Hoka Carbon X 3 review

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

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. 

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.

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

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.

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!

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.

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%.

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

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

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. 

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)!

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!

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.

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

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

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.

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.

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.

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

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!

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. 

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.

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.

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.

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. 

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

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.

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.