• Clever Training

First Look: The 4iiii Fliiiight Smart Trainer


Remember back in May when 4iiii announced the acquisition of STAC the company (which made trainers and aero/fit stuff)? And remember when they hinted that they’d have a new trainer product in time to show at Eurobike?

No? Ok, well, I did. And more importantly – so did 4iiii and STAC. And true to their word they’ve got a new trainer product to show at Eurobike, the Fliiiight trainer. Yes, again, there’s four i’s in there. My keyboard already hates me enough after the last 24 hours.

Now if you put on that memory hat again you might remember that STAC’s past trainers have been unique in that the resistance is done via magnets that don’t actually touch your rear wheel, but rather generate forces to resist it. As such, there’s zero sound from the trainer itself, with the only sound coming from your normal bike drive chain (which in this case mostly depends on how clean you keep it).  Their concept carries through to Fliiiight, except now with a far easier setup/configuration, and no more need for wheel weights.

Here’s the quick overview video:

Got all that? Let’s dive into the tech specs of the updated version.

Tech Specs & Initial Ride:

The best way to sum up the entire 4iiii Fliiiight is in three words: Not complicated anymore.

Alternatively: Not convoluted anymore

Further: Not fugly anymore

I’ve gotta believe that when 4iiii/STAC sat down to build this iteration, they looked at their top complaints by users and reviewers and simply checked through them all. The previous version was complicated and convoluted to set up. Not hard, but just prone to plenty of places it could go wrong. And when it went wrong – then people had a bad setup. I remember the first time I tried it out on their unit at the show floor and was like ‘Woah, this is so much better than my setup at home!’, after which we talked through the nuances of that setup process for their unit versus what I did wrong. Once I went home I was able to replicate it.

So to start, the entire system now has this crazy robotic automatic calibration ‘thing’. Seriously, the entire back half of the trainer has an internal motorized slider that moves left and right independently (the two arms), and then figures out where your wheel is (independently) and shifts in real-time to match your wheel and the sub-second variations of your accelerations (For real: Just watch the video).


But it gets more fascinating than that. They’re using an optical sensor affixed to the tips of the little poles near your rear wheel to measure acceleration so that they can adjust for it in real-time on resistance.


All you do is place this small white straw/sleeve bit on your spoke, and it uses that as the reflector:


Next, if you actually watch the system in the back, it ‘pulses’ in and out dependent on your cadence. One of the things 4iiii says this addresses is the sub-second changes that you output on the wheel-speed, which in turn means the entire thing feels smoother since the system can compensate on it constantly and instantly. But how does it feel? More on that in a second, first, some tech specs.

So let’s run through the key tech specs:

– Price: $599USD, October availability
– Wheel-on trainer, requires metal wheel (not carbon rim)
– Portability: Yes, with 2hr built-in battery if you want
– Max Resistance: 2,200w
– Max Incline Simulation: 7%
– Accuracy level: +/- 1%
– Trainer Control: ANT+ FE-C & Bluetooth Smart FTMS
– Power Transmission: Both ANT+ & Bluetooth Smart open power signals
– Cadence Transmission: Yes
– No more wheel weights needed

So why aren’t wheel weights needed? Well, previously the wheel weights served to increase the flywheel weight which in turn increased road-like feel. It was also to negate the lack of precision on the magnetic resistance aspect constantly changing. In other words, it provided smoothing. But with the fast resistance changes, they can do it all magnetically.

Actually, before we talk about ride feel – it’s actually a portable trainer that’s viable for warm-ups at races. That’s because it has a battery built into it, which gives you about 2 hours of ride time if needed:


And, in a signal to the rest of the industry to ‘catch-up’, they went with power via USB-C. In fact, it goes one step further, it’s got a trip-friendly detachable magnetic USB-C cable included with it. Kinda like the old MacBook chargers (you can also buy this cable for your newer MacBook or USB-C device). So if you trip over it, the cable part simply detaches and nothing is broken:

DSC_6432 DSC_6435

Now back in the STAC/STAC Halcyon days this trainer was more well-suited towards ERG, given its slightly lower incline resistance, and slightly less road-like feel. In some ways, that stays the same. The unit tops out at 7%, which is lower than most trainers of this price point. At the same time, my guess is that you’ve never bothered to change your Zwift ‘Difficulty Level’ setting from the default of 50% (on purpose or otherwise). So that means that any 14% grades in Zwift actually become 7% grades from a trainer feel/resistance standpoint. And again, almost nobody (except apparently me) changes it.

So since there are almost no grades above 14% in Zwift, then the 7% limitation of this trainer probably doesn’t matter too much in practice for most people (unless you like climbing up simulated hills with full resistance, in which case this isn’t the trainer for you).

That takes us to the next bit: Road-like feel of the Fliiiight.

It’s kinda-ok. It’s not bad, but it’s not fantastic, and the other units at $599 have better feel. Still, I’ll defer judgment till the final software/hardware version. There’s some software tweaks they want to make – which can and likely will impact road-like feel, since everything about this trainer is driven by the software and how efficiently and correctly it can move the magnets (including positioning).

Right now 4iiii says that the final version of hardware should be wrapped up in the next couple of weeks at most, and then they should be ready to start shipping in October.

Of course – as with the Fliiiight, the main appeal of the trainer is simply the silence, as well as lack of vibrations. There are none of either. So the only sound you’ll hear is that of your drive chain, and for apartment dwellers that may have thin floors or walls – there’s no vibrations from the trainer, since your rear wheel is just floating spinning in air, not physically rubbing/driving against anything like a typical wheel-on trainer or direct drive trainer would. Or perhaps, folks looking for a light and portable solution to take to races that can still throw down some serious power in a structured workout.



I’m happy to see 4iiii/STAC listened to all the feedback about their previous generation units, perhaps most notably starting with the looks of it. Gone is construction cone orange, and in comes a sleek black unit. Sure, it’s not as flashy, but it’ll more easily blend into people’s apartments and living rooms without folks avoiding that portion of the room like a public works project.

On the technology side, the new robotic alignment system is simply cool to watch. I mean, sure, it’s more accurate and all that jazz…but let’s be honest: Everyone is entertained by crazy robots. Still, it does serve a purpose: Accurately configuring your wheel for each use, and then being able to track your wheel in real-time as it rotates. All of that means that gone are the days of finagling with the sensor (hopefully). And getting rid of the wheel weight fiasco is also much appreciated too – it means you can use your bike wheel more easily inside and out (versus before you mostly just left a secondary wheel with the weights on it).

Of course, the downside to the trainer is that the road-like feel isn’t super high-end at this point. There’s also the limitation of needing some form of metal rim on your wheels. If you’ve got fancy carbon race wheels, those won’t work. Though given virtually every bike you buy comes with a set of basic metal-rimmed wheels, I suspect most athletes have a set somewhere around.

Ultimately, I’m looking forward to testing out the final version of this, hopefully later this month. I’ll circle back then or early October with a full in-depth review once that happens.

With that – thanks for reading!

Heads up: You can pre-order the 4iiii Fliiiight via Clever Training. Doing so helps support the site here, and you can use DCR Reader Coupon Code DCR10BTF to save yourself 10%, plus of course free US shipping. Thanks for the support!

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  1. Jon S

    This looks really interesting, and good to see they’ve listened and acted (quite significantly) on all the feedback.

    BTW is this a typo in your ‘key tech specs’ list?
    “Wheel-on trainer, requires metal wheel (not carbon frame)” – suggest ‘frame’ should read ‘rim’

  2. Stevan K.

    Interesting and nice to see that this “so simple that it is genius” technology survives. Kudos to 4iiii for seeing the potential and picking up Stac.
    Typo?: “– Wheel-on trainer, requires metal wheel (not carbon frame)” Should read “carbon rim” ?

  3. Chris Benten

    This is pretty cool…now I need to replace my rear hub…a DT Swiss unit that sounds like a string of firecrackers shooting off.

    On another note, are you doing a preliminary look at the TrueKinetix bike? I would like to know more about the 20% power loss on a trainer.

  4. Graham R

    What are the chances they will have some sort of an upgrade kit for existing customers I wonder. I went from basic, to power, and almost pulled the trigger on the halcyon before they got bought out.

    STAC customer service has always been amazing to deal with.

    • Rob F

      As an owner of the power meter version of the STAC, I’d also like to see this option.

      Anyone from 4iiii reading these comments, it sounds like several of us would be interested. I happen to like the obnoxious orange.

    • Matthew Weigel

      It looks like it still mounts the same, so they COULD sell an upgrade kit… but 75% of the pain I had upgrading my basic STAC to the Halcyon was in futzing with mounting it correctly. I think there’s a trade off they have to manage between rewarding an early adopter with the latest and greatest with lower prices, vs. punishing an early adopter with having to install the resistance unit again.

      My advice to you: the power unit is a sweet spot. Not too complicated, very functional.

      My advice to 4iiii: offer an upgrade price to early adopters but just trade out the Fliiiight for the earlier STAC unit – don’t make people deal with swapping resistance units.

    • Hi Graham,

      Yes, you will be able to retrofit your old trainer with our new resistance unit. This will become available after the product starts showing up in stores in October. Stay tuned for more details!

      Scott Cooper
      Product Manager, 4iiii Innovations

    • Hello Scott,

      As an early owner of first the STAC, followed by the Halcyon upgrade kit, I would rather have a swap with a full Fliiiight trainer than fidling again with an upgrade kit. Would also look much cooler than an orange STAC frame with a black resistance unit.



    • Steve

      Thanks. The upgrade from a Halcyon would interest me. Could you use the wheel weights with the new resistance unit? What would that do for road feel?

    • Hi Ringo and Steve,

      Ringo, for now we will just be offering the upgrade kit consisting of a resistance unit but appreciate your feedback. It’s awesome to see that you’ve stayed with the trainer along its entire development path!

      Steve, you could use the wheel weights but the Virtual Inertia that is now included in the firmware makes up for the wheel weights not being there. You should be getting a smooth riding experience without the hassle of the weights.

      Thanks for the questions and feedback!

      Scott Cooper
      Product Manager, 4iiii Innovations

    • Joel

      Looking forward for upgrade news! It seems that upgrading to the new resistance unit should be less of a hassle than before.

      Any idea on price range, or if it will be a trade-in program (for resistance unit – I for one, like the orange trainer)?

    • Andrew Edge

      There will be an upgrade kit for current owners. The user will simply remove the old unit from the frame and bolt the new one in place. Should be out after the initial orders for the fliiiight are filled.

    • One small correction hear, the current FW might get confused with wheel weights in for the optical sensor so we actually would not recommend trying the Fliiiight with wheel weights. Sorry for the misinformation!

      Scott Cooper
      Product Manager, 4iiii Innovations

    • +4 to STAC & 4iiii for offering a resistance unit upgrade for existing customers — AND for designing a good modular system that allows for upgrades like this. I’m looking forward to riding on it.

    • Tom

      Hi Scott,
      Any way that we can get on a mailing list to hear about the future upgrade?

    • Lance Classen

      Hi Scott,
      Does 4iiii have any update on the release date?

    • Graham R

      Scott, Thanks for the info! Like the others, any way you can get an update about the upgrade kit?

  5. Ed B.

    Do they have a solution for the trainer if you want to keep a rear disc wheel on the bike?

  6. Miranda

    I’m a very satisfied Stac Halcyon user (and I second the comments about great customer service!) so I’m excited to see things moving forward under the 4iii’s umbrella. I won’t be upgrading because the traffic-cone aesthetic works in my unfinished basement and I already have a trainer-wheel with weights that I swap out. But this looks like a great option for new customers.

  7. Kiara

    Awesome update!! I have the first generation STAC trainer, which they upgraded with newer parts twice for me in the first couple years. These were really hardworking and passionate guys and I am happy to see their ideas grow so large.

  8. Andras

    Helli Ray, i am a bit confused this metal definition. Will it work with Al alloys? I always thought that magnets will not work on Al materials but on steels only.

    • JD

      The rim cannot have any steel in it. A non-ferrous wheel (aluminum) is what you need.
      The STAC Zero support site is still operating. FAQs are answered here:
      link to stacperformance.zendesk.com

    • Paul S.

      Any metal. Anything that conducts electricity well. This does not work by “attraction”, but by inducing a current in the rim to produce heat. The rim is actually warmer than room temperature after a ride (although not excessively so).

      In fact, you’re much better off if there’s no steel anywhere. I had the original Kickstarter STAC (upgraded afterwards to a Halcyon), and I had to use zip ties to keep the magnets from being attracted to the rim. I couldn’t figure out why (I knew the rims weren’t steel because I could test them with smaller magnets) until I finally realized I was using wire beaded tires, and the wire was steel. Switching to Kevlar beaded tires fixed that problem. I’m sure that the actuators in this are probably strong enough that wire beads would work, but it’s better not to have any steel around at all.

  9. DJH

    I just have to say that it is really cool to watch the progression of STAC, and how their technology and trainers continue to progress. The arms automatically adjusting is really, really cool! I do wonder about the reliability and expected lifespan of those motors. I love seeing them continue to innovate!!

  10. David C

    So… It would work with mountain bikes?

  11. Tizzledk

    You said 599 is a bit much for this trainer what do you think is a better price DC? I am very much interested in the trainer but I too think 599 is a bit steep. That being said, depending on your finalreview I may get it…perfect for Zwift on Apple TV, easy to move and put away (easier than my Direto), so it might be it. My only concern is durability .

    • Nate Park

      Durability is not a problem.
      I’m using STAC Zero(upgraded to Halcyon) about 2 years without a problem.

    • I think this trainer would do super well at $499. There’s nothing wrong with $599, but it’s just a tougher landscape to compete against.

    • Joel

      Just curious, what does $599 trainer has that this one doesn’t. Maybe I’m biased because i have a Stac Zero halcyon, but it seems than the price is competitive with others at the same level.

      Maybe not the same road feel, but you have said to get the best road feel you need to go to over $1000 models. But its is absolutely silent, like nothing else on the market. Even the most expensive units can’t claim this.

      it has better power accuracy (TBD i guess) than others at the same price level ($500-$700). If the claims are true, you would need to go all the way to a trainer 2x the price of this one for the same accuracy.

      And yes, 7% inclination is not the best, but for probably most people it more than adequate (and if im not mistaken the halcyon could potentially do 12%).

      Yes, i would love it to be slightly less expensive (that why i bought to halcyon on sale for 375, and i would buy the new one at $499 right now), but I can’t see why its a tougher sell at this price point (if i didn’t had a trainer already, this one would be at the top of my list).

    • Koen

      I agree with Joel here. No tire wear and completely silent, probably more-than-decent power accuracy. Should blow all wheel-on trainers out of the water. So that makes it compete with direct-drive trainers which start at 799-899 or so. Bu then again, I am no DC Rainmaker…

      Looks like an interesting candidate to replace my Tacx Vortex when it needs replacement

  12. Dude guy

    I’m very curious about the road feel comments. Would adding a bunch of weight to the wheel as in the prior version fix that? Has anyone else compared a stac to a neo or kickr for road feel?

  13. Richard

    Love it! Solves all the issues with wheel on trainers and avoids having to fiddle with a dirty drive train. It’ll be interesting to see a full review.

  14. Steve

    Utterly pointless. Wont sell many of them.

  15. Andreas

    Just moved up on my list as most interesting trainer to get this year. I’m looking for something as quiet as possible for riding in my living room without spending 1300€ on a Tacx Neo 2T.
    On my Kickr Snap, I’ve always preferred doing ERG instead of simulation rides in Zwift. For a large part because the Snap really gets loud/starts to vibrate in higher gears.

    So I really hope that 4iiii will be able to deliver by the end of October via some German retailer.

  16. Ginny

    Does this accept a wide range of wheel sizes?

    The Kurt kinetic trainer I have works nicely with both my 650c bike and my husband’s 700c bike. I’ve even had a 24” kid’s bike on there, but that sounded like a small jet due to the knobby tires.

    • Hi Ginny,

      Yes, we can accommodate a wide range of wheel sizes with no issue switching between 650c and 700c. It’s a simple process of adjusting a couple of set screws. You should also be able to get away with your kid’s bike on there too so the whole family can join in the fun!

      Scott Cooper
      Product Manager, 4iiii Innovations

    • Craig Martin

      Scott – is there any thought to support wheel sizes down to 20″ (406 BSD)? I know it’s a smaller market, but is a very small modification given your mounting. This would be amazing for BMX race bikes, and I know I’ve talked to people looking for 20″ compatibility for recumbents, trikes, and folders as well.

    • Hi Craig,

      Unfortunately we’ve tried riding 20″ wheels and they are too small for the Fliiiight Trainer. We appreciate your interest and we recognize the need for some riders to accommodate these wheel sizes. It will certainly be a consideration for the future for us. Thanks for your question!

      Scott Cooper
      Product Manager, 4iiii Innovations

  17. Rob P

    Regarding use for race warm up, what’s the biggest tire that can fit in there? Looks like it could be interesting for cyclocross warm up without wearing out an expensive tire, but the clearance looks a little tight.

  18. Mario

    Really love the concept of the 4iiii smart trainer(s).
    I currently own a Kickr Snap – which is a good reference since they’re in the same price segment – so here’s what I am taking from this article: Fliiiight is way better in terms of noise emission, and it saves people a lot of time because it allows them to keep their road tyres (also, less wear). But the 7% incline on the Fliiiight is a real dealbraker because I absolutely love hard climbs.
    Hope the people at 4iiii keep up the good work and manage to up that resistance on their next version.

  19. Ben S

    The Clever Training link takes you to a landing page for the Vivoactive/Vivomove.

    Also, once I enter Clever Training’s site from your website and add the 4iiii Fliiiight to my cart does anything else I add to the cart before purchase help support the site?

  20. Chong

    I live in a condo and got a Halcyon after my neighbor started complaining about the noise my Wahoo Snap was making. It has been almost a year and so far no noise complaints.

    One issue I have is that one of the magnets always gets out of whack and rubs the rim resulting in having to constantly adjust the position of the bike. I hope this version eliminate that. Looking forward to seeing what an upgrade kit will be.

    • Hi Chong,

      Yes, there’s new firmware for rim detection so you shouldn’t have this problem anymore. There’s also an easy “recenter” button in the 4iiii App if you run into any trouble. Thanks!

      Scott Cooper
      Product Manager, 4iiii Innovations

  21. Daniel Dionisi

    Its compatible with disc brake wheels (road or MTB bikes)?

    • Chad McNeese

      You will need to swap in a trainer specific thru-axle, but yes, this should work with newer disc equipped bikes. The ones from Saris, Wahoo, Kinetic, Robert Axle Project and such should work.

  22. Paul Banks

    Have been thinking about getting a Kickr Core for a while but put off by the storage space I’d need for it, this looks like it will pack up really nicely and won’t take long to set up each time which is good as I am pretty time squeezed for workout time.

  23. Ian Bowers

    Hi Ray. I saw your comment about the ‘crazy robotic automated calibration’. Does this mean it doesn’t need a spin down or anything. If so that sounds great.

  24. Chris Capoccia

    Are there any special requirements about trueness of the rear wheel?

    • Hi Chris,

      Nothing in particular but we recommend using it with a trued wheel for the best experience. The closer to true the better but there is some wiggle room,

      Scott Cooper
      Product Manager, 4iiii Innovations

  25. Carl

    What are the clearances like? Enough to just run MTB 29×2.3 or gravel 700×40 without swapping tires/wheels? That would be a plus for me, just stick the same bike onto the trainer!

  26. Gytis

    Any info on EU availability and price?

  27. Paul W

    Any word on UK or EU suppliers? It’s not on clevertraining.co.uk.


  28. chufi

    Maybe someone can illuminate what is going on with the max incline simulation number for me? I feel like I just don’t understand the number in relation to the trainers watt number. Going up a grade requires more watts, based on your speed and weight and grade – so doesn’t the ‘max incline’ basically translate to the max watts the unit can produce, and then based on your weight, different speeds would have different max inclines? Do different companies use different reference speeds? It seems like you can find a 2000 watt trainer with a 20% max incline (cycleops hammer direct) and then this one is 2200 watt with a 7% so I feel like I’m missing some fundamental portion of what is going on or not understanding the numbers in the features descriptions. Hardly matters for my skill level, but I like understanding what the deal is.

    • You’re pretty close.

      Max incline for most trainers is based on a given rider weight, usually 70-75kgs for most companies specs. Speed can and does play into things a bit, but honestly that’s a heck of a lot harder to quantify on spec sheets due to variations in gearing. So most companies then demonstrate it as a power curve. Tacx for example has power curves on their site, and I think Elite does somewhere too.

  29. johan de weerdt

    I’m wondering.. how big is the difference with the more expensive trainers in power/ability to train…
    I’m going to start training for Mallorca 312… Will I be fine (73kg..) training with this trainer?

  30. Brian O'Connor

    Tried writing into 4iiii but didn’t get a helpful response on this. I have a 90mm alu+carbon rear wheel – can I use this with the Fliiiight now that I don’t need a rear wheel weight?

    I’ve got a STAC Halcyon, so I’m aware of the alu brake track requirement. I’m just wondering if I need a separate box rim rear wheel, or will the spoke sensor reach down enough to give clearance for a 90mm rear wheel.


  31. TiCoyote

    I got a good deal on a Halcyon on clearance. I like it, but the wheel weights and the centering are a bit of a hassle. I particularly like how it doesn’t put any wear on my tires, it’s quiet, it doesn’t shake the whole house, and it folds up to fit under the couch. I remember in your review of the Halcyon, you found that the ride feel was pretty good. Comparable with a $600 trainer, but not an $800 trainer. Here, it seems like you don’t quite feel that the Fliiight is as good as other $600 trainers. Is the ride feel of this worse than the Halcyon (perhaps because of the removal of the wheel weights), or is it simply that other $600 trainers have dramatically improved?

    I guess my question is, is this a worthwhile upgrade from the Halcyon?

  32. PaulW

    Well here we are in late October. Any sign of these units, or a full review?

    Anything from 4iiii or CT about UK/euro availability?

    I’m signed up on the 4iiii site for updates but they haven’t sent me anything about ordering – anyone else?

    I’m keen! It’s cold and wet in the UK and I live in a top floor unit so this is really my only option. I’ve been looking for second hand Stacs but there are none here.

    Thanks, Paul

  33. TiCoyote

    I’ve been wondering, why doesn’t the company produce a weighted wheel that goes on the bike (flywheel)? It would be easier than the weights, and simpler than the robots and software.

  34. Paul W

    I see CT US now allow you to buy this with a note saying ‘Processed For Shipping in 5-7 Business Days’.

    I’ve not heard anything from 4iiii themselves – and I’ve signed up with 2 different email addresses.

    UK/EU news would be welcome, but I’m in the US in early December so might try to get one delivered to my hotel over there and bring it back myself.

    • Typically when CT transitions to 5-7 days that means they have tracking details from a manufacturer for the shipment inbound to them (or, very recent confirmation that a shipment is being prepared).

  35. Edward

    Hey. The final version is out there. There is a launch in Toronto. Please test the production unit.

  36. Lance

    Today on Clever Training they have the Fliiiight with HR bundle at 499.99. Thats 100 LESS than buying just the Fliiiight by iteslf! and with the DCR discount total is 449.00. Now if 4iiii can just agree on a shipping date………

    • Bryan

      Thanks Lance! I ordered over the weekend and was able to cancel and get this deal today. You saved me $100 and got me a free HR monitor!

    • Paul W

      Darn the discounted HRM bundle page is still showing when you search but gives ‘page not found’ when clicking through. Anyone had their order confirmed? I see Ray had an issue with it this week…

    • Yeah, the ‘deal’…was…uhh….not quite planned. Congrats to those who got it, CT is of course honoring your early Christmas Deal. 🙂

      But…pro tip, the CT VIP Sale starts later this week, which gets you 20% off a single item – and you can use this code right now (FREEVIPDCR) to sign-up for the VIP program for free rather than paid. That way you’re good to go as soon as that opens shortly…very very shortly.

      Sign-up Link: link to clevertraining.com

    • Lance Classen

      At 20% off, that brings a few direct drive trainers back into my range. I am loving the silence idea with the Fliiiight, but in comparison with my gen 1 KICKR I’m sure that anything else is considered quiet by comparison. If the 4iiii doesn’t ship reasonably soon I may change my order…..

    • Paul W

      Excellent, thanks Ray!

    • Bryan

      It was good of them to honor the deal for me. I am very excited to get my first trainer and get back on my bike! I know it’s a gamble going with the Fliiiight without a thorough review but it was too good of a deal to pass up.

  37. Lance Classen

    Paul, where did you see that Ray had issues with it this week?