Review: STAC Zero Eddy Current Trainer
Long-time fans of TriRig will know that I've done a few reviews of indoor trainers, but not nearly as many I've done for other categories of products, like frames or wheels. In some product categories, there just isn't as much innovation that I'm interested in covering. However, when I bumped into the STAC guys at Interbike this year, I was really taken aback. Their new fledgling trainer, born on Kickstarter, was a real, genuine, innovative leap in the trainer market. It doesn't merely use a new gimmick to deliver resistance; it's an entirely-new, COMPLETELY SILENT resistance method which relies on magnetic eddy currents to slow down your wheel without ever touching it. It's not a gimmick, it's not a hyperbolic claim. The trainer is SILENT. It's simply amazing.
I saw the STAC Zero at their Interbike booth and was immediately intrigued. The first and most important question was, how does the thing feel and operate in practice? That's what I wanted to be able to determine for myself, and write to you, dear reader, in this review.
Long story short: the trainer is awesome. But it does take a little care in setting up.
First off, the trainer requires that you use an alloy rim in order to interact with the magnetic field and create that eddy current. And interestingly, not just any alloy rim will do. We tested with Mavic Askium trainers, and also Shimano R500's. Only the Shimano wheel worked. The Mavic didn't properly trip the current, and there was very little resistance. With the Shimano R500 installed, there was an adequate amount of resistance, but it wasn't quite as smooth as we'd like ... until we installed the included Bar Weight, which basically increases the weight of the wheel. Stac says that the Bar Weight is optional, but we found it was really a necessity to achieve the smoothest ride. Once your wheel is set up, and the magnets were carefully dialed in, the trainer was an absolute dream. Smooth, even resistance, and plenty of it, with absolutely no sound from the trainer.
The trainer is also eminently portable, packing completely flat for easy storage or travel. However, that's just the trainer itself. Assuming you're going to use a dedicated rear trainer with the Bar Weight installed, it's a bit less portable.
With a side-by-side comparison of the STAC Zero trainer versus a CycleOps Jet Fluid Pro trainer, we noticed a substantial improvement in the sound that was coming from the trainer. While not accounting for all characteristics of a sound, such as the pitch we were hearing (which changes perceived loudness), we managed to get readings of 64 decibels with the STAC whereas the CycleOps came in closer to 72 decibels. We controlled for as many variables as possible including drivetrain, environment, cadence, as well as power output during the impromptu test. In practice, the STAC sounded less than 1/2 as loud as the CycleOps.
Another great facet of the STAC trainer is that there is no tire wear while in use, which both saves your tire, and accounts for a large component of the noise savings. The other component of trainer noise is the resistance unit itself - again, STAC has no noise related to its resistance mechanism. With the STAC trainer the only noise during use is simply from the drivetrain itself. If you (or those who live with you) want a quieter experience on your indoor trainer, allowing you to focus on your session while buying fewer replacement tires in the process, this may be just the indoor training upgrade that will make that much needed difference for you.