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Hoka One One Carbon X2 Multiple Tester Review
By Chief Founder Matt Klein and Contributor David Salas

The original Hoka Carbon X (REVIEW) was among the initial recent release of carbon fiber plated footwear to the market. Developed for the Project Carbon X in 2019, this was a great ultramarathon racing shoe. The amount of cushion present allowed it to double for many as a lightweight trainer and a workout shoe. The design of the plate and outsole created a high level of natural stability (without a post) that allowed me to use from everything from easy runs, workouts, uptempo long runs and everything in between. Although too heavy for me personally to use as a race shoe, it worked very well for a large population of people wanting a bit more cushion with a plate for long distance races, but not something so aggressive or unstable as the Nike Vaporfly series. With the Project Carbon X 2 coming, the second version evolves with Hoka's current development of footwear. Featuring a longer midsole, lighter weight and new geometry, the Carbon X 2 continues as an excellent trainer/racer combo. Whether it will break more ultra distance records remains to be seen.

The Hoka Carbon X2 in hand. A red upper with Hoka written over the midfoot. A slight flair in the heel. White profly midsole throughout.

Specifications for the Hoka One One Carbon X2 (per Running Warehouse)
Weight: 8.5 oz (Men's 9)
Stack Height: 39mm/34mm
Drop: 5mm
Classification: Ultra Marathon Racer


Matt: The Hoka One One Carbon X 2 is an ultra distance racing shoe that will work for many people as a marathon racer, others for its intended purpose and many will find it as a great lightweight trainer. Updates include the midsole geometry, slightly softer ride, a narrower fit, an extended posterior dovetail heel flare and what feels like a slightly narrower sole. The CarbonX series gets more aggressive in this update but still works best during longer uptempo efforts.

The HOKA ONE ONE Carbon X2 is a Marathon to Ultra Marathon racing flat designed to break the 100k world record in the coming weeks. I think HOKA delivers. The updates from the original model include re-engineering of the carbon fiber plate, softening of the midsole, and extending a beveled heel flare with aims of creating smooth transitions from heel to toe. The shoe is incredibly smooth at controlled rhythmic efforts and I think they hit the money on this one.


Matt: The fit of the Hoka Carbon X 2 fits true to size in my normal men's size 10 although I thought it fit a hair short initially due to the snug fit throughout. A breathable, thinner mesh upper covers the forefoot and midfoot, which extends into a heel with thicker overlays. As mentioned the fit overall is snug but very secure. I have not had to lace lock the shoe at all and the mesh is comfortable enough that I didn't get any blisters on a long uptempo 20 mile run. The heel is locked in fairly well. There is a heel counter, but the additional padding around the collar and the elf heel protected my heel bone quite well. I did get a little heel slippage the first few miles, but that quickly went away. The tongue is secure and thin. The notch sits very comfortably against the ankle and it is secured on each side with two small straps. Most of the reinforcements in the upper are in the heel. The midfoot and forefoot are mostly unstructured. The laces lock the midfoot down quite well and sit against the foot well. The forefoot is definitely snug and was quite noticeable at first. There is more of a racing fit throughout, so those with narrow to medium width feet will do better in this shoe. The mesh in the forefoot does stretch out after a mile or two, but is noticeable each time I put it on. Even with the very long runs I have used it for, this snugness has never been a problem as the miles picked up, so know the upper also takes a bit to "warm up." I don't normally comment on this, but the insole is glued down in the Carbon X 2. Walking and while breaking the shoe initially, it feels like the midsole is slipping, but I think that has more to do with the way it is glued down. Every time I check it is still quite secure, so just know it might feel like that. I am the only one of our group that experienced this, so maybe it is just me. I have to note that unlike the original, I would not go sockless in this shoe. The upper is comfortable with socks but the mesh is not as soft as the previous version.

The fit of the HOKA ONE ONE Carbon X2 is pretty dialed in throughout. I'll begin with the upper and the materials. The upper is incredibly comfortable with a breathable yet reinforced mesh that holds up well in turns has a nice snug fit on the foot. The heel has a nice hold on it being normal width to perhaps slightly narrow, but does a good job of preventing any heel slippage in such a high stack shoe. The midfoot is normal width to slightly narrow as well, but very dialed in and did not cause any excessive irritation. The toe box is definitely a tad narrow for such a long distance shoe. I did not have any problems with irritation on my foot, but I do think this might be too narrow for some folks out there in the toe box. The tongue and lacing do a good job of locking the foot in without beign overly tight or padded for a racing shoe. It is just protective enough in that region. There is a semi-rigid heel counter present but it is contoured well and padded just enough to allow for some security and lock down without being overbearing. This honestly is one of my favorite uppers I've run in, with the toe box being the only thing I feel might not work for some people. The upper might also be a tad thick for a racing shoe... but this is also a 100k racing shoe and I would prefer comfort with breathability rather than pure lightness so this isn't a big deal for me.


Matt: The Hoka Carbon X 2 took me a bit to figure out. This shoe is best for consistent uptempo paces but has a little flexibility to extend itself both into slower and faster ranges. The midsole is thicker than the original and features a new posterior dove tailed heel flare. the forefoot still has a great flare that provides a really nice stable ride up front. The front is my favorite part of this shoe. The toe off is fantastic no matter what pace you are going. The plate has a new design that I discuss more in the Stability section, but is integrated very well with the toe spring. I have used this shoe for both a 20 mile steady state as well as 400s and not had an issue. This shoe is a little heavy to be used for racing anything under a marathon for me, but can move if you want it to. As mentioned, it feels best at uptempo paces, which for me has been in the mid to low 6 minute per mile range recently. Trying to move the shoe into tempo paces (5:40-5:50) made me notice the weight much more. However, trying to sprint in the shoe actually feels good, which I suspect is partially from the plate and the smooth mid/forefoot design. On the other end of the spectrum, easy runs fell decent, while recovery runs can be a little too stiff. The heel I will talk about in a second, but its stiffness makes slower recovery runs a bit unpleasant if you land farther back. To me, this shoe is really best as an ultramarathon road shoe that will also work well for many people as a half marathon and marathon racer if they are looking for more cushion. The forefoot transition is smooth and stable, with a rocker that matches the stiffness very well. The midfoot is similar in that it has a smooth, stable ride. The transition is secure and seamless. For those that land a little farther forward at the midfoot or forefoot, this shoe will shine. The heel was less smooth for me. The extended flare was noticeable and despite the pronounced heel bevel, I still felt like I was hitting the ground early. This was particularly evident while I was warming up as the shoe felt very stiff and cumbersome. When I would warm up and pick up the pace, the Carbon X began to shine. I have used this shoe for several easy runs and that feel has slowly improved as the shoe has loosened up. However, the heel feels a bit stiff for those who land extremely far back. I have started to wear at the outsole (also perhaps because of that early heel contact), but there is plenty of material there that even though I have worn a significant patch of the outsole smooth, I still have a long way to go. One of the limitations of the original is that I shredded the midsole and was only able to get 160 miles out of my pair before I had to retire them. This was due to the fact that I very quickly wore a significant amount of the lateral heel away, creating an artificial wedge that quickly irritated my ankles and knees. There is still so much material to go that with the thicker midsole and outsole I expect to get significantly more miles out of these, likely in the lightweight trainer range (200-300) or far above).

The HOKA ONE ONE Carbon X2 has an incredibly fluid ride, but at designated paces. This is a shoe that I can do a little bit of everything in, but I definitely wouldn't reach for it for anything below the marathon distance. It is designed to be a marathon to ultra marathon shoe and I feel they did a great job with that specific distance range. The midsole is soft and protective with a significant rocker feel to it throughout. The carbon fiber plate adds some rigidity to it throughout and also adds some pop at toe off. The foam isn't Zoom X soft, but feels almost like an in between density to the Endorphin Pro and the Rocket X in terms of durometer. It is very protective, soft for a general racing shoe, but still a little firm compared to a lot of the high stack marathon racing shoes out there. The extended heel flare in the midsole has the aim of creating a meta rocker and to ease the transition from initial contact at heel through the midfoot and ankle rocker stages in the gait cycle. For some the heel flare might generate an early contact and not be a good thing but I had no problems with it in this shoe. The Clifton Edge was overkill for me and I did notice it, but in the Carbon X2 it seemed to serve its purpose pretty well. The outsole is also a soft rubberized EVA. Don't worry there is PLENTY to burn through and I don't think durability is really a concern here. The outsole reminds me a little of a tire, the softness of it almost gives it a stickiness when on the road and does surprisingly well with traction. This is definitely lost when taken off road, but the shoe does ok in those conditions for being a road shoe. Speed wise this shoe does really great at rhythmic controlled efforts for me. It peaks out right around marathon pace, goal pace for me being 5:15 to 5:20. I have taken this shoe at sub 5 paces and it felt ok, but just a lot of shoe to push at a pace like that. For me though the sweet spot is in the rhythm. Everything from 5:35 to 6:45 pace effort wise for me was really smooth. I can do easier warm up/cool down efforts in this well pretty comfortably, but this really dialed in in that controlled steady pacing. It is almost the perfect long run shoe for me and can be pulled out for longer tempo runs as well. So... at marathon I'm still leaning Rocket X for weight and responsiveness, but you could make a case for Carbon X2. I think a very large majority of people are really going to enjoy this shoe for the marathon distance though in the recreational population because of the protection and how well it does in rhythm.  


Matt: Despite not having any posting, the Carbon X 2 has one of the most stable forefoot designs out there. The plate has also been redesigned to split and curl under the lateral digits. It still has a design that facilitates appropriate use of the 1st MTP joint, but has an added bonus of facilitating the foot to resupinate in the later stages of gait. This is very natural (or it should be) and feels really good, particularly when the pace picks up. It is also quite stable thanks to both medial and lateral sole flare, raised sidewalls and a centered bevel. The raised side walls are noticeable from a stability standpoint, but are integrated very well into the midsole. This is a very stable shoe and like the original, I have no issues taking this shoe for long distances on road. For those that need mild to moderate stability, this shoe will do well as a racing shoe if you want a bit more cushion underfoot. For those that don't need stability, there are no aggressive methods that will push your foot one way or the other.

For such a high stack racing shoe the HOKA ONE ONE Carbon X2 is incredibly stable. The ride is developed well with the heel bevel and toe spring and also has some guidance measures built in. The carbon fiber plate has a slit in it allowing for flexibility through the great toe to keep motion moving naturally forward. The upper is also reinforced really well and can take turns or hard motions as well. The foot feels secure and moves really well in rhythm with the shoe. At top racing speeds the shoe can be a bit unstable just because it does lose a little pop and the high stack and weight make it a bit awkward, but in rhythmic controlled efforts the shoe is very stable. Again, this is a marathon and beyond shoe. It isn't necessarily designed for efforts faster than those, though it can dabble if it really needs to. 


Chief contributor David Salas looks at the HOKA ONE ONE Carbon X2 after 100 miles and gives his feedback on the durability of the upper, midsole, and the outsole.


David: HOKA ONE ONE did something really interesting with the design of the Carbon X2. They created a carbon fiber plate that attempted to mimic the natural motion of the foot. In the gait cycle the foot moves through a series of transition points called rockers. The rocker points are at the heel, ankle/midfoot, and ultimately through toe off (key word toe) where the foot transitions off of the great toe (your big toe). What HOKA ONE ONE did to try to mimic this motion was to focus on the path of least resistance. They created a carbon fiber plate where the plate extended through the second digit, but was nonexistent through the first great toe, but present roughly up until the metatarsal. What that did was give that region of the shoe a little bit more flexibility and a path to follow throughout the gait cycle. In theory, you should have 60 degrees of great toe extension to accomplish running and movement in a linear trajectory. So because the shoe is less rigid in this point, the foot will be more inclined to travel in that direction, while also allowing for some flexibility in the great toe. For me personally, I think they do accomplish this task for I do feel a little bit more flex in the shoe at that region when springing off of the forefoot. With how much foam there is on the shoe it does feel a little more subtle though. I applaud them for approaching this shoe from a biomechanical perspective though.

Matt: I really loved the plate design of the original Carbon X. The continuation of this in version 2 is great!  The design features a split forefoot design, with the lateral component extending into the toes while the medial component stops early. This is supposed to facilitate pivoting off the first metatarsophalangeal (MTP) joint (toe), which is what you are supposed to do to properly engage the windlass mechanism of your foot. This involves appropriately using the plantarfascia to transfer forces and stabilize the foot to allow for a fast and stable toe off. This is great for those who need a little guidance or want a fast toe off. For those however with hallux rigidus or any joint mobility issues of the first toe, this might be a problem. Usually shoes with a stiff and rockered sole will take pressure off this area as the toe spring and stiff sole reduce the need for use of the natural forefoot rocker, ie extension of the toe joints. For normal mobility, you should have about 60 degrees of extension at the first MTP joint (preferably 80 for runners). For those that don't have this, toe spring is a great way to reduce the need for motion at this joint. Carbon fiber plates can increase load at the MTP joint by moving joint reaction forces farther forward and this design may put a little more load through this area. For those with normal mobility here, this design may help with efficiency, stability and the transition at the forefoot. However, for those with pathology of the first toe, approach this design cautiously. Dear Hoka, that does not mean change this design. I love it and it will work for a large population very well. This is just a word of caution to a unique population. 


Matt: I still don't fully understand the extended posterior heel flares Hoka has been using recently. The rearfoot of the original Carbon X was way smoother. So if Hoka can find a way to smooth that out or even use a heel bevel that extends farther forward, that will make this shoe smoother at the rearfoot. Like David, my other recommendation is to not only widen the forefoot, but soften the inner mesh. I loved using the original sockless (did up to 16 miles without blisters) and would love to see that design return.

The main recommendation I would make for the Carbon X2 would be to widen the toe box slightly. Since it is an ultra marathon shoe, one would have to expect a certain degree of swelling. The toe box has just enough room for normal toe splay, but especially for those with wider feet they may have some trouble in this category, especially in latter miles. As an ultra shoe and long run shoe I really like this shoe. More of a comment than recommendation, I would like to see HOKA to make a shoe right in the middle of the Rocket X and the Carbon X2 that can really dial in on a fast marathon with protection and responsiveness.


David: The HOKA ONE ONE Carbon X2 and the Rocket X are very different shoes from each other. One is a racing flat that can tackle everything from 5k to marathon (Rocket X) and one is an ultramarathon racing shoe that could also do well at marathon for some (Carbon X2). The Rocket X is less protective than the Carbon X2 overall with significantly less stack height, but increased responsiveness through the forefoot and lower in weight. The Carbon X2 has a more pronounced rocker to it and relies heavily on your rhythm at a controlled tempo. I've taken the Rocket X at 4:45 mile pace with no problems, but do acknowledge that marathon is about the farthest I'm willing to take it. My goal marathon pace at this moment would be 5:15-5:20 per mile and the Rocket X is very smooth at that range and I would say "just enough" protection to get you to the finish of the marathon. The Carbon X2 is designed for beyond the 26.2 distance. For me the shoe is smooth as butter at 5:45 pace and above, including easy paces but really starts to struggle below 5:30 pace for me. However, it is an excellent long run shoe option, and I think a shoe that will work for a larger population of people at the marathon distance than the Rocket X since most people won't need that extra bit of responsiveness and lower profile in the Rocket X.  If I generalize the statement: Rocket X everyone 5k to half marathon, elite marathon and some sub elite marathon. Carbon X2: Recreational to sub elite marathon, elite ultra marathon, awesome long run shoe for all as well. 


Matt: The Hoka Carbon X 2 is a lightweight, carbon fiber plated, maximalist ultra distance racing shoe. This shoe should work well for those looking to run hard for road ultramarathons or those who want a little more cushion and protection for half marathon and marathon race distances. The Carbon X 2 is more aggressive than the original version, making it lean a bit more towards the racing end of the spectrum, but the amount of cushion still makes it a viable option for those who want to train in a carbon plated lightweight trainer. The shoe does best at uptempo paces, but can handel a little deviation up and down pace wise. The snug upper is secure and should work for those with medium to narrow feet. The Carbon X 2 has a very stable design, so while it has not posting, there is enough natural stability that those with neutral, mild or moderate stability shoes will be able to use this shoe for longer distances runs and races. For those looking to run long distances fast who land a little farther forward, I recommend this shoe if you want a carbon plated ultramarathon specific shoe. Just be aware that the Carbon X 2 takes a little bit of time to break in, so be a little patient.

The HOKA ONE ONE Carbon X2 is a high stack ultra marathon racing shoe for those that like to burn rubber on the road. The shoe also does great with long runs and should work really well as a recreational marathon racer for many people. The shoe is surprisingly stable on the road for the high stack height and does incredibly well in controlled uptempo rhythmic paces. It loses a little pop at faster paces, but isn't necessarily designed for that. I think this a shoe that will for a lot of people due to its smooth geometry and ability to protect the legs for long miles.


Fit: A-  (Comfortable even if forefoot fits a bit narrow initially)                     
Performance: B+ (Super smooth forefoot/midfoot, but clunky heel with posterior flare. Great for uptempo paces and certainly a marathon/ultramarathon racing shoe for many) 
Stability: A (Very stable for a neutral race shoe. Especially stable forefoot design) 
DPT/Footwear Science: B+ (Really great stability design, particularly at the forefoot. Unique use of plate, however I am still confused for the reasoning for the use of the posterior heel flare.) 
Personal:  B+ (This shoe continues to grow on me. Great ride overall that has worked for me as a cushioned lightweight trainer and great for steady state workouts) 
Overall: B+ (Really great shoe that continues to grow on me. It continues to improve as it breaks in and the forefoot/midfoot are incredibly smooth. That heel just needs a little work though and that A grade will happen)              

Fit: A- (Very dialed in and a very imrpessive upper overall. Narrow toe box for an ultra shoe however, not great for wide accommodation)                    
Performance:  A-
 (VERY smooth at controlled and uptempo efforts like ultra, but very difficult to push at performance paces including elite marathon type pacing, wouldn't do speed sessions in this shoes but long tempo's ok) 
A- (For the high stack it is very stable from heel to toe, but does get a little sloppy at faster paces, but... its an ultra shoe) 
DPT/Footwear Science:  
(HOKA did a great job with innovation and trying to match the shoe to natural biomechanics) 
(I really like this shoe. I put 36 miles on it within 3 days, over 50 in a week with other shoes testing at the same time. I wouldn't race in it, but this is an amazing long run shoe and tempo shoe for longer efforts) 
Overall:  A- (An awesome shoe for its purpose, very niched, does lose some versatility at higher end speeds but overall I am very pleased with Carbon X2)              

Thanks for reading!


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We broke the X2 even further down this week with a special podcast episode on Doctors of Running Virtual Roundtable! Listen in here:

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Dr. Matthew Klein is a 140 lb male with notable PRs of 14:45 for 5k and 2:32:44 for the full marathon.  He typically runs 70-100 miles per week and trains at a variety of paces from 8min per mile recovery runs to 4:40 per mile 1k repeats.  He prefers firmer and responsive shoes with snug heels and medium to wide toe boxes.  He is particular to less cushioned shoes and close to the ground shoes, but can handle a little cushion when he gets beat up. IG handle @kleinrunsdpt

Dr. David Salas is a 135 lb male with notable PRs ranging from 3:54 in the 1500m to 1:08:36 for half marathon. He typically runs 60 to 70 miles per week and trains from about 7:30 recovery runs to fast shorter efforts at 4:30 pace. He normally prefers neutral shoes with a firmer ride, but is completely open to other types of shoes.  He is a footwear enthusiast at heart and will always appreciate a high quality shoe when it comes around. For updates on training or testing, IG handle: @docsofrundavid

Dr. Brown is a 155 lb male with notable PRs of 18:18 5K, 39:25 10K, 1:29:01 half marathon, and 3:54 marathon. He typically runs between 20-40 miles per week at a variety of paces from 7:30-8:30 min/mile for recovery runs to 6-6:45 min/mile for tempo runs. He typically prefers shoes that provide some cushioning underfoot but still maintain a more firm and responsive feel. Current goals for 2020 are to break the 1.5 hour half marathon and 3:30 marathon. IG handle: @nate.docsofrunning

Editor's Note: As always, the views presented on this website belong to myself or the selected few who contribute to these posts. This website should not and does not serve as a replacement for seeking medical care. If you are currently injured or concerned about an injury, please see your local running physical therapist. If you are in the Los Angeles area, I am currently taking clients for running evaluations.

Doctor of Physical Therapy
Board Certified Orthopedic Clinical Specialist
Fellow of the American Academy of Orthopedic Manual Physical Therapists

Nathan Brown PT DPT MS
Doctor of Physical Therapy 
Masters in Anatomy and Clinical Health Science
Movement Performance Institute Certified in Advanced Functional Biomechanics 

David Salas PT DPT CSCS
Doctor of Physical Therapy
Certified Strength and Conditioning Specialist

***Disclaimer: These shoes were provided free of charge in exchange for a review.  We thank the  people at HOKA ONE ONE  for sending us a pair.  David also now competes for the HOKA Aggies for the 2021 year. This in no way affected the honesty of this review. We systematically put each type of shoe through certain runs prior to review. For trainers and performance trainers, we take them on daily runs, workouts, recovery runs and a long run prior to review (often accumulating anywhere from 20-50 miles in the process). For racing flats we ensure that we have completed intervals, a tempo or steady state run run as well as a warm up and cool down in each pair prior to review. This systematic process is to ensure that we have experience with each shoe in a large variety of conditions to provide expansive and thorough reviews for the public and for companies. Our views are based on our extensive history in the footwear industry and years testing and developing footwear. If you are a footwear rep looking for footwear reviews or consultations on development, we are currently looking to partner with companies to assist, discuss and promote footwear models. Partnership will not affect the honesty of our reviews.

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