Whether they use fluid, fans or magnets to create resistance, most stationary bicycle trainers require users to place the bike's rear tire in contact with a roller. This wears the tire down quickly, and creates a lot of noise in the process. Canada's STAC Performance is out to change that. Its STAC Zero trainer leaves the tire untouched, keeping its rubber intact and the noise level down.
The STAC Zero actually does utilize magnets, although not in the same way as regular magnetic-resistance trainers. Instead, it uses them to create what are known as eddy currents.
One of the manners in which these currents are produced is through relative motion between a magnet and a nearby conductor. In the case of the STAC Zero, the conductor is the spinning aluminum wheel rim, while the magnets sit in two rows on callipers located on either side of that rim. The faster that the wheel spins, the greater the amount of resistance is created by the eddy currents.
"The 'base' resistance level is set by the proximity of the magnets to the rim," STAC co-founder Andrew Buckrell explains to Gizmag. "Beyond that, the power is linearly proportional to wheel speed. If you want to go for an easy ride, you can drop to a low gear and happily pedal away at 150W at 10 km/h, but if you want to do an intense interval, you can shift up a few gears, and at the same pedalling cadence, you can output 600W at 40 km/h or even more."
An included set of weights are attached to the spokes of the rear wheel, to add some revolving weight that gives a more natural "road-like" feel to the pedalling – on conventional trainers, a spinning flywheel serves that same purpose. Because it has no bulky flywheel, incidentally, the STAC Zero folds down to have a very low profile when not in use.
And no, it won't work with carbon rims.
The STAC Zero is currently the subject of a Kickstarter campaign, where a pledge of CAD$349 (about US$273) will get you a basic non-power-meter-equipped model, while CAD$449 ($351) will get you one with a power meter – assuming everything goes according to plans, that is. The planned retail prices for the two versions are CAD$399 and $499 ($312 and $390), respectively.
A demonstration of how the trainer uses eddy currents is provided in the video below.