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Fox Union (double!) BOA Flat Shoes

Photos Deniz Merdano
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Fox Racing launched a mountain bike shoe line in February of 2023. I suspect they either hired or already employed the right people because their entry into this challenging and contested market has been smooth. The shoes look good and have been generally well received. I hadn't tried any until this pair of Union BOAs arrived and I was skeptical, as I always am about new players in the flat shoe market.

So many things can go wrong with a flat shoe. Grip is the big thing companies mess up, which I attribute to a lack of awareness of the market. Many people who work in the mountain bike world haven't ridden flat pedals since they were kids and it seems to me they often underestimate the challenges involved in making good flat pedal shoes. We have had shoes arrive with too much camber in the forefoot, a hard raised arch in the outer sole of the shoes, too much flex, not enough flex or protection and, most often, not enough grip. There are many ways to screw up flat pedal shoes and it happens regularly because some companies seem to think, "we're just making a sneaker."

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If you are looking for the highest grip possible, Fiveten remains the king. If you prefer to be able to reposition your foot without sitting down, these might hit the spot.

A leg up Fox has over most other players in the flat shoe market is 50 years of experience making boots for moto. Obviously the parallels aren't perfect but grip is important for moto and riders are undoubtedly fussy like mountain bikers. Knowing how to do something right, after years of practice, is a transferrable skill.

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About twenty rides in and these aren't showing signs of wear. Just signs of dirt.

Fit/BOA Li2

These are a little on the small side. I tried the lace up version locally before I replied with a size request and the 44.5 seemed to work best. A proviso is that I have to wear thin socks and even then these are a little snug, which works great for me. The sizing guide suggests the North American size equivalent is an 11 but to me it feels more like a 10.5. Width is fine and while I don't have extremely wide feet, I regularly find some shoes too narrow. I'd call these moderately wide if that is any help at all. The toe box is an average size and heel hold is good despite my narrow ankles. The BOA Li2 dials allow a micro-adjustable fit; the Li2 designation indicates that these are the more expensive two-way BOA dials. To remove your shoes, you still pop the dials out but if your shoes feel a little tight you don't have to start from scratch. Just turn them counter clockwise and they will release proportionally.

A concern is the BOA only system. If your lower BOA fails you'll probably be okay but if the upper one goes south it won't be ideal. If you lose both there is no back up. I like Crankbrothers' approach to BOA, implementing a velcro strap for the top closure that will keep everything together in the event of a BOA explosion. I have never had a BOA failure but it's not out of the question.

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I really appreciate the convenience of BOA closures while gearing up for a ride and gearing down afterwards. It's not a big thing but it removes a little bit of friction from the procedure. There is no redundancy built in if you have a double-BOA failure however.


It almost seems like there is something magical going on in the grip department. Generally shoes that are very grippy are difficult to reposition. While these aren't the stickiest shoes I've worn, which I'm happy about, I rarely find my feet slipping unexpectedly. At the same time, repositioning is generally so easy it involves little brain power or anxiety. An element I find a little confounding is that I have a much easier time finding my very particular pedal sweet spot on either side with these shoes. It's almost like I'm riding clipless because I simply put my feet on and I rarely miss the target. Is it the lug pattern? The rubber compound? I honestly can't say but it's a benefit I am down with.

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It seems to me the only reason to have lugs, or any contour at all on a flat pedal shoe, is for grip off the bike. These aren't noticeable on the pedal at all however and the walking I have done has been uneventful, even in the wet.

The only other shoes I've worn with this paradoxical balance of ample grip and repositioning ease are the Northwave Multi-Cross GTX winter shoes, which are entirely different; they are much stiffer and they have a Vibram outsole that doesn't seem gummy to the touch at all. And yet my results were very similar. I haven't yet figured out how to explain this but I will continue to try.

fox union boa flat outsole

After around 20 rides there are only few small pedal scars, so few I'd say that durability should be very good. Photo - Cam McRae

I have worn these with true flat pedals only but I'm confident they will work just as well on convex platforms, particularly for riders who slide their foot forward while descending. I'm generally more focussed on descending grip but these also do well on technical climbs, when my arch is above the pedal spindle. There is some rocker toward the toes but not enough to impact grip in that position, at least not on either Yoshimura or Crankbrothers Stamp 7 (small) pedals.

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The one-piece upper means there are no seams to fail. Protection is good, particularly at the heel.

Upper, Midsole and Protection

The entire upper is one piece so there are no seams to fail. There is venting in the toe, and just in front of the ankle on either side. The heel cap feels sturdy and protective as does the vertical element of the toe cap. Toe protection from above is less robust and the foam in the tongue also feels less sturdy than it could. A gusset supports the lower half of the tongue on both sides, preventing rotation and keeping debris out. I've worn these on some reasonably wet days and my feet have stayed remarkably dry. Construction quality and finish both are excellent.

Stiffness is moderate with good support through the middle, thanks to a reinforced nylon shank, with more flex at the toe and heel for walking comfort. I suspect this stiffness contributes to the excellent grip based on my recent experiences with stiffer flat shoes.

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Grip is undiminished on wet days.


Like most of the shoes I have tested lately, these do not have Fiveten levels of grip. If you want shoes you can only reposition when you sit down on your saddle and completely lift your foot off the pins, you aren't going to be happy here. If you'd rather balance grip while being able to scootch your foot around while standing and descending, these are some of the best I have ridden. It wasn't long ago that it was Specialized 2FO or bust for me but lately I've ridden great shoes from Northwave and Crankbrothers that tick all the boxes. These are right up there with the best I've worn and I couldn't be much happier in them.

The bloom on the rose diminishes some once we talk price. These go for 225 USD and 285 CAD. That's a lot of cake for flat pedal shoes. Obviously the four BOA Li2 dials - the priciest BOA model - contribute to that lofty tag but I can't recall a more expensive flat pedal shoe for warm weather. Much of the goodness will be independent of the closure system however and the lace up Fox Unions are 150 USD/200 CAD, while the canvas version is 120 USD/150 CAD. I can't tell you if these shoes will be worth that much money to you, but these are some of the best flat pedal shoes I've worn.

Fox Union BOA Flat Shoes

Tags: Union Boa, Fox, BOA
Posted in: Apparel - Shoes, Gear, Features

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+3 The Chez Niels van Kampenhout Skooks

I might be odd man out on this, but BOA feels odd to me.  There is a smooth tightening that I just do not like.  With regular lace up shoes I can adjust each lace to fine tune fit.  BOA feels like a consistent squeeze across the whole foot.  Having 2 might help, but for me what I really want is laces with a velcro strap at the top.  Shimano used to make shoes like this and they were perfect for my feet.


It may depend on which shoes you tried on - BOA is applied differently on different designs. Same with laces. Not to discount your opinion, they're obviously different and everyone has their preferences.


+3 Allen Lloyd Niels van Kampenhout dolface

"Shimano used to make shoes like this and they were perfect for my feet."

Well, I have good news for you, I just got a pair of Shimano shoes _just like that _for review.

Ironically I'm a big BOA fan, though.


+3 Jotegir Skooks Cam McRae

It's too bad these don't come in sizes that fit smaller feet. They seem worth trying, but the price is high for a "try" and "trying" a size up isn't always worthwhile. Unlike you I have seen a Boa explosion and replacing them is never simple. I love the idea of a backup strap, even though it may mess up the clean look of these (I do not care about looks. I wear 5.10 impacts which look like clown shoes). I'm still on the hunt for anything to replace my 5.10s. They make a shoe that goes down at a 36 in size, which is closer to my actual size. Ironic that the only size sold out on the Fox website is the smallest size they offer, and I'd bet they're losing customers by not having something smaller than a 37 too. Once again I'll die on the MAKE PRODUCT FOR SMALLER PEOPLE hill.


+2 Lacy Kemp Cam McRae

I sold a lot of BOA stuff in both summer and winter and for better or worse was the first point of contact for all the customers who purchased the BOA stuff, so I too have seen a number of BOA explosions and other failures. Agreed that the stuff is never simple.

On the bright side, any shop can (could?) send away to BOA to get a free boa warranty replacement kit of small parts. We had a few for both summer and winter and could repair 95% of BOA issues on the spot. BOA is also pretty good about just sending bits to people, but honestly, if you're ever considering buying BOA stuff make sure that the shop you're getting stuff from has a BOA kit because it can be the difference between not running your shoes for a few weeks or months and getting them back that day. 

I feel you on the shoe sizing. For both MTB and real life I've always struggled with having to pay for shoes that might not fit in a hope they'll work out sight unseen. For flats I can wear 5.10s with custom insoles (even though a bike park day will bruise my toe a bit, they are a slightly small), but for clipless the only shoe I've been able to find that works OK is from Shimano and they no longer bring them into north America above size 48 (I am a 51 EEEE in euro land), and to add insult to injury, they don't let any of the European shops ship the available euro sizes to NA (come on guys). I have been limping along a pair of Shimano MO88s for about 5 years, at this point they're more Shoe Goo than original rubber. 

So while MAKE PRODUCT FOR SMALLER PEOPLE doesn't apply to me, I am with you in solidarity!

In my case 5.10s actually are clown shoes.


+3 Niels van Kampenhout Hbar Cam McRae

Anyone can request a free replacement BOA from BOA. Just provide shoe model and photo of receipt to the form on the website and they post it to you for free.

It's the first thing I do when I get a new pair of BOA shoes. The Li2 BOA are the business though with the precise micro adjust in both directions.

On the Union Boa, I have the clip version (but they are the same build other than the sole) and I don't know about the physiology of the test riders ankles but the anchor/ inner/ medial loop for the upper BOA 'string' is just a smidge too high and causes a pinch on the inner ankle joint. This is a common comment amongst the local Fox Union BOA wearers! 

They are also pretty generous on the heel pocket ie loose, although it could be that I have skinny heels, which combined with the upper inner loop anchor position creates a strong pinching sensation when hike-a-biking. 

Hike-a-biking is something that I do not think a lot of product development teams consider even for an "enduro" shoe which seems like a bit of an oversight to me.

+3 Jotegir Skooks Cam McRae


I did the free Boa replacement through their website and can confirm it works as advertised. But overall I find Boa an unnecessarily complex solution for a problem that is solved quite simply and elegantly by laces and velcro.


+2 Niels van Kampenhout Cam McRae

Couldn't agree more regarding BOA on MTB shoes Niels. It's an added complexity that is simply not needed. Free replacements do me no good when my BOAs blow out on the top of a mountain.  My motto is to use the simplest technology that will do the job, and laces are impossible to beat on that score.



I tend to agree. BOA seems nice for snowboard boots and helmets. but it seems like overkill for MTB shoes. That being said, I've not owned a pair, but my partner tends to run dancing shoes on his MTB so all of his are BOA equipped, and more than one has exploded.


+5 BarryW Deniz Merdano Cam McRae Morgan Heater Lacy Kemp

Sure, its easy to make fun of him online for his choice of MTB footwear but when he shows up to take you out for a night on the town you'll be thankful he came prepared to cut a rug.

+3 Andy Eunson BarryW Cam McRae

I don't get it. How do the cleats attach?


+2 Skooks Cam McRae

BOAs are showing up on everything from ski boots to bike shoes, so what happens if they screw up tomorrow/ next year/ 10 yrs from now is my take ? I can still get shoe laces for my 661's even tho that company is long gone SO  I just give BOA's a pass.

I got small feet so I would never see 5:10's in my size, it eventualy took the LBS 6 months to get them and they work so thats my shoe now


+1 Skooks

I’ve had a few Boa shoes both road and mountain. I find most of the time it’s easy to overthighten the Boa. But easy enough to loosen, even with the cheaper one way Boa. Ratchet straps work well for me though. Laces are fine too until you get home with wet stuck laces on muddy shoes and a full bladder.

I’ve never thought the tread pattern on a flat shoe provided pedal grip. It’s only for walking. Some people do though. There was a 5:10 with a smooth under the ball pattern. Was that any less grippy? Or was it easier to move the foot to find a good spot?


Tread patterns help interface with pedal pins. Those flat-soled Five Tens didn't last very long and even then I think the idea was that it was super soft and sticky rubber, meant to act like a blank slate so that your pins would stick well wherever they contacted it.

+1 Andy Eunson

I used to think that before I tried the Northwave Multi Cross GTX. The have no lugs at all. Only thin slices in a solid sole. And the grip is amazing. I am sticking with my aforementioned thesis. 



Try moving a flat pedal shoe on a pedal by hand, the pins catch in the slots or tread or whatever your shoe has so if the shoe has your weight on it there is definatly extra traction compared to a pedal with no pins


Interesting. It seems to me that test assumes your alignment with the pins is at least in part off the lugs so that motion would have the pins contact the edge of a lug, slowing it/stopping any slip. Otherwise the friction should be similar or even a little less. 

This must be tricky for shoe designers to navigate because of different shoe sizes. I wonder what it would be like if all of your pins lined up between the lugs on your shoe? The height of pins would come into play here as well.



well its really easy to test it ^^ out in your own garage. 

Also I only have pins in one side of my pedals so I know right away which side of the pedal i'm on cuz no pins =no grip, I started taking pins out of one side cuz I would thrash all the  pins on both sides of a pedal in  1/2 a season and end up with no traction, but with pins on only 1 side i flip them up and they don't get trashed , yeah its a wierd idea



Anyone local stocking these to try on?

+1 Konrad

I know Norco North Shore stocks Fox shoes but I'm not sure they have these in stock. On their website they only list the lace up version but they will work for the try on.



These seem great. Nice seeing more premium flat pedal shoes.

+1 finbarr

I agree. Flat shoes - and pedals actually - used to a neglected backwater in the market, with the exception of fiveten. For years everyone else was trying in vain to catch up and finally there are several really good options.

I have been surprise and very impressed by these, and the new Crankbrothers Trail shoes.


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