It’s always good to see new companies enter the smart bike trainers market. STAC did it with a different thinking. If you are looking for a quiet trainer, that is also light, portable and works with Zwift and TrainerRoad, the Halcyon might be for you!


  • Very quiet
  • Battery powered
  • Consistent power reading
  • Quick to respond to changes
  • Doesn’t require calibration
  • Very light and easy to carry


  • Some assembly required
  • You have to add wheel weights for a better road feel
  • Road feel

STAC Zero makes the quietest trainers in the market. That’s because essentially nothing is touching your bike, and there is no flywheel with magnetic resistance or anything mechanical like other direct drive or wheel-on trainers. After the initial release of their STAC Zero trainer, they decided to get into the smart trainer business and started working on what is now the Halcyon.

STAC sent me the Halcyon to put it through my testing and review. Just like I do with all my trainer reviews, I like to spend quality time on each trainer and put it through my real training. This gives me the opportunity to get familiar with each trainer and its nuances. Having so many trainers in my house is like having a lot of kids. Everyone is unique and special in their own way!


  • PRICE: $800
  • MAXIMUM POWER:  2,000 watts at 50mph (72 kph)
  • MAXIMUM SLOPE: Up to 7% slope
  • BATTERY LIFE: 10 hours
  • Weight: 22 lbs (10 kg)
  • ACCURACY: +/-3%
  • BIKE COMPATIBILITY:  The Halcyon is compatible with MTB, Road bikes, TT bikes, bikes with disc brakes, quick release and through axle adapters. The trainer works only with aluminum wheels.
  • CONNECTIONS: ANT+ FE-C compatible, Bluetooth, and Bluetooth FTMS
  • NOISE LEVEL: Very Quiet
  • METRICS: Transmits power and speed
  • APP COMPATIBILITY: STAC works with Zwift and  TrainerRoad in Bluetooth and ANT+ FEC



My first impression with the STAC was how small and light the box was when I got it in the mail. I got used to seeing trainers in big and heavy boxes. I am sure the DHL guy didn’t mind that either.

Once you take it out of the box, you need to check the magnets for alignment and install the wheel weights. STAC did a thorough job outlining all the steps in the manual and also they have some videos. I encourage you to watch these videos to make sure everything is set up correctly.

The magnets are placed in its storing/shipping position and you have to remove the rubber bands and put the magnets back in place.

Once you rotate the magnets to their operating position, they should click in place.

Then there is a little motor assembly that you need to do. All the tools you need and instructions are included in the box.

Once everything is tightened, the next thing you need to do is install the wheel weight. Wheel weight is optional but highly recommended. This process took me around 10min the first time and maybe 10 min again the 2nd time I did because I had to go and rewatch the videos again. I might not be the fastest learner out there but I wouldn’t want to remove and reinstall them again. It’s like installing a cassette, I can do it in a couple of minutes but do I really want to do it?

STAC claims it should take about a minute once you get used to it. Their office record is 30-seconds which is impressive. But the process should get easier if you do it often enough.  As long as you remember which side the screws need to be on and how to attach the two pieces together, there isn’t much to it.

Finally, once you set up your bike and center it, you should check to see if the magnets or wheel calibers are touching the rim evenly. If not, then you can adjust the alignment of the magnets so they are both touching the rim evenly.

You can use the STAC mobile app – available for iOS and Android – to check your installation and magnet position.


STAC Halcyon works with Zwift and TrainerRoad in both ANT+ FE-C, Smart Bluetooth and FTMS. Since the Halycon is FTMS compatible, this makes it compatible with even more apps such as The Sufferfest.

You can also connect and control the trainer with any Garmin EDGE that supports ANT+ FE-C protocols and be able to simply use your Garmin to adjust resistance.


STAC includes wheel weights with the Halcyon that you need to install on your own wheel. Any aluminum wheel should work. However, if your wheel has a steel pin in it, it won’t work. Also, the Halcyon doesn’t work with carbon wheels.

I found the Halcyon to feel ok when in ERG mode, however, when in sim mode and on an incline, it didn’t feel as good. You will feel some dead spots when pushing down the pedal or around the 4 – 5 o’clock the pedal revolution. The steeper the incline the more magnified those dead spots felt. On the flats, it felt ok and you will have a lot of momentum and freewheeling when going down descents.

In the STAC app, there is a road feel optimization setting that you can play with to find the best option for you. The company offers additional weight for $25 that you can attach to the current wheel weight that might improve the road feel for you.


STAC measures power differently from other powermeters. Traditional powermeters such as a hub base or crank base measure power from all directions as you pedal. However, STAC measures power in one direction and it’s tangential to the wheel. So you will find power reported by the Halcyon to be a lot smoother and consistent.

Here is the data from Zwift NYC Tour stage 2. The power from STAC wasn’t that far off and was moving along with my other two powermeters on my bike. For the full ride, STAC was only off by about 12 watts normalized and 6 watts average power. That’s about 5% higher than my powermeter when looking at normalized power.

Halcyon Power2Max Watt Diff (Halcyon vs P2Max) % Diff (Halcyon vs P2Max)
Average Power 196 202 -6 -3%
Normalized Power 230 218 12 5%



In ERG mode, the trainer started off very close to my powermeter but then made some separation when getting into the intervals. It’s possible my Power2max wasn’t calibrated at that time and was reading a little higher which isn’t unusual.

Time to geek out a little here. Smart trainers react differently in ERG mode. Usually, the software sends power target to the trainer and the trainer will make small adjustments to keep you at that target power. These small adjustments usually result in small power fluctuations. These fluctuations vary between trainers. Usually, the higher end models react better.

For example, here is a 10-minute section from a high-end trainer. No, it’s not the trainer you are thinking about but it’s one of the higher end ones that cost over $1,000. I removed all the smoothing and the source of this data is my powermeter. The reason I am showing you my powermeter is to remove the trainer from the equation and the possibility of any power smoothing done by the trainer. So this data was directly from my crank-based powermeter: Power2max.

This ride was done on a high-end trainer in ERG mode. Power source: Power2Max

The average for that ride was around 238. Close enough to my target of 240 watts. You can see how the trainer was adjusting the resistance to keep me at 240 and resulting in a very scattered line.

Here is another scattered dot chart with no smoothing to see how power was scattered all over the place.

This ride was done on a high-end trainer in ERG mode. Power source: Power2Max

Now, let’s take a look at the Halcyon. The following graph is for a 15-minutes segment on the Halcyon in ERG mode. The source of this data is my crank-based power meter: Power2max. You can immediately see how smoother the line is. This means the Halcyon was better at keeping my pedal stroke smoother and not having to continuously react to power changes resulting in a smoother line.


This ride was done on STAC Zero Halcyon in ERG mode. Power source: Power2Max

Here is a scatter dot chart of the same ride and it’s ridiculously smooth:


This ride was done on STAC Zero Halcyon in ERG mode. Power source: Power2Max

Not sure why the difference or how STAC does this better than other trainers but wanted to mention this in my review.


It’s always good to see new companies enter this market. STAC did it with a different thinking. The trainer can be a little intimidating to some but if you are the kind of person looking for something different and like to see how things work, the STAC might be for you. I would also recommend the Halcyon to anyone looking for a portable, lightweight, and a smart trainer to take on the road or take on a plane.

STAC wanted to give athletes the ability to use their own wheel. However, many might find it a little bit of a hassle to install and remove the weights or might not want to install them on premium wheels and possibly risk damaging the spokes even though I haven’t seen reports of this happening to anyone.

STAC sells for $800. That’s around the midrange direct drive trainers. If they can bring the price down a couple of hundred dollars and price it around the wheel-on trainers, I think they might attract more customers and especially people who are looking for a wheel-on trainer that is silent and portable.

Finally, you can find the STAC Halcyon at STAC and you can also purchase it at CleverTraining.

Thanks for reading!

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  • Hi, I am looking for a light portable trainer I can bring on short business trips for some Trainerroad intervals training. Needs to be something with a quick set up, compact and light. I was considering the Halcyon (without the wheel weights). The Omnium would also be an option (but no power control)… What would you recommend? thanks

    • The Omnium is the best portable trainer IMO. If you have your own power meter and can train without having all the smart functionality, then you would enjoy the Omnium. Plus it comes with a travel bag too. If you need a smart trainer, the Halcyon is a good portable and light trainer.