stac zero indoor cycling trainer that doesn't touch your wheel or tire

The STAC Zero indoor cycling trainer brings three very unique features to market. The most eye catching is the resistance mechanism, which doesn’t touch your wheel. Or your tire. Or require wheel removal, as on direct-drive trainers. Instead, it uses two banks of magnets to create resistance on your alloy rims. That means no moving parts, and no noise…which is the second innovation. It’s totally quiet. The only noise you’ll hear is your drivetrain. The third innovation? It packs down really, really flat…

stac zero indoor cycling trainer that doesn't touch your wheel or tire

The resistance unit slides up and down to adjust for wheel size, and you can angle the magnet banks in or out to adjust for rim width. It’ll fit around road, cyclocross and even mountain bike tires.

stac zero indoor cycling trainer that doesn't touch your wheel or tire

A speed sensor is integrated into the design, and the lower body of the resistance unit is a strain gauge. Combined, they calculate your power output and transmit that figure via ANT+ and BLE to your cycling computer.

stac zero indoor cycling trainer that doesn't touch your wheel or tire

When you’re done, it folds completely flat, low enough to fit under many couches. It’s also fairly light since there’s no flywheel or fluid unit. They include a 2lb weight that clips into your rear wheel (if you want) to give it a little more momentum so it “coasts” more naturally between pedal strokes. Technically, it does contact your bike at the axle, but that’s it. There’s no tire wear or moving parts to wear out.

Retail is $399 for the standard unit, $499 with power measurement.

STACzero.com

27 comments

  1. Veganpotter on

    I’d love to try this to feel how realistic it is at different outputs. That said, this isn’t actually new. Maybe it’s just now headed for retail but this looks very similar to their unit from two years ago but I can’t recall if that was a prototype

    Reply
  2. chinoDCR on

    I read an article about this earlier this year, back then you had to attach either metal “strips” or magnet “strips” (I don’t recall) to the rear wheel for it to work, is this no longer the case?

    Reply
  3. MaxG. on

    yeah 2k would feel like a stick thru the spokes for me.
    Hopefully it is down adjustable or the high intensity training would set a new all time high.
    But seriously this super simple quiet design just seems to good to be true, whats the catch?

    Reply
  4. B P on

    How do the magnets work on aluminum alloy rim? It isn’t magnetic.

    Also, where does the energy go? It’s got to build up heat, or supply power back to the grid…which is it? There’s not a whole lot of mass, or surface area there to dissipate heat.

    Reply
    • Robin on

      Eddy currents come from, in the case, the motion of a conductor (aluminum) between magnets. The net result is a magnetic field is generated in the wheel that opposes the magnetic field of the magnets between which the wheel. The generated magnetic field opposing the magnetic field of the magnets is what produces the resistance a rider on the trainer feels.

      Reply
  5. Cryogenii on

    Unless they are trying to use eddy currents in the metal of the rim to provide the resistance. But pumping up to 2000 W of power into your wheel would get toasty!

    Reply
    • Art Hare on

      STAC Guy here…

      It indeed gets your rims hot – but for normal riders (aka not 2000W riders) the rim tops out at 60-70C. It is hot, but not dangerously hot. Remember – more power requires more wheelspeed, which means more airflow for cooling. It was one of the things we worried about when designing it, but fortunately it turns out you can put 300W into a wheel moving at 40km/h without it getting too hot.

      Reply
    • Robin on

      All that’s needed is a wheel that’s a conductor. The magnets between which the wheel spins will generate a current in the wheel which will in turn generate a magnetic field that opposes the magnetic field of the magnets. That’s the source of trainer’s resistance.

      If you want to verify that you don’t need a magnetic metal, buy a sizable neodymium magnet and a copper aluminum tube that’s only slightly larger. Drop the magnetic down the tube, and the magnet will fall more slowly than expected. That’s eddy currents at work. If you don’t want to buy the stuff needed for that experiment, search YouTube for “copper pipe neodymium magnet.”

      Reply
  6. jim on

    if you don’t want 2K watts you can adjust for less by making the gap between wheel and magnet a little bit larger. Only issue, maybe, is if your wheels are out of true.

    If you could adjust the gap between magnets and rim on the fly you’d have a smart trainer, not sure about measuring the resistance though ?? (anybody ??)

    Reply
    • Scott on

      There are a number of companies that make thru axles designed to be used with trainers. Google “Robert Axle Project” for example.

      Reply
  7. Dinger on

    Very cool concept! I am only a little familiar with this. Does the mass of the alloy rim have a significant effect on the power of the magnetic field generated?

    Reply
    • Robin on

      If we consider each rim wall a sheet, then the power lost thru the eddy currents varies directly with sheet thickness but inversely with the density of the sheet material. So aluminum rims with thin walls will dissipate more energy than iron rims with thick walls.

      Reply
  8. phutterman on

    This is the same idea as those roller resistance units that put a bar with some strong magnets on it near one of the (alloy) roller drums. I DIY’ed one once when I had rollers but no trainer. It didn’t have either the precision or strength to create that kind of resistance. This strikes me as pretty clever if the feel and resistance is good enough.

    Reply

COMMENT HERE: (For best results, log in through Wordpress or your social media account. Anonymous/fake email comments may be unapproved or deleted. ALL first-time commenter's posts are held for moderation. Check our Comment Policy for full details.)

This site uses Akismet to reduce spam. Learn how your comment data is processed.