Explanation of Fit Calculator Output Values Top Tube Range
This measurement is along the top tube, from the midpoint at the seat tube to the midpoint at the head tube. No single piece of frame geometry has a greater impact on comfort than your top tube. If you plan on paying attention to one measurement and one measurement only, make it this one. Keep in mind that we do not measure the actual top tube on bikes with compact frame geometry. Rather, we use an “Effective Top Tube” measurement - an imaginary line drawn parallel to the ground along the length of the top tube.
Stem Length
This measurement indicates your ideal stem length. It takes into account that your stem will be flipped to its flatter angle (e.g. 80° for Deda, 84° for Ritchey).
BB-Saddle Position
This measurement is along the seat tube, from the center of the bottom bracket spindle to the top of the saddle. It is an ideal starting point for saddle height. Given the varying differences of cleat and pedal heights, and given the varying differences in the thickness of saddles, the BB-Saddle position has a broad range of 2cm.
Saddle-Pedal Position
This measurement is closely related to your Saddle to BB position, and in many ways serves to redundantly confirm that your saddle height is in its ideal initial range. Move your driveside crankarm downward until it’s parallel with the seat tube of your frame. Measure from the center of the pedal axle along the seat tube up to the top of your saddle. Please note that this figure is not an absolute, since your personal choice of pedals, shoes, and saddle – not to mention your muscular flexibility – all have an impact here.
Saddle-Ground Position
The Saddle to Ground measurement is not made along the seat tube. Rather, you’ll need to measure from the top of your saddle (at its midpoint) straight down to the floor. This is another measurement useful in establishing your initial saddle height position. Use this to complement the Saddle-BB and Saddle-Pedal measurements.
Cranklength
Few topics can fire up a debate quicker than “What’s my ideal cranklength?” We aren’t shattering any paradigms with our recommendations here. Rather, we’re sticking with the traditional criteria for suggested cranklength. Generally speaking, cranklength is a function of femur length. The longer your femurs, the longer your crankarms should be. Long-legged people, the conventional wisdom states, should take advantage of their inherent leverage by choosing longer arms. Conversely, short-legged people are traditionally steered towards maximizing pedaling efficiency through high RPM’s and relatively short crankarms. Googling this topic will possibly provide nearly as many results as “Does God Exist?”
Aero Bar Size
Many aero bars come in one length only, but have adjustable extensions so you can customize their fit. In contrast, many other models come in multiple sizes, requiring you to choose a specific length (just as you would a stem). Our size recommendation here is designed to give you an good weight balance and the start of a high-quality aero position.
Saddle-Aero Bar Pad Drop
It’s a cliché in multisport, but behind every cliché is a kernel of truth: “How low can you go?” The lower you can position your aero bars, the lower your drag becomes. With lower drag you squeeze more speed out of every watt of your pedaling power. The reality of aero fit, though, is that you can only go so low before your body ends up in agony – and an agonizing position is useless since you won’t maintain it.
Two factors generally dictate how low you can/should position your aero bars. First is your flexibility. If your hamstrings are nicely flexible it’ll allow you to reach further down to your aero bars for a delightfully wind-cheating tuck. Conversely, if your flexibility is lousy your aero bar pads are more ideally positioned at near saddle-level or else you’ll end up squirming and contorting yourself upward into an inefficient and ultimately non-aero position. The name of the game is to get into the most aero position you can maintain for the length of your race. Aero for half, then exhausted and non-aero for the second half is a losing proposition.
The next factor in choosing a saddle-to-bar drop is the nature of the event you’re training for. Longer events require a more tolerable body position. Slamming your bars down as low as they go isn’t a smart strategy for an Ironman-length ride. Sometimes making aero sacrifices in order to conserve energy is wise so you can finish the bike leg with decent strength and make the run a less daunting task. The opposite is also true, of course. For a short Tri or a brief TT stage in a stage race, aero is everything. In an Olympic distance (or shorter) Tri, you likely won’t kill your run by making big positional demands from your body. Likewise, in a TT you don’t have a run leg to worry about, so red-lining yourself (not just from the standpoint of power output, but positional aggressiveness) is the right tactic.
We provide you with four options in saddle-to-bar drop. This specifically measures the differential between the high point of your saddle and the touch point at the center of your aero bar pads. Each option is increasingly aggressive. While your aerodynamics improve with each position, you’ll feel increased stress on your body in maintaining each position.
Pad-Ground Position
This is the corollary to your Saddle-Aero Bar drop. As this drop increases, the distance from your aero bar pads to the ground will decrease. Measure from the top of the pad at the leading edge of your aero bars directly downward to the floor. Use this measurement to help dial in your ideal aero position, and utilize it alongside your saddle-aero bar value when you finalize the initial fit of your new bike.