy paces for me, and neither shoe is my preferred choice for uptempo work. Overall, Prime X is the better shoe. Bear in mind though we are talking $250 vs $135 here. You can almost get 2 pairs of MaxRoad for a pair of Prime X. 

The tested sample was a personal purchase. RoadTrail Run has affiliate partnerships and may earn commission on products purchased through affiliate links. These partnerships do not influence our editorial content/ The opinions herein are entirely the authors'.

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