Note the difference between this approach and the systems we often see today where your position is established while riding a fit bike. These fit bikes have been around for decades and they really were not made, in the beginning, as a tool aboard which you pedaled, under load, while your position was established. Rather, you could take something like BG101, or the Fit Kit
system more than 30 years in use. You could, if you wanted, establish a position aboard a fit bike, maybe like the Waterford Fitmaster, and you'd have underneath you a "bike" that you could set up via quick releases that allow you to "build" a top tube of 56cm, down tube of 57cm, various seat and head angles and so forth. The bike, thusly built, is then measured and you match this against the bikes you have in stock (if you're a bike shop) or you give that data to a custom bike maker. This was all very analog. This stands in contrast to what we have today and it might help to differentiate between the traditional use of fit systems and tools and a more recent way of approaching bike fit.
There are 3 ways to parse between these older systems versus with what we've now got today (Retul, Guru, F.I.S.T., etc.).
1. When you take limb and torso measures and generate an "output" that's either an exact model (Cervelo R3, 57cm, 110mm stem –6° pitch), or a general parameter (any bike with a 58cm top tube and 57cm seat tube), you're relying on a STATIC fit process. When you actually pedal aboard a fit bike and the process of riding is incorporated into the selection of fit coordinates (seat height, cockpit distance, handlebar elevation) that's a DYNAMIC fit process. When we talk about software for bike fitting, it's important for you to determine whether the process the software relies upon is static or dynamic. If you don't have a fit bike and you don't intend on getting or using one, a piece of software that optimizes a dynamic process is probably a waste of money. Maybe the software only refers to taking fit coordinates and giving you back complete bike solutions. Software like this mates with any kind of process – static or dynamic – that outputs fit coordinates. (The software you have access to via this article is this kind.)
2. The software sold by Fit Kit will tell you the seat and top tube lengths of the bike you're looking for. It's designed to be used by bike shops that just can't or won't or choose not to move to an X and Y system of bike and fit metrics. The Waterford Fitmaster bike "looks" like a bike, with its seat and head tube members declined back from vertical, just like a bike you ride. This differs from fit bikes that adjust straight up and down and back and forth. Measurements like seat tube, top tube, head tube, head angle, seat angle all are based on what we'll call an ANGULAR approach to bike metrics. In order to know where the head tube top sits in relation to the bottom bracket, you must know the bottom bracket drop, seat angle, seat tube length, and top tube length. The other way to identify the head tube top relative to the bottom bracket is via stack and reach, and these are the X and Y (horizontal and vertical) distances between those two spots. Fit Kit, Waterford and others are angular in their approaches, and that's really the bike business up ‘til 10 or 15 years ago. A more recent approach is to look at dimensions like BB to head tube (stack and reach) or BB to handlebar clamp, or BB to armrests (for tri bike fitting) and this "X/Y" approach is the alternative to the angular approach.
3. Finally – and this is important when you choose software – there are 2 parts to the fit process. Part 1 is the establishment of fit coordinates (seat height, handlebar elevation, etc.). Part 2 is where you match those fit coordinates to complete bike solutions. Images here are of the Guru fit report that show, among other things, your complete bike solutions.