In its most basic sense, a bike fit is a very simple thing. It's two sets of coordinates, measured from an origin at a bike's bottom bracket. The first set of coordinates locates the bike's saddle, and the second set locates the armrests. Assuming you're using the same aerobars, the same pedals, and the same saddle, you could take those coordinates to any bike and replicate your fit identically, time after time. Of course, ride characteristics and aerodynamics of the bike itself will change. But your fit would stay the same, if you kept those coordinates consistent.

The problem is that replicating a bike fit is often not that simple, because people will tend to change their saddles, pedals, and aerobars. And even the pros need help making sure everything lines up the way it used to when they switch to new equipment. Such was the case with Mary Beth Ellis, who got her new Kestrel Airfoil Pro dialed in at the Retul studios this week. The case with Ellis is an interesting one, and hinged on a saddle she had changed. On her old bike, an Adamo Podium saddle provided the position she wanted. But her new Airfoil Pro had an Adamo Race saddle mounted up. That saddle is very similar, but has some notable changes that we've reviewed here on TriRig.

Specifically, the saddles ride differently due to their different contours. Even if you match the saddles so they are at the same stack, they provide a slightly different position. That difference was enough for Ellis to notice. For a pro athlete so tuned into her own position, a difference of only a cm or so can raise a red flag. The solution, in the end, was the simple one: put Ellis back on her Podium saddle and remove the Race model. It would have been possible to keep tweaking the fit with the Race saddle, but Ellis prefers the Podium anyway, which made the choice an easy one. Retul's Zin tool allows the fitter to make a precise measurement of exactly where the saddle sits relative to the bottom bracket, both in terms of its location and its angle. So after a quick Zin of the situation, fitter Mat Steinmetz had Ellis back on her ride, ready to take some names at November's 70.3 World Championships in Clearwater, Florida.