Nike ACG Ultrafly Review: Some Conditions Gear

Introduction to the Nike ACG Ultrafly

TAYLOR: Leave it to Nike to light the lava flow for the current eruption of trail running. They’re all-in on the outdoors, bringing back the adventure-oriented All Conditions Gear (ACG) sub-label with every ounce of marketing energy they got. It’s been overhauled and released into the wild, bringing back that rugged and feral energy that made it an icon to begin with, nearly 35 years ago. 

The relaunch coincided with the 2026 Winter Olympics, as athletes and coaches alike sported ACG-branded parkas, caps, and apparel. The gear looks good– really good. But gear only goes so far if it doesn’t work in action. And as far as performance goes, it all starts with the Nike ACG Ultrafly.

A pinnacle race shoe that has already seen victories at Western States 100 and a slew of other podium finishes, it features a ZoomX midsole, carbon fiber Flyplate, and Vibram Megagrip outsole. The midsole formula has been tweaked since the first version of the shoe (the similarly named Nike Ultrafly) and the cordura-like wrap that encased the midsole in the first version has been trimmed back. It also features an all-new Vapormesh upper material and a 7/8-length carbon fiber plate.

After getting miles in the Nike ACG Ultrafly it’s no surprise that Nike pro Caleb Olson used this tool for the specific job of winning Western States.

I will say no more… until the next section, anyway.

REESE: The Nike marketing and product teams have had a busy few years. I’ve been impressed with their marketing and investment into the trail scene, and I’d be lying if I said I wasn’t anxiously awaiting the release of this shoe. The hype. My god, the hype. So much. The bold color choices. The incredibly noticeable ACG Radical Airflow warm-weather top. It’s hard not to see Nike when they show up somewhere. They’re not exactly subtle in letting the trail scene know that they’re here and here to stay. 

It feels like the Nike ACG Ultrafly is the firstborn, saddled with massive expectations of carrying the ACG legacy forward. But can it? Did it? Well, sort of?

What we like about the Nike ACG Ultrafly

TAYLOR: The ZoomX midsole is where I’ll start. It’s a magical foam that has literally altered the courses of performance shoes over the years, beginning in the Nike Vaporfly 4% and working its way down the line and across the board. That said, not all ZoomX is the same. Yes, the chemical composition is consistent, but the durometer (i.e. softness) fluctuates depending on the shoe and its desired purpose. 

The good news? It’s just as luscious here. The softer Flyplate (compared to the first version) wasn’t very apparent during my first run. After about 15 miles, I really started to feel the update and the subsequent ZoomX goodness that came along with it.

I’ll hold off on my notes regarding the plate and its limiting effect on the foam. At the same time, I can’t argue with the soft and bouncy nature of the ZoomX that eked out a little more every time I ran in it. 

In fact, the combo was extremely effective on smoother terrain. I often would check in with my effort, then my watch, and realize I was cruising quicker than I perceived. This is the type of efficiency that has become so crucial in these ultra-distance race day options. Admittedly, I hoped for more excitement. However, I can’t deny the obvious performance output when wearing the shoe. It is one of the best examples of uni-lateral efficiency on the trails. It landed between the sensation of the Asics Metafuji Trail and Puma Deviate Nitro Elite Trail in that sense. 

A touch of stability is noticeable in this shoe, and most of it comes from the aforementioned stiffness of the Flyplate. It helped counter some of the softness and energy that came directly from the ZoomX foam in the heel and midfoot. For better or for worse, it resisted torsional flex– some will really appreciate that while others may not. 

The forefoot provides stability, but in a more natural way. For starters, the forefoot rocker is a bit less extreme than many other race day options. Also, an engineered mesh overlay wraps around the forefoot’s foam, encasing it and moderating it. Those facts, in conjunction with a slightly broader-than-typical-Nike forefoot, allowed for a really pleasing toe off.

Up top, a technical engineered mesh with strategic topographic-like mesh overlays, structured/padded heel counter, and a bomber gusseted tongue create a beautifully fitting and durable package. It’s going to be a slimmer fit throughout, but I could slip in fine, even with my wider forefoot. The shape of the forefoot is less “round” than the previous version. Personally, I found it to be marginally slimmer than before. That’s sure to please those who enjoy the Vaporfly and Pegasus for the roads. 

Breathability was fine during cooler temps. Warmer weather and the wrong sock can make this one feel a little steamy. Perforations in the sides of the upper, as well as a softer tongue, allow for some breathability.. 

As always, Vibram Megagrip provides a tacky rubber outsole. This is virtually the same outsole as the previous version. The best application is dry packed surfaces because the lugs are so shallow. That does make them quite versatile for the road-to-trail scenario.

REESE: Looking at its tech sheet, the Ultrafly really has all my favorite ingredients. Just a shoe built for speed. Carbon plate, Vibram Megagrip. Engineered upper. Looks fast as hell. And indeed I do like a lot about this shoe. It seems that Taylor and I had, yet again, a similar experience with this shoe. 

I’ll start at the bottom. I love when a shoe uses Vibram Megagrip and trusts that it’s going to give you– yep– mega grip on technical surfaces. The lugs are on the smaller side, which I actually appreciate. I found that the stickiness of the Megagrip makes up for the smaller lugs. So while I wouldn’t recommend scrambling on class five easy routes in these, if you’re in the Ultrafly and you’re trying to go fast (or at least feel fast), the outsole provides just enough traction without slowing you down. It definitely shines on smooth singletrack and lightly technical trails. I’ll go into why that is in the next section.

I felt like the fit was mostly a good thing. In the past, I’ve always worn a size W7 in Nike, but the W7.5 fit me well. Visually, the shape of the shoe told me I’d like this fit. Picture an unbalanced figure eight, with the top of the eight wider than the base. To me, that means a slightly roomy toe box, a stable forefoot landing zone, and a snug midfoot and heel. I had just a little room between my toe and the front of the shoe.

The toe box has enough room to splay my toes and accommodate the foot swell in longer races or runs. My midfoot was comfortably snug and supported by the gusseted tongue. The heel was not perfect, but if you like a cushioned heel cup, you’ll love the Ultrafly. 

The Ultrafly did feel shockingly stable for a shoe with an 8.5 mm drop. I’ll go into this a bit in the next section, but I was skeptical of how this shoe would perform on uneven, off-camber, and technical terrain. I trusted that the Vibram Megagrip would keep me glued to the ground, but it can only do so much if the rest of the shoe is built wrong.

During testing, I took this shoe out on runs that went from road to trail, on smooth singletrack, up and down technical and loose rocky descents. And while it was okay on the loose descents, it’s not perfect. For most fast nontechnical courses, I can see this shoe doing exceptionally well. In fact, I’m pretty sure I saw the blaze orange of this shoe on many runners at Black Canyon 100k. They seemed to be doing just fine in it. And that course is a great application for it.

What we don’t like about the Nike ACG Ultrafly

TAYLOR: I’m letting the cat out of the bag to run around and scratch things up in its hissy fit. Wait– I might be the cat in this scenario. 

There are some real things to love about the Nike ACG Ultrafly. There are also many points of contention here. 

The biggest issue, for me, came from a combination of specs. That combo of the very stiff Flyplate and higher drop seem to be the culprits. While the Flyplate performed wonderfully in a straight line, it had a very hard time doing the trail tango. It reminded me of the early days of incorporating road-style plates for the trails (i.e. Saucony Endorphin Edge). There wasn’t enough flexibility for the plate to function as an active stability mechanism (though it did so passively), and it would shoot you in whatever direction pressure was applied. If I stepped slightly off-camber, the shoe would launch in directions that counteracted my motion. This was simply annoying and uncomfortable at times.

This also created a lot of tension in the arch and midfoot area that left me surprisingly sore after runs here in the Rockies. If I were to stick to mellow stuff (i.e. non-technical trails or gravel), it really wasn’t too noticeable. 

Naturally, a slimmer fit won’t be for everyone. That’s not necessarily a negative; however, there are a lot of folks who consider this a must-have shoe and may sacrifice the squeeze for the sake of running in the Nike ACG Ultrafly. Perhaps a wide option would please the masses? Not Nike’s forte, but one can dream.

Lug depth will also fall into this category. While it is a versatile option for the road-to-trail scenario, my technical trails demanded more clawing action. It was the softer terrains of sand, mud, and snow that really felt lacking.

REESE: As I said above, when I first saw the ACG Ultrafly and looked up all the stats and materials, I assumed it was going to be my next favorite shoe. All the ingredients would surely make something wonderful. But after logging my first few runs in this shoe, I found myself texting Thomas and Taylor to see if they were having issues with the shoe. I was in disbelief that it could be anything other than awesome. I suspected it’s either me or a sizing issue. But alas, it seems that Taylor and I had a pretty similar experience with this shoe. Which is, we wanted it to work, we wanted it to be our favorite shoe, but it fell a bit short. 

For me, the most noticeable thing that I didn’t like– or maybe the first thing I noticed– was the lack of heel security. I was never able to lock down my heel. It wasn’t atrociously bad, but it was never solidly secure. Always rising ever so slightly on the flat and a bit more on climbs. I love a narrow, snug heel, with just a bit of soft padding for comfort; however, this just didn’t provide a Goldilocks fit. For some people, I’ve heard this heel works, but I’d wager if you’re anything like me, with a pretty low volume foot and narrow heel, this might be a little loose. Maybe just wear really thick socks.

The midsole seemed like it was going to be amazing, but due to the full-length carbon plate, I had a lot of issues with the stiffness of this shoe. In fact, I actually got super sore and had to detox from the shoes for a week to let my calf muscles calm down. The stiffness was most noticeable to me on the uphills. The carbon plate is so stiff that my arch and calf did extra work, so much so that my foot was actually in pain on uphills. I felt the calf tightness post-run. On the descents, the 8.5 mm drop, loose heel, and the carbon plate definitely had me going slower than normal simply because I felt unstable. The shoe wants to go fast, but I do not.  Like Taylor, I felt like the carbon plate had different ideas about which direction my foot should go if it hit a rock at the perfectly wrong angle. 

One thing that really drove me nuts was the insole. Most insoles are either just placed in the shoe or lightly glued in. Not so in the ACG Ultrafly. Nike slathered on the glue. I wear supportive inserts in my shoes, so I remove the insoles. It took me an hour to remove two insoles. I used chemicals, pliers, razor blades… you name it. I was sweating trying to get those things out. I don’t care what the material is or how fancy the insole is; give people the opportunity to switch it out easily. The Norda 005 has Arnitel TPEE insoles, and they provide another set for race day. Expensive? Yes. Easily removable? Yes. Come on, Nike.

Final thoughts on the Nike ACG Ultrafly

TAYLOR: When it comes down to it, I’m really quite torn on the Nike ACG Ultrafly. I desperately wanted to L-O-V-E this thing, but I just didn’t for most trail running scenarios here in the Rockies. 

Don’t get me wrong, the Nike ACG Ultrafly was an absolute monster on smoother terrain. I can see it being an easy choice for many running buffed out trails and the door-to-trail scenario. The more miles I put into these shoes, the more I loved it in this specific arena. 

It was when the trails turned it up a notch that they lost their luster and revealed a lack of attention to these demands. Everything about this shoe is oriented toward smoother trails. At the same time, it is marketed as your trail racer for “Less to Highly Technical” terrain. Then there’s the whole All Conditions Gear nomenclature. Talk about toxic positivity! It’s simply not true that this shoe works great on technical terrain, and my hands are tied because I have to weigh it against Nike’s claims. 

At the end of the day, if you’re looking for a race day option to pull you through anything from a 5k to 100 miles on relaxed terrain, I wouldn’t argue with anyone choosing the Nike ACG Ultrafly. But– if you’re not used to a slim fit or high drop or the demands of a rigid energetic plate, be weary. Okay?

REESE: Marketing is a hell of a drug. And Nike is perhaps the biggest dealer in the shoe makin’ world. I mean, utilizing the bright NIke orange palette alone is intentional marketing. They’ve done this before with hot pink and lime green Vaporflys and Alphaflys, an obvious way to stand out amongst all other shoes in the start corral. 

It signals speed and boldness. Ultraflys just everywhere. And I wanted to be a part of the in-crowd. I wanted this shoe to be my next favorite race day shoe for any race, any distance… for all conditions, as their marketing so boldly says. However, I haven’t found myself reaching for it since finishing up my miles in it. Perhaps it’s because I was so sore after the first few runs. But I think it’s because in a world where so many shoes can be the perfect choice for almost any race or condition (looking at my favorites: Norda 005, La Sportiva Prodigio Pro, The North Face Vectiv Sky 2), when I compare the Nike ACG Ultrafly to my favorites, the ride or die shoes that truly can do it all, this shoe just can’t compare to them. 

If you’re a road runner or used to the high stack, these shoes will likely hit the spot, and you’ll be hooked. I’m a low-stack kind of gal. I’d love to see Nike come out with, I don’t know, a SubUltrafly. Slim down the midsole heel, cut out a lot of the carbon. That’s my perfect shoe for all conditions. 

Had Nike not said so loudly that this shoe would be for all conditions, but instead had said this is a light trail or gravel racer, I believe I would have found this shoe to be ranked higher, but if comparing like to like, it falls short of expectations.

You can pick up the Nike ACG Ultrafly for $260 at nike.com by using the buttons below.