Inov8 Trailfly Zero review

The Inov8 Trailfly Zero caters to the trail runners who:

• look for very grounded and natural-feeling zero-drop shoes with a low profile
• have wide feet or prefer extra space in a rounded foot-shaped toebox
• like the idea of added shock absorption in a low-stack and lightweight shoe
• need reliable grip on rocks and mixed terrain

The Traifly Zero feels most at home on rocky and hard-packed terrain, but if you frequent soft terrain, deeper mud, and bog-like conditions, you will be better off with the brand's Trailtalon Zero.

And if you feel like you could use a bit more support and padding in a low-stack, zero-drop shoe, check out the Altra Lone Peak 9 instead.

The Trailfly Zero packs less cushioning than the standard Trailfly, but we found its impact protection to be surprisingly high for such a low-profile trail shoe!

With shock absorption readings of 107 SA in the heel and 101 SA in the forefoot, it dampens the impact of hard and rocky trails much better than the similarly built Altra Lone Peak 9 (96 SA and 82 SA, respectively). And it does so without compromising the ground feel.

This made us feel more inspired to go that extra mile in the Trailfly Zero!

The Trailfly Zero employs the same nitrogen-infused Flyspeed Pro midsole foam and the same eTPU Boomerang insole as the Trailfly Max. This power combo looked very promising on paper, but alas, our lab tests showed that the shoe's energy return is only average.

At 53.7% in the heel and 56.4% in the forefoot, there is some rebound to this Inov8 shoe, but it doesn't feel particularly propulsive or speed-enhancing.

As the more grounded option from the Trailfly series, the Trailfly Zero showed its slim-soled nature in our caliper measurements.

With a heel stack of 24.9 mm, it is significantly lower than the Trailfly (30.1 mm) and the Trailfly Max (37.1 mm). You can see the difference between the Zero and the Max platforms in the photo above.

Given the shoe's zero-drop design, it makes sense that its forefoot stack came in at nearly the same measurement of 24.4 mm.

That way, the Inov8 Trailfly Zero is only half a millimeter away from the perfect 0.0 mm drop.

However, we can forgive that minor discrepancy because, on foot, it feels like a true zero-drop shoe without a doubt. With no elevation in the heel, the foot remains parallel to the floor in the Trailfly Zero, promoting a more natural movement and engagement of the muscles and tendons. It caters to runners with forefoot and midfoot striking patterns.

But on the downside, a zero-drop shoe can put too much stress on the Achilles and calves, especially in beginner runners. An adaptation period is a must if you are new to this offset.

Pressing our durometer against the shoe's Flyspeed Pro foam, we found it to be on the firm side, just like in the Trailfly Max.

It's nowhere near as plush as the supercritical foams from other brands. With an above-average reading of 27.5 HA, it comes very close to the firm range of cushioning foams, by our standards.

But given the shoe's intent and low-stack setup, a firmer foam only makes sense for ground feel, stability, and underfoot protection from rocks and debris.

The Trailfly Zero's nearly flat, non-rockered geometry further enhances the shoe's natural ride.

It helps you feel more connected to the different surfaces beneath the foot, making the ride more controlled on changing and unpredictable terrain.

We bet you wouldn't be able to balance on a rock or on a downed tree as effectively in an aggressively rockered shoe.

Since introducing its NaturalFit in 2024, Inov8 has joined Altra and Topo brands in the making of foot-shaped options for trail running. And the Trailfly Zero is one of them.

Having created a mold of the shoe's interiors using custom gel, we were able to measure the Trailfly Zero's precise forefoot dimensions with a digital caliper.

The widest part of the shoe turned out to be a smidge short of the wide range at 97.7 mm, but it still proved to be wider than average. And if you need even more internal space, the Trailfly Zero is readily available in a wide version as well.

The toebox, on the other hand, proved to be exactly as wide as it looks on the foot.

Measuring its width in the big toe area, we got a nice and high reading of 78.1 mm!

It may not be as mind-blowingly wide as the Altra Lone Peak 9 (85.3 mm) or the Altra Superior 6 (82.4 mm) in its medium width, but you can opt for the wide version for that extra space.

Despite a thick rand around its toebox, the Trailfly Zero's vertical space proved to be fairly accommodating.

Our caliper recorded a standard toebox height of 28.0 mm in this Inov8 shoe. We experienced zero pressure points here!

According to our caliper measurement (3.4 mm), the Trailfly Zero's lugs lack just a little depth to match the promised 4 mm.

But gladly, this didn't affect the shoe's gripping capacity on mixed terrain. Its multi-directional tread pattern tackled dirt, grass, roots, rocks, moss, and light mud very effectively.

Inov8 mixes poitier chevron lugs for improved bite on ascends and descends, and smoother blocky ones for effective contact with hard-packed trails and rocks.

If you need a shoe for softer, muddy, and bog-like terrain, the Inov8 Trailtalon Zero would be much more suitable with its 6 mm studs and a more spaced-out lug design.

Given its low stack, the absence of a rock plate, and no heavy upper overlays in the forefoot bending area, the Trailfly Zero turned out to be a super flexible trail shoe.

As our shoe stiffness tester confirmed, this Inov8 shoe requires a force of mere 7.7N to bend by 30 degrees. Not only is it twice as flexible as the average, but it is even bendier than the Altra Lone Peak 9 (12.0N)!

Even though it's not that much lighter than the regular Trailfly (9.9 oz), the Trailfly Zero is still lighter than the average trail running shoe in a men's US size 9 (9.4 oz/266g).

We also found the shoe to be lighter than its close competition from Altra, the Lone Peak 9 and the Superior 6.

The air mesh upper on the Trailfly Zero looks nice and airy, but unfortunately, the smoke billow in our breathability test turned out to be not as thick and quick-rising as we expected.

Even though no thick overlays are blocking the shoe's ventilation on top of the toebox, and the material looks transparent...

...there is something about the weave itself that holds it back from letting the air in and out so effortlessly.

Because of that, we kept the Trailfly Zero's breathability score at a moderate 3/5.

As a low-profile shoe that feels minimalist-ish, the Inov8 Trailfly Zero is devoid of any additional arch support or stabilizing components.

And yet, we wouldn't describe it as an unstable shoe because its grounded nature makes it feel inherently stable.

The shoe also draws a good amount of support from the slightly raised midsole topline and the thick Met-Cradle overlays around the heel and midfoot. The latter tighten up to enhance support when the laces are cinched.

Taking the Trailfly Zero through our manual twisting test, we couldn't believe how little torsional rigidity it had! Rating its stiffness with the lowest possible score of 1/5, we found it equally pliable as the Merrell Trail Glove! 

This is as flexible as a trail shoe can be without entering the minimalist category!

The Trailfly Zero's minimal approach also touched the heel counter, which easily yielded to our pushing and squeezing. We rated its stiffness as low as 2/5.

This lack of structure offers little support in the rearfoot, which could be a problem for runners relying on a more secure lockdown around the heel and ankle. Lock lacing is very likely to be necessary here.

Designed for navigating rocky ascents and descents swiftly, it is only reasonable that the Traifly Zero is built on a slimmer platform.

Even the widest part of its base returned a below-average reading of 108.8 mm in the forefoot. We can confirm that it makes the ride more maneuverable without compromising stability.

The widest area of its heel came in at 82.8 mm, which is also significantly narrower than average.

There is no chunky rearfoot material to hold you back when agility is required, and that's what the Trailfly Zero was built for in the first place.

The Inov8 Trailfly Zero features a tough synthetic rand around its toebox perimeter. It is quite wide and covers a significant portion of the shoe's upper, except for the top of the toebox, where our durability test is always performed for consistency.

But having applied our Dremel to the shoe's exposed air mesh, we were pleasantly surprised with the result. Sure, it wasn't the sturdiest of materials, but it got away with a scuff instead of a full-blown hole! That kept the shoe's toebox durability at 3/5.

The mesh lining inside the shoe also held up decently under pressure, earning a moderate score of 3/5. Although we did wish for a better result, given the shoe's price point.

The outsole, however, was not a disappointment at all!

The brand's acclaimed Graphene Grip (G-Grip) rubber proved its worth in an 18-second Dremel encounter. The tool left a mere 0.7 mm of dent in the material, which is a little less compared to the average of trail running shoes.

Lug depth excluded, the Trailfly Zero's outsole thickness comes in at only 1.4 mm. It is thinner than average but contributes to the shoe's flexibility in return.

If you are familiar with Inov8's Boomerang insole, you will be treated to one in the Trailfly Zero as well. Made of numerous expanded TPU beads, its thickness exceeds the average at 6.1 mm in the heel.

It is pretty easily removable...

...but we would think twice before replacing it with a custom orthotic, as the insert is responsible for part of the shoe's energy return and comfort.

Not to mention its unconventional shape that matches the wide and rounded toebox of this Inov8 shoe.

If you happen to choose this Inov8 shoe for colder months, be prepared for the fact that its moderately firm midsole will get even firmer in cold temperatures.

Repeating the durometer measurement after a 20-minute freezer test, the HA reading went up to 34.0 HA, implying that the hardness increased by 24%.

In the absence of reflective elements, this Inov8 shoe offers zero visibility in low-light conditions.

The in-shoe padding is very minimal in the Trailfly Zero.

It features just a touch of foam to prevent rubbing and hot spots, and its tongue thickness measures only 4.0 mm.

A semi-gusseted tongue inside the shoe works together with the external Met-Cradle overlays to create a very secure midfoot hold.

The Inov8 Trailfly Zero is more expensive than the similarly built zero-drop trail shoes from Altra and Topo.

However, we believe that its price point can be justified by the use of Inov8's advanced nitrogen-infused foam, which offers more shock absorption per millimeter of stack compared to standard foams, all while keeping the shoe's weight pretty low.

A sturdy finger loop at the back of the collar helps with the on-and-off.