Our verdict

True to its roots, the Carbon X 3 remains our trusty go-to for anything ultra-distance. It's packed and loaded with a carbon-fiber plate that makes it a highly stable and snappy ride. Even more, it delivers smooth heel-to-toe transitions that have made our long-distance runs bearable and easy. On top of this, it's everything you'd expect from a luxe running shoe. From looks to performance, it kills it!

Pros

  • Unobtrusive carbon plate
  • Responsive ride
  • Smooth transitions
  • Stable
  • Durable
  • Sock-like collar
  • Grippy

Cons

  • Loose-fitting knit upper

Audience verdict

80
Good!
  • Top 16% most popular running shoes

Who should buy

The Hoka Carbon X 3 is a super shoe that we believe is great for: 

  • marathoners who want to finish the race instead of setting PRs 
  • ultra distances in moderate tempo to faster paces
  • runners who want a smooth and easy ride during long runs
  • those who prefer a firm ride for training runs

hoka-carbon-x-3-on-foot.JPG

Who should NOT buy

The Carbon X 3 is a pass for runners who want a racer for short distances. It's on the heavier side; that's why.

If you want something fast and light for such a distance, consider the ASICS Metaspeed Edge+ (7.3 oz). And if you want the ultimate energy return from Hoka, go for the Rocket x2

Breathability

We found the knit upper's ventilation to be quite good. Our feet remained cool and dry even under warm weather. However, it is not the most breathable trainer on the market, receiving only 3 out of 5 in our smoke-machine test. Expect decent airflow but not on a hot summer day.

Hoka Carbon X 3 (left): it's breathable; Adidas Runfalcon (right): very little smoke is coming out, and only from the tongue area, so this shoe is not breathable. To make this test, we use a smoke-pumping machine and cover up the shoe mouth entirely so that the smoke can only escape through the upper.

The second test we carried out confirmed the previous results: we put the upper against light, and it clearly showed that is well-perforated, and therefore airy.

Test results
Carbon X 3 3
Average 3.8
Compared to 228 running shoes
Number of shoes
1
Breathability
5

Durability

Outsole hardness

Just like the Hoka Mach 5, the Carbon X 3 makes use of a firm rubberized EVA form at the bottom of its platform. While it helps to save the shoe's weight tremendously, it has consequences for its long-term durability.

hoka-carbon-x-3-outsole.JPG

Using a durometer to check the firmness of this layer, we got 64.5 HA. That's 25% softer than the road shoe rubbers on average! As soft as it feels upon landing, this compound is doomed to wear out much faster compared to a typical outsole rubber.

Test results
Carbon X 3 64.5 HC
Average 80.4 HC
We use an average of four tests. The photo shows one of those tests.
Compared to 279 running shoes
Number of shoes
52.1 HC
Outsole hardness
92.8 HC

Outsole thickness

Because there is no rubber outsole per se, we kept the outsole thickness at 0.0 mm. But if you're wondering how thick the rubberized foam layer is, our caliper showed 7 mm. 

hoka-carbon-x-3-outsole-thickness.JPG

Test results
Carbon X 3 0.0 mm
Average 3.2 mm
Compared to 298 running shoes
Number of shoes
0.0 mm
Outsole thickness
6.6 mm

Weight

We weighed the shoe on our scale, and it returned 8.4 oz (239g). That's a whole ounce lighter than average!

But, of course, if we compare it to speed training shoes only (8.5 oz/237g), the Hoka Carbon X 3 is right about average. 

Test results
Carbon X 3 8.43 oz (239g)
Average 9.35 oz (265g)
Compared to 299 running shoes
Number of shoes
5.26 oz (149g)
Weight
12.56 oz (356g)

Cushioning

Heel stack

Stack heights gone wrong! Officially, the Carbon X 3 has a heel stack height of 32 mm. However, we got a different result in our lab - 35 mm.

On one hand, that means even more cushioning (yay!), but the higher heel also affects the shoe's drop... More on that below.

hoka-carbon-x-3-heel-stack-height.JPG

Test results
Carbon X 3 35.0 mm
Average 33.6 mm
Compared to 298 running shoes
Number of shoes
7.6 mm
Heel stack
42.7 mm

Forefoot stack

The forefoot stack height actually turned out to be lower than stated: 24 mm over the official 27 mm.

hoka-carbon-x-3-forefoot-stack-height.JPG

Test results
Carbon X 3 24.0 mm
Average 24.9 mm
Compared to 298 running shoes
Number of shoes
7.6 mm
Forefoot stack
35.8 mm

Drop

The measurements mentioned above give us a heel-to-toe drop that is completely different from what the brand says. It's not 5 mm, but actually 11 mm.

Hoka Carbon X 3 drop

To understand why it's important to know the drop, consider that different drops affect muscles, tendons, and joints in different ways. Higher drops (8-14 mm) load more hips and knees, whereas low drops (0-5 mm) make calves and Achilles tendons work more.

So, if you are expecting a 5mm heel drop in the Carbon X 3, it is going to be a huge disappointment!

Test results
Carbon X 3 11.0 mm
Average 8.6 mm
Compared to 298 running shoes
Number of shoes
-0.8 mm
Drop
16.1 mm

Insole thickness

This Hoka has a thin insole. Our caliper showed 2.3 mm, while the average for running shoes is around 4.5 mm. 

hoka-carbon-x-3-insole-thickness.JPG

Test results
Carbon X 3 2.3 mm
Average 4.5 mm
Compared to 294 running shoes
Number of shoes
1.5 mm
Insole thickness
7.3 mm

Midsole softness

Note: a low durometer measurement equals a soft material, whereas a high measurement means it's firm.

The shoe's plate is not very stiff and the midsole is a touch more forgiving than the Carbon X 2.

It's true that the foam used in the midsole is soft. Actually, with a durometer reading of 19.0 HA, it is 26% softer than average. Yet, due to the presence of the plate, it is not an extremely soft shoe, it is balanced.

hoka-carbon-x-3-midsole-test.JPG

Test results
Carbon X 3 19.0 HA
Average 21.4 HA
We use an average of four tests. The photo shows one of those tests.
Compared to 226 running shoes
Number of shoes
8.5 HA
Midsole softness (soft to firm)
41.5 HA

Difference in midsole softness in cold

We put the shoe in the freezer to simulate cold weather conditions and found out that the midsole didn't change much. After 20 minutes, it became only 23.7% firmer, less than the average of 26.9%.

hoka-carbon-x-3-freezer-test.JPG

With a durometer measurement of 23.5 HA, it is 30% softer than the other "frozen" foams we've tested!

Test results
Carbon X 3 23.7%
Average 25.6%
Compared to 225 running shoes
Number of shoes
0%
Difference in midsole softness in cold
100%

Ride

Seamless would be the best word to describe the Hoka Carbon X 3's ride. Because of its meta-rocker, rolling forward felt effortless to us.

Thanks to the Hoka Carbon X 3's carbon plate, we felt supported from the first mile down to the last. Our feet and legs never felt strained while running in this Hoka shoe. This is also one of the reasons why we approve of it as a long-distance racer. 

Stability

Lateral stability test

Contrary to other speed-day shoes like the Nike Next% collection, the third version of the Carbon X felt a bit more stable. 

Torsional rigidity

We believe that the stability is mostly due to this Hoka shoe's torsional rigidity.

As our manual test shows, the carbon plate makes it very difficult to twist the Carbon X 3 sideways. On a 1-5 scale, where 5 is the stiffest, we gave this shoe a maximum score of 5.

Test results
Carbon X 3 5
Average 3.2
Compared to 277 running shoes
Number of shoes
1
Torsional rigidity
5

Heel counter stiffness

The shoe's heel counter, on the other hand, has much more give to it.

We gave its stiffness a low score of 2 out of 5, indicating that it's quite bendy and doesn't hold the ankle so rigidly.

Test results
Carbon X 3 2
Average 2.8
Compared to 261 running shoes
Number of shoes
1
Heel counter stiffness
5

Midsole width in the forefoot

The platform of the Hoka Carbon X 3 is neither wide nor narrow. It sits right at the average of road running shoes.

Measuring the widest part of its sole in the forefoot, we got 111.2 mm. That's even 2 mm narrower than average.

hoka-carbon-x-3-midsole-forefoot-width.JPG

Test results
Carbon X 3 111.2 mm
Average 113.7 mm
Compared to 299 running shoes
Number of shoes
100.5 mm
Midsole width in the forefoot
126.5 mm

Midsole width in the heel

The situation is better in the heel. Our caliper showed 90.1 mm which is precisely the average.

Hoka Carbon X 3 midsole heel width

Test results
Carbon X 3 90.1 mm
Average 90.4 mm
Compared to 299 running shoes
Number of shoes
74.9 mm
Midsole width in the heel
106.6 mm

Flexibility

Stiffness

The Carbon X 3 is a stiff shoe and we can prove it.

It required as much as 50.4N to bend the shoe in our longitudinal flexibility test. This is as much as 40% more than it takes on average in our lab!

On the other hand, these results also showed that this Hoka shoe is not as stiff as the other shoes in the carbon-plated category. For example, the Carbon X 3 is 66% more flexible than the Vaporfly 2!

Test results
Carbon X 3 50.4N
Average 29.1N
We use an average of four tests. The video shows one of those tests.
Compared to 281 running shoes
Number of shoes
2.2N
Stiffness
94.4N

Grip / Traction

On dirt, gravel, crushed rock, wet, and dry surfaces, the shoe bites.

Hoka Carbon X 3 outsole

Size and fit

Toebox width at the widest part

Based on our measurements, the shoe's toebox is much narrower than average! In the widest part of the forefoot, our caliper shows only 92 mm (6 mm narrower than average)!

hoka-carbon-x-3-max-width.JPG

But the trick is that the shoe's knit upper material is a damn stretchy one! From our experience, it can really stretch from narrow to medium fit!

Test results
Carbon X 3 92.0 mm
Average 98.3 mm
Compared to 299 running shoes
Number of shoes
89.5 mm
Toebox width at the widest part
109.1 mm

Toebox width at the big toe

The shoe's toebox also narrows down at the big toe. Measuring the width here returned only 70.9 mm which is over 6 mm narrower than average.

hoka-carbon-x-3-big-toe.JPG

If you need a high-end speed trainer that accommodates wide feet, try the Adidas Adizero Boston 12

Test results
Carbon X 3 70.9 mm
Average 78.2 mm
Compared to 173 running shoes
Number of shoes
60.4 mm
Toebox width at the big toe
92.5 mm

Carbon X 3 vs. 2: Toning down the aggressiveness

These are the most notable changes introduced in the Hoka Carbon X 3:

  • The new Profly X midsole offers a softer feel for a more responsive ride. 
  • For a more flexible wrap, a new knit upper is introduced.
  • The Hoka Carbon X 3 also loses 0.2oz (5g), from 8.7oz (247g) to 8.5oz (242g), while maintaining the same rubberized outsole and stack height.

hoka-carbon-x-3-shoe-in-pieces.JPG

Style

It makes a statement. With its huge stack, two-tone colors, and detailed knit pattern, it's hard not to notice the Hoka Carbon X 3. 

hoka-carbon-x-3-design.JPG