The world of bike fit is a large and expanding one. Just over a decade ago, rigorous fit systems had barely begun to emerge in the world of road fits, and there wasn't a single protocol on the planet to systematically define a TT or tri bike fit. Now, there are several fit systems in competition, each with a proprietary fit protocol: Specialized BG Fit, Serotta (SICI), Slowtwitch (F.I.S.T.), and Retul.
The very first article ever written here on TriRig was a user-centric review of a Retul fit. That is, I talked about how the technology operated from the perspective of an athlete going in for a fit at Retul. In this article, we come full circle, and I'll describe what Retul means from the fitter's perspective. In March, I completed the Motion Analysis Certification course at Retul University, and thus became a certified fitter. So now I can perform Retul fits. But for the upshot for the TriRig reader is that you'll get a much better understanding of what Retul is all about, inside and out.
For the moment, we're going to ignore the differences in fit protocol � that is, how and why the various bike fit methods actually prescribe your fit coordinates. We'll get to that a bit later. For the moment, I want to talk just about the technology.
Traditional bike fitting was done with a goniometer (a kind of protractor to measure body angles) and a plum bob to measure setback. Some use video analysis, using a freeze-frame capture to get a picture of your pedal stroke and measure the body angles there. What makes Retul so awesome is how it captures a picture of you, the cyclist, actually riding the bike. It takes real-time measurements as you actually pedal under load, and averages your body angles during certain portions of the pedal stroke over a span of time. This gives the fitter both an extraordinary amount of data points, and those data points are arguably much more valuable than if they had been gathered with a static rider being measured with a goniometer.
But the guys at Retul are quick to point out that one of the most important aspects of its collected data is that it's done in three dimensions. The Retul capture device (the current version is called the Vantage) has four sensors that each have a slightly different perspective view of the marker dots. This allows the system to construct a complete three-dimensional picture of the rider. Not only does this allow for some really interesting and useful metrics to be captured (like your lateral knee travel and pedal stroke pattern), but it again lends more integrity to the data gathered. An optical capture from a side-view camera will suffer from lens distortion and perspective distortion. Retul will get your angles right on the money, and is immune to distortion. You don't even have to set the rider perfectly perpendicular to the Retul itself - it will find the correct plane of measurement based solely on the marker positions in 3D space.
Now, it bears mentioning that no matter what technology is used to observe fit metrics, the fitter's eyes and expertise are still the most important tool in the job. A good fitter will often be able to estimate most angles within a few degrees just by naked-eye observation. But the key phrases there are �often� and �a few degrees.� Many of the acceptable ranges in a Retul fit are only five degrees. For example, your angle of knee flexion is to fall within 35 and 40 degrees. There's no substitute for an actual measurement, taken under load while riding. With that in mind, let's talk about the next component of Retul as a complete system, which is their fit protocol.