Article by Mike Postaski
NNormal Kboix ($240 - includes 2 midsoles)
Introduction
Mike: The Kboix is obviously an interesting shoe due to the form factor. A “component” based design, with swappable midsoles - of different composition. In most cases, a design such as this might be written off as too experimental, and perhaps that still may be the case. But having Kilian involved, with him testing the shoe during his Alpine Connections project last year - certainly gives some credibility to this project. But Kilian is of course, Kilian - and there are many questions as to whether or not this is a functional design for the rest of us.
Pros:
Sustainability factor
Novelty of having different midsole feels
Replaceability of worn out midsoles down the road
Cons:
Different elements of shoe feel disconnected
Midsole sidewalls can cause irritation
Heel hold is sacrificed to allow easier midsole swapping
Feel very bulky on the run - weight is high
No bounce or response with either of the midsoles I tested
Flat feeling on the run
Squeaking sound if you go through water
Most comparable shoes
Speedland GS platform shoes (TAM, PGH)
Stats
Sample Weights:
men’s KB2 / Reactive (TPU) 11.6oz / 330g US 9.5
KB3 / Bounce (PEBA) 11.9oz / 336g US 9.5
Stack Height: 33mm heel / 27mm forefoot
Platform Width: 84mm heel / 66mm midfoot / 123mm forefoot
First Impressions, Fit and Upper
Mike P: The first impression out of the box is that the shoe is certainly very bulky. It certainly does not give off a streamlined look with its all black look and especially with the outsole rubber wrapping up and over the bottom edges of the shoe. It honestly looks like a work shoe more than a running shoe.
I went with my typical true-to-size US 9.5 which I also have the Kjerag V1 in. I find sizing length-wise to be roughly the same - plenty of space in front of the toes. I know some do size down in NNormal, which I could see, depending on how you fit your shoes. Definitely do not size up.
But the similarities end there. The volume inside the shoe I found to be especially low - with the vertical height over the top of the forefoot and toes noticeably low. It’s quite a difference from the roomy and toe-wiggly toebox of the Kjerag. After running in the shoe, I got the sense that this was one of the areas where they had to really make sure that the foot & midsole was securely strapped down - given the inherent nature of a separate midsole insert.
Midfoot hold is food - for me. Some fine NNormal shoes are too tight at the midfoot, but I like that secure feel, it’s the same here in the KBoix. Matryx uppers typically work really well for me but I think there’s just limitations with the design and shape of the shoe that don’t allow the Matryx to really stand out as a feature. Of course durability is the main factor in going with Matryx here.
Another area of concern is the heel. The rear heel tab is overly soft, padded, and flexible. They definitely made accommodations here - loosening up this area so that the midsoles could be removed and wedged back in.
This leads to very loose heel hold, and I definitely go with lace locking for these. The lace locking helps, but it’s not ideal as it just feels like my foot needs to be strapped down in all areas from the front to the back, in order to get a decent fit and foothold.
Midsole & Platform
The Kboix comes with two midsoles which you choose when purchasing. I received the KB2 (Reactive) which is TPU, and the KB3 (Bounce) which is PEBA. They also offer a softer KB1 which is supercritical EVA. The naming is somewhat confusing to me, and I kept getting mixed up because I typically associate “Bounce” with TPU, given the proliferation of beaded TPU midsoles that are just that - bouncy.
[weight without any midsole!]
It could be just semantics, but in my mind, I would typically assume PEBA is more reactive than TPU, but oh well. It’s a bit difficult to find much difference between the two midsoles. There’s so much going on with the shoe, between the upper fit, kind of a flat feeling ride (see ride section below), and the midsoles being wedged inside the shoe.
[add the midsole weight to the shoe “shell” weight]
With the weight being so (surprisingly) high for both midsole variations, I honestly didn’t get any sense of either “bounce” or “reactivity” from either. I did some test runs where I swapped mid run, and ran with different midsoles in each shoe, and I did prefer the TPU. I think it just felt a bit softer, and with the upper really squeezing my foot down from above, the softness just seemed to conform a bit more and give a touch more comfort.
Outsole
Outsole is Vibram Megagrip, in a similar lug shape and configuration as the Kjerag V1. Wide, flat lugs at a depth of 3.5mm. They don’t give the best bite, but the broad, flat design should make them more durable than narrower, angular lugs. That of course matches the intention of the shoe as the outsole is supposed to last through several midsoles (at least the two that come with the shoe).
The platform is on the wider side, again making accommodations because the rubber itself needs to extend up around the bottom of the shoe and be stitched directly to the Matryx upper. 123/66/84mm is what I measured for my US 9.5. 123mm under the forefoot is quite wide - matching the Adidas Terrex Speed Ultra which has a massively wide forefoot platform for stability.
I do think the outsole hinders the ride a bit, because the side parts (not just the rubber under the foot) also need to flex. This certainly hinders flexibility, as there are no flex points designed into the outer edges. It just needs to kind of fold into itself as the shoe flexes.
Ride, Conclusions and Recommendations
The ride overall feels “flat” to me. I already talked about the pretty wide platform, but also given the general design - it’s pretty difficult (near impossible?) to add any type of rocker into the shoe. With the midsoles removed, the outer upper/outsole combo is essentially a flat slab. I don’t see how you could possibly give it much shape to enhance the ride a bit.
On the run, it feels like plodding along - especially given that it’s really at the upper end of the weight range in my sizing. I’ve run in shoes at a similar weight or even a touch heavier that do feel much more runnable. It just feels like a struggle to get the shoe to flex and give any kind of dynamic feel.
At Sam’s advice, I ran through a bunch of streams and even let them soak for a bit to see if they would loosen up in any way. This just introduced a squeaking sound between the midsole and outsole that was highly annoying. During most runs I noticed the same annoying rubbing sound and I could even feel it underfoot - the midsole and outsole flexing and rubbing against each other.
The sidewalls of the midsoles were the primary issue for me - and actually made me shelve the shoe for a while. The midsole needs to have sidewalls in order to securely seat it inside of the shoe. These sidewalls really rubbed the front edges of my foot around the arch. Some shoes do implement a sort-of bathtub design, but in those cases the midsole usually wraps up along the exterior of the shoe. Here the higher midsole edges are right up against the foot.
The KBoix, for me, is an interesting experiment, and could possibly have use cases such as hiking or maybe slower training. You get two midsoles included, so presumably, given the durability of Vibram outsoles, you could get double the miles out of these? Then purchase additional replacement insoles when those wear out?
I honestly didn’t venture too much into technical terrain in these. The aforementioned sidewall irritation was again the big factor there. I would notice that irritation right away on my runs, and then I was reluctant to venture too far in them. The runnability for me is lacking compared to standard running shoes. There are just too many accommodations that are made to make the modular design passable. I really struggled choosing to run in this shoe - when there are so many solid options out there.
Mike P’s Score: 6.83 / 10
Ride: 6 - You can get them going, but it takes some work
Fit: 6 - Loose heel, low volume, too strapped down
Value: 8 - That’s the proposition here, but good if you can find usage for them
Style: 6 - More like a work shoe than a running shoe
Traction: 8.5 - As good as the Kjerag
Rock Protection: 8.5 - Stack is ok, but a lot of flex underfoot
Smiles 😊😊
3 Comparisons
Speedland GS:TAM/PGH (RTR Review)
(US 9.5): Similar in that the Speedland shoes have a drop-in midsole. But the Speedlands also have a lower midsole layer that is integrated into the outsole/upper “shell”. This setup gives a much better connection between the separate elements, and works like a normal running shoe. The TAM was quite heavy, but the PGH did drop some weight. Both Speedlands have a more runnable geometry and for me fall into the category of running lighter than their weight. The Speedlands are notoriously high volume (I’ve learned to actually size down with the PDX), while the KBoix is the opposite - quite snug relative to their platform.
Brooks Caldera 8 (RTR Review)
(US 10): The Caldera 8, on its own, feels like a massive shoe, but it still comes in about a half ounce lighter than the Kboix/midsole combo. It also sports a wide ground platform - wider at the midfoot/rear than the Kboix, but the Kboix is wider under the forefoot. The Caldera feels somewhat flat in terms of arch support and on landings, but it does turn over decently well. It feels like you have to work so much more to turn over the Kboix.
Topo MTN Racer 4 (RTR Review)
(US 9.5): V4 gained some weight and lost some flex, which I did not like. But putting it up against the KBoix, it does stack up well, with a similar sort of flat and heavy-ish feel on the run. The Topo is again narrower under the forefoot, giving it a more agile feel in comparison to the KBoix. Foot comfort is no comparison as the Topo’s signature midfoot hold plus foot shaped toebox is much more comfortable.
Index to all RTR reviews: HERE
Tester Profile
Mike Postaski currently focuses on long mountainous ultras - anywhere from 50K up to his favorite - 100M. 5'10", 138 lbs, midfoot/forefoot striker - he typically averages 70 mpw (mostly on trails), ramping up to 100+ mpw during race buildups. A recent 2:39 road marathoner, his easy running pace ranges from 7:30 - 9:00/mi. From 2022-23 Mike has won the Standhope 100M, IMTUF 100M, and Scout Mountain 100M trail ultras, winning the Scout 50M in 2024. He also set a CR of 123.74M at the Pulse Endurance Runs 24H and completed the Boise Trails Challenge on foot in 3 days 13 hours, besting the previous record by 7 hours. Mike's shoe preferences lean towards firmer, dense cushioning, and shoes with narrower profiles. He prefers extra forefoot space, especially for long ultras, and he strongly dislikes pointy toe boxes.
Europe only: use RTR code RTR5ALL for 5% off all products, even sale products
No comments:
Post a Comment