Fox Union BOA shoes review

After a lengthy design process, Fox Racing unleashed its shoe range to the public earlier in 2023.

Of the three models available (two designed to work with clipless pedals, one for flats), the Union BOA sits at the top of the pile, both in terms of claimed performance and price.

The solid fit, impressive comfort and customisability make the Union BOAs well worth a look for those with deep pockets looking for a mountain bike shoe that’ll work well on the trail.

They’re more versatile than their downhill and enduro DNA might suggest. But are they really worth the high asking price?

Fox Union BOA shoes specifications and details

What really sets the Union BOA shoe apart from the regular Union shoe, which uses a lace and strap closure, is the presence of the two Boa Li2 dials to secure the shoes to your feet. Otherwise, they share just about everything else.

The malleable one-piece, weather-resistant upper features a reinforced, moulded toe cap to help protect against rock strikes and accidental whacks into the floor, while the stiffened heel section is said to help lock your feet in place to prevent any kind of lift as you pedal or walk.

There’s padding featured throughout the tongue and around the ankle cuff, though it’s fairly minimal and certainly firmer than the Union BOA's closest competition.

Perforations over the top of the toe box and in small sections either side of the foot are there to help aid breathability.

Fox offers two different, easy to swap arch support inserts that attach via Velcro to the underside of the insole. Both the side-specific ‘high’ and ‘low’ inserts are included in the box and should help to tailor the fit.

To help improve power transfer, a reinforced nylon shank has been used.

Underneath, the all-important outsole is made from Fox’s Ultratac rubber, which features evenly spaced, fairly low tread blocks, all of which are of about the same depth (the toe and heel treads aren’t any deeper, as found on other shoes to improve traction when walking).

A long cleat pocket with decent-length slots helps to ensure there’s sufficient clearance (including either side) and space to get cleats positioned just where you need them.

Fox has included ‘Power’ and ‘Control’ markings within the cleat pocket too, suggesting that placing your cleat further forwards towards your toes will improve power. Shifting it further towards the mid-foot will boost control.

I won't bore you with all the ins and outs on this subject, but I’d say don’t be swayed by these markings and simply set the cleats where you feel they’re most comfortable.

My UK8/EU42 size shoes, with Crankbrothers cleats fitted, weigh 902g, which is decently light for tough mountain bike shoes aimed at downhill and enduro.

Fox Union BOA shoes setup

I tested the Union BOA shoes with Crankbrothers Mallet DH and Mallet E pedals. Both pedals have a broad platform that surrounds the clip-in mechanism and feature pins to boost traction.

As I tend to do with every pair of shoes I use, I shunted the cleats as far back in the cleat slots as I could (with a single plastic spacer beneath them). I canted the cleats slightly so the top pointed towards my big toes, with both cleats sitting close to central over the slots.

Fox Union BOA shoes performance

Fit and feel

Getting the Union BOA shoes on is extremely easy, thanks to both Boa dials popping up and open, releasing any tension in the cord and providing loads of room to slip your foot in.

You can instantly feel the shoe cup your heel, while there’s ample room through the mid-foot, with the toe box feeling broad and spacious, allowing your toes to spread out comfortably.

Being able to alter the arch support (using the differing inserts that attach with Velcro to the insole) is a nice touch. Having tried both the high and low options, I ended up removing the inserts completely, leaving the footbed feeling flatter and more neutral – similar to shoes such as the Crankbrothers Mallet BOAs and Specialized’s 2FO ClipLites.

Tightening the Boa dials creates a very nice, even tension across the top of the foot that feels very secure.

Although the padding isn’t particularly thick or massively plush, it’s in the right places, ensuring the Union BOAs are decently comfortable.

Overall, the fit feels impressive, solid and protective. That’s thanks to the tough toe bumper, but also the relatively tall, supportive fit around the ankle.

On the bike

Because the cleat pocket is quite deep (and the Crankbrothers cleats quite shallow, even with a spacer beneath them), clipping in wasn’t as distinct as it can be with other shoes. That’s down mainly to the sole that surrounds the cleat pocket contacting the pedal platform.

Winding in the traction pins on the pedal platform helped alleviate this and made clipping in and out a more marked affair, removing any vagueness I’d felt previously.

The feel through the shoe isn’t as pronounced as others. That meant it took me a little more time to feel perfectly at home clipping back in through the exit of a turn, in the heat of the moment.

This is down largely to the reasonably stiff feel through the shoes. I found I got used to this quickly – it’s something that’s harder to get accustomed to if the cleats won’t go as far back. In this case, Fox’s cleat slots offer a decent range of adjustment.

While the cleats might not sit quite as far back towards the mid-foot as some, the difference is only a few millimetres, so it’s nothing to worry about.

That stiffness makes for a shoe that feels efficient and direct as soon as you put the power down, though. Stamp on the pedals and there’s very little flex through the shoe.

Naturally, using clipless pedals with a platform will offer more support and can mask some flex, but riding the Union BOAs back-to-back with other, similar shoes highlighted their stiffness further.

I quickly grew fond of the Union BOAs and when swapping between shoes, missed their well-supported, protective feel. The lack of feedback through the sole is something you get used to, and I found it to be a bonus when riding rougher trails.

One downside to that stiff sole is I found the Union BOAs less comfortable to walk in than some, especially when pushing the bike up really steep pitches. Here, despite the well-shaped heel, I found it still slipped uncomfortably on my feet.

Overall, this isn’t a massive issue unless you’re considering using these for lengthy hike-a-bike sections of trail.

The other benefit of the stiffer feel through the sole is the Union BOAs will work more effectively for trail riding, rather than just downhill or enduro duties.

How do the Fox Union BOA shoes compare?

I rode the Union BOAs back-to-back with the Crankbrothers Mallet BOA and Specialized 2FO ClipLite shoes.

Both the Mallet BOAs and 2FO ClipLites offer more flex through the sole than the Union BOAs, and, as result, don’t feel quite as effective at transferring power to the pedals.

However, that flex does equate to more feel through the shoe, giving you more accurate feedback as to where the pedal is beneath your foot. It also means that when walking up steeper hillsides, the Crankbrothers and Specialized shoes are a little more forgiving.

The 2FO ClipLites have a similar amount of padding to the Union BOAs, though the Mallet BOAs offer softer padding that’s more plentiful. This results in a more comfortable overall feel than both of the other shoes.

Neither the Crankbrothers or Specialized shoes feel as sturdy or as protective as the Fox, though.

It’s a close call across the board, and while the Union BOAs feel the most solid, stiff and efficient, the Mallet BOAs take the prize when it comes to overall comfort, just ahead of the Specialized 2FO ClipLites.

Fox Union BOA shoes bottom line

The Union BOA shoes from Fox offer an impressive, customisable fit, a very solid feel underfoot and enough stiffness through the sole to make for efficient pedalling without muting pedal feel too much.

They’re not as comfy as some, though, especially when walking up steep hills pushing the bike, and they’re certainly not cheap.

But the tough build, plentiful amounts of cleat adjustment and stiff sole make for a shoe that works well on the bike.