Stan's NoTube Flow MK4 Wheel Review


by Dario DiGiulio

When reviewing a product like Stan’s Flow MK4 wheels, it’s important to remember that the modern mountain bike is a complicated contraption. It is the sum of many parts designed for various types of off-road fun. When it comes time to upgrade things, it’s far too easy to get lost in the sea of components and neglect the parts that really make a difference. Amongst those critical upgrades are the wheels you roll on, which can have a drastic effect on the way your bike rides. Stan’s No Tubes has a long history tuning the performance of rims to better suit the needs of mountain bikers, but at times their full wheel builds have fallen short due to shoddy components. As their newest offering in the aggressive wheel market, do the Stan’s Flow MK4 wheels stand up to the demands of modern riding, and will they serve as a significant upgrade to your bike? We put a set through the wringer so we could determine if that is the case.


Stan’s is one of those companies that has long done things their own way, so when they make a change to their lineup, it’s worth a second glance. New to their 4th generation of rims is an asymmetric rim profile, something we’ve been seeing a lot from more brands these days. The idea here is to better balance spoke tension between both sides of the wheel, which should make for a longer lasting and better performing build. The rims still use Stan’s hookless bead technology, which makes for a very easy and secure tubeless setup, at noticeably lower pressures than a lot of other rim designs out there. The folks at Stan’s No Tubes have settled on a 30mm internal width, which is more or less the settled standard for the 2.4-2.6″ tires most of us are running these days.

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One area of exciting improvement with the new Flows are the completely redesigned M-pulse hubs, now made in partnership with Project321. P321’s boutique offerings have been a feature of baller aftermarket builds for some time, so it’s quite impressive to see them offered on a more cost-focused wheelset without too much fanfare. These hubs implement a unique drive system that uses magnetic pawls as opposed to the traditional push-spring system, which Stan’s claims will reduce freewheel friction and make for a more consistent and reliable engagement over the life of the hub. Speaking of engagement, these wheels should satisfy anybody who lusts after a crisp buzzy sound, as their 216 points of engagement (just 1.66°) leaves little room for pedal slop.

On the nitty-gritty wheel build side of things, they’ve stuck to the traditional 32 hole 3-cross pattern, with double-butted Sapim spokes and alloy nipples. While not as long-lasting as their brass counterparts, using alloy does reduce quite a bit of the rotating weight in a wheel, so it’s an understandable choice. The complete wheelsets come in two size options: 27.5” or 29”, and the respective weights are 1792 and 1882 grams, respectively. Stan’s does offer the rims on their own if you want to go the custom route, at $129, or the full wheelset can be purchased for roughly $310 up front and $655 out back.

Stan's NoTube Flow MK4 Wheel Review


I’ve spent my spring hammering a set of 29” Stan’s MK4 Flow wheels in conditions ranging from sloppy wet PNW loam to bone dry rocky California trails, and they’ve held up to all the abuse quite well. I tend to run carbon rims on my personal bike, not for the weight but for the durability that heavier layups can offer, when it comes to how frequently you have to true and tighten your wheels. That being said, this alloy wheelset has impressed me so much I’m not rushing to get back on my personal wheels anytime soon. A big part of that comes down to ride feel, and the muted predictable character these wheels have. In contrast to some high-tension ultra-stiff carbon wheels I’ve tested in the past, the Flow MK4 wheels track super nicely when things get rough, and still corner well enough to hold their own and maintain my confidence. Upon receiving the wheels, I noticed the lower build tension that Stan’s seems to use, a choice that I’m a big fan of. While this might mean the wheel is slightly less torsionally stiff, it makes for a forgiving feel that doesn’t ping you off-line when carving in rough terrain and seems to hold up a little longer before it comes time for truing and tensioning.

I’m a big fan of the 30mm internal that most brands have settled on, as it makes for a nicely rounded tire profile for predictable grip and good steering characteristics with my typical 2.4”-2.5” rubber. When it comes to putting those tires on, I’ve had no problems with mounting a wide variety of tubeless options up to these rims, all with my no-name floor pump. Things snap into place at a relatively low pressure too, which should be reassuring to anyone who’s had a tire explode off the rim at 50psi.

Stan's NoTube Flow MK4 Wheel Review

Durability has been impressive so far, and not for a lack of abuse. I spent a week riding these wheels in San Luis Obispo, CA, which is notorious for the massively chunky rock gardens that litter the high-speed trails. Even after some pretty significant tire bottom-outs, the rims are dent-free and remain easy to true – a quick job that should be expected on any new wheelset, as tension always takes a few miles to settle in. I almost always run inserts in my tires, but I’ve chosen options made for ride feel more than for rim protection, namely Rimpact up front, and Tannus in the rear. These definitely play a role in keeping the alloy rims dent-free, but even with some foam in there you can manage to flat spot a rim in no time in the rocky chunk. I had one particularly heinous jump case this past week, and the rear wheel rolled away just fine, with only the slightest wobble that was easy to true when I got home.

At the heart of these wheels, I’ve been really impressed by the new M-pulse hubs Stan’s and Project321 developed. In years past, house-brand Stan’s hubs have left a lot of room for improvement, but these are a part I could see people hunting down on the aftermarket for their custom builds. They have a lot of carefully considered features that makes them stand out from the standard offerings most brands lace into their wheels. Complex and effective weather seals keep the internals clean and functional, adjustable preload collars that allow you tune the rolling speed and adjust for any frame differences, and double row freehub bearings should last a whole lot longer than more minimal designs. Plus, they sound nice – kind of Chris King-y at first, but as things wore in, they got a little louder and more crisp.

After shrugging off a barrage of abuse through the test period, the Stans Flow MK4 wheelset finally met its match at the end. Holding it wide open on a fast trail, a large g-out in a hole proved to be too much for the integrity of the wheel, leaving it with a significant flat spot. It was round enough to roll out back to the car park but required a new rim to return it to a wheel I’d be confident in pushing hard again. This may have been a freak accident given the durability of the wheel throughout the rest of the test, but the impact wasn’t anything out of the ordinary, so it has left me scratching my head.

Editors Note: We got in touch with Stans for some feedback on the incident, with a particular interest in the spoke tensions used in their wheel build, which were lower than we’ve come to expect from a pre-built wheelset. Here’s what Gunnar Bergey, Marketing Director for Stans, had to say:

Flow MK4s are built to 105 KgF with a max recommended spoke tension of 125 KgF. 105 KgF is definitely a bit lower than what you’ll see on manufacturers wheels out of the box. The process in which our wheels are built results in less tension drop during the “breaking in” period after about the first month of riding. That allows us to build the wheels at a lower tension and eventually ship them knowing they won’t drop after the “breaking in” period.

We don’t recommend that heavier/more aggressive riders add spoke tension to increase the lifespan of their wheels. We’ve found that regardless of spoke tension, a major square edged impact will compress the entire wheel and the end result is still damage to the rim. The increased tension does however reduce the ride quality and won’t allow our rims to deflect as intended.
Stan's NoTubes MK4 Wheelset Review

The Wolf’s Last Word

The seemingly endless upgrade opportunities on a mountain bike can be pretty overwhelming, but I think a high-quality wheelset is one of the most substantial changes you can make to a stock build. People tend to immediately look to carbon when shopping for aftermarket wheels, but a high-quality alloy wheelset can offer equally impressive performance gains over OEM options. With a fantastic ride feel and some very nice finishing touches, the Flow MK4 wheelset should be a strong contender for those looking for something new to roll on. At around $965 for the wheelset, the Flows are pretty competitive with other premium alloy wheels, and well under half the price of most carbon options on the market. Stan’s Flow MK4 wheels survived a huge amount of abuse through the testing period, and only faltered after one freak impact at the very end. I’d still stand by the wheels as being a solid option for the gravity crowd, as any part can break in the right (or wrong) circumstances, but they’re not totally indestructible.

Price: $308 (Front) / $657 (Rear)
Weight: 1882g (pair, claimed)

Disclosure: Our team selects all of the products we review and do so with honesty and objectivity in mind. Some of the products we receive come directly from Competitive Cyclist, who also value our readers and have offered them a 15% discount (exclusions apply) on their first purchase by using LOAMWOLF15. Through this program we may also receive a small commission at no cost to you. Thanks for your support, TLW.

We Dig

Comfortable, forgiving ride feel
High quality hubs
Good overall durability

We Don’t

Alloy nipples aren’t most robust
Not the most budget-friendly alloy wheels
Not Indestructible


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