Editor’s Note: I am tickled to offer this review of the Montrail Fluid Flex ST authored by Dominick Layfield. Road Trail Run also previously reviewed the Fluid Flex ST here. Dominick is one of the speediest trail and ultra distance runners in Utah. He runs 10-15 races each year, mostly in the 50-100 km range. He is often on the podium, including a fantastic 2nd place at the very tough Tushar 93K in Utah just this month. With many long trail races under his belt, he prefers agile light trail runners such as Nike Terra Kiger, Montrail Rogue Fly and Fluid Flex.
Dominick lives in Park City, UT. He holds a PhD in biomedical engineering from MIT, and has worked as a researcher in orthopedic biomechanics. So he knows the difference between a ligament and tendon :-).
Dominick lives in Park City, UT. He holds a PhD in biomedical engineering from MIT, and has worked as a researcher in orthopedic biomechanics. So he knows the difference between a ligament and tendon :-).
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| Dominick won the 2015 New Year's Day 5 Hour Run at the Utah Olympic Oval, running 39 miles! _____________________________________________________________________ |
Montrail FluidFlex ST
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| Montrail Fluid Flex ST |
Background
Ten years ago, trail running shoes seemed to be conceived similarly to hiking shoes: they were stiff and protective and heavy. I used to buy lightweight road shoes in order to get something that felt nimble and fast.
About the first actual ‘trail-running’ shoe that I liked was the Montrail Rogue Racer, which at the time seemed like a huge breakthrough in offering a remarkable degree of cushioning in a lightweight package. This was a ‘what’s not to like?’ shoe for me: it suited my foot shape, and did everything well. I think I went through three pairs of these, wearing them all till they fell apart. (I’m never one to retire shoes when they hit a particular mileage.)
When the original Montrail FluidFlex launched, it felt like another winner: this shoe was even lighter than the Rogue Racer, and offered a less structured upper, and an amazingly plush, cushioned forefoot. For me, this seemed like the Holy Grail. I loved the idea of an unstructured shoe that essentially consisted of a piece of foam underfoot to protect from rocks, and just enough upper to hold the sole in place.
I wore the FluidFlex in almost every training run, and many long races up to 100 km in length. For the most part, I felt that there was very little wrong with the shoe. It had a pleasing underfoot squishiness that -- although not to everyone’s taste -- suited me perfectly. It felt low to the ground, nimble, light, simple. Plenty of width in the forefoot, without being sloppy. Low heel to toe drop (4 mm). It performed nicely in pretty much every kind of terrain (including road running).
Some runners apparently had issues with the shape of the toebox, and this was something that Montrail tweaked in the (very similar) FluidFlex II. But otherwise, they wisely kept the changes mostly cosmetic.
One shoe can never be ideal for all conditions and distances, and I did find that the FluidFlex left my feet tired and sore after longer runs and rougher terrain. When I was preparing for the Bighorn 100-miler and ramping up my training volume, I reluctantly came to the conclusion that I simply needed more structure and protection for both the actual race, and for the high mileage that I was running in training. For the hundred, I switched to the Montrail FluidFeel, which was a more traditional, more supportive, heavily cushioned shoe.
Given that I loved the FluidFlex, but often wanted ‘just a little more protection’, I was pretty excited to hear that Montrail were producing a new variant.
Montrail FluidFlex ST
Two things are immediately apparent. Firstly, right under the forefoot (under the ball/crease of the foot) there is a new patch of stiffening material. I don’t know if this is considered a rock-plate, but it certainly provides a little extra protection from sharp rocks without noticeably compromising the trail feel and sensitivity that made the original FluidFlex such a winner for me. |
| Fluid Flex (left) Fluid Flex ST (right) |
Secondly, the rear of the shoe is substantially beefier and more significant than before. For some people, this may be a nice upgrade, but I really had no issues with the original shoe, and to my mind the shoe is now somewhat imbalanced, with the forefoot of a minimal shoe and the rear of something more substantial (similar to the FluidFeel).
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| Montrail FluidFlex ST |
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| Montrail insoles tend to lose their thickness over time. Old and new compared. |
I was disappointed, too, in Montrail’s choice of footbed. One of the few things that I found to criticize in the original FluidFlex and FluidFlex II was the footbed/insole. In keeping with the philosophy of the shoe, this is lightweight and minimal. The problem with it is that the foam compresses and loses its thickness over time. After a hundred miles or so of use, the thickness drops from ~4mm down to 1mm or less, becoming paper-thin underfoot. Consequently, the shoe feels more roomy, as if it has stretched out.
The FluidFeel comes with a thicker, heavier, Ortholite-branded insole that is excellent, and doesn’t seem to degrade with use. I pulled the Ortholite insoles from my FluidFeel shoes and transferred them to the FluidFlex ST.
On my first run, I liked the shoe immediately. It instantly felt comfortable and familiar. It has all the strengths of the vanilla FluidFlex and provides a little more rock protection. Like the FluidFlex, it feels great on both road and trail. After only a couple of test runs, I felt comfortable using the shoe in a long trail race (Quicksilver 100 km in California) in which I had no foot issues at all.
As far as the ‘stability’ aspect of the shoe is concerned (presumably this is the “ST” in “FluidFlex ST”), I’m on the fence. I don’t generally think I need or like ‘stability’ features in a shoe. In this case, the midfoot is augmented by what Montrail call their ‘FluidFrame’, which increases the torsional stiffness. This is combined with a more substantial heel counter, and slightly more built-up ring around the ankle. This may be a good thing for some people: if you have a tendency to heel-strike with your foot slightly off-angle, it may help straighten out your foot as the forefoot lands. Personally, I actually find it slightly disconcerting. When running fast downhill on uneven trails, you don’t necessarily want your heel to be aligned with the forefoot: if your heel lands on an off-camber incline, a torsionally stiff shoe will make the forefoot rotate to the same off-camber angle, which may make the trail feel more uneven and the shoe less stable. On the other hand, the shear stiffness of the ankle collar makes for secure footing during sudden changes of direction.
Despite my initial ambivalence (about the shoe forefoot and heel structures feeling slightly mis-matched), I’ve really liked the Montrail ST. According to Strava, I’m up to about 250 miles in them. I’ve worn them in several trail races, and in a ton of training runs. What’s most relevant is that I find myself reaching for them automatically: they live on top of my big bin of shoes, and have not been buried by newer, shinier models.
What would I change? Only little things. Firstly, Montrail need to fix the problem with their insoles losing volume. That seems easy enough. Secondly, I would thicken (or stiffen) the forefoot cushioning and maybe expand the rockplate coverage in order to bring the forefoot to a level of protection that is consistent with the relatively substantial rear.
I really liked the new, small rockplate under the forefoot. I think this is a useful upgrade and would like to see this carried across to the regular (non-ST) FluidFlex. Hopefully this will appear in the FluidFlex III.
The FluidFlex ST can be purchased from Backcountry.com at the links below. Purchases help support my site. Thanks!
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