- Translating Fit Specifications to Bicycle Specifications -

1. SADDLE POSITION:

Saddle Vertical distance from the BB will be called SY.

SY is calculated by getting the reading from the saddle vertical stainless steel slider (in this example it is 607mm) and adding the distance from the top of saddle horizontal railing (the black piece with a horizontal scale) to the horizontal line from the tip of the saddle to the back of the saddle.
The saddle must be horizontal at all times! Or the max discrepancy can be some 2mm up or down, on the front/rear end.

Saddle Horizontal distance from the BB to the tip of the saddle will be called SX

SX is calculated like this:

The actual reading from the black horizontal railing (in this example, 125mm) minus the distance from the tip of the saddle to the reading mark on the black glider (where the saddle is attached) - we'll call that one SH.

You can measure SH by placing a 90Deg triangle on the railing, lining it up with the seat tip at the same time.

SX can be positive (saddle tip is at the front of the BB centre) or negative (saddle tip is behind the BB center)

So, saddle position is determined by three parameters:

1. SY - Vertical distance from the BB
2. SX - Horizontal distance from the saddle tip to the BB
3. The type of saddle. The type of saddle is essential, as some of them have longer railing and can accommodate only certain seat tube angles.

2. HANDLEBAR POSITION:

When we talk about handlebar position it is actually the center of the handlebar stem opening (where the handlebar is clamped into the stem) that is the main point of interest. Of course that type of handlebar is essential for the total bike fit, but in case of determining base/critical handlebar position - only the center of the stem opening matters.

Handlebar Vertical distance from the BB will be called HBY.

HBY is calculated by getting the reading from the handlebar vertical (stainless Steel) slider (in this case it is 498mm) and adding the distance from the top of the handlebar horizontal railing (the black piece with a horizontal scale) to the center of the handlebar stem opening (where the handlebar is clamped).

Handlebar Horizontal distance from the BB will be called HBX

HBX is calculated like this: if the stem is pointing forward (which will happen in a majority of cases) - the actual distance is the reading from the scale on the black handlebar railing (in this case 390mm) plus the stem length (in this example 90mm). A total of 480mm. If the stem is pointing back, stem length should be deducted from the actual reading.

So, the handlebar position is determined by two parameters:

1. HBY - Vertical distance from the BB
2. HBX - Horizontal distance from the BB

For more insight about translating specifications, you can go to this slowtwitch.com article.