Step 1: Find your arm pad fit coordinates: Stack (Y) and Reach (X) measured from the back of the pad on your current bike.
Step 2: Lookup your frame stack and reach on either the dealers website or on Slowtwitch.com
Step 3: Note how many spacers are included between the stem and the frame. This number includes the headset cap.
51 SPEESHOP MONO-RISER AEROBAR GEOMETRY
Your frame stack (including spacers & top cap) + 82mm + spacers in 5mm increments until desired stack height is reached = Your mono-riser stack position.
Your frame reach + 4mm + 12.5mm pad increments until closest pad position is met = Your mono-riser reach position.
Ex. Cervelo P3 size 54.
Rider Fit Coordinates
Armpad Stack: 630mm
Armpad Reach: 450mm (back of pad)
Cervelo P3 (size 54)
Frame Stack: 522 (537 including spacers)
Frame Reach: 411mm
Spacers: 10mm top cap and 5mm spacer (15mm total added to frame stack)
Doing the math...
Frame Stack (537mm) + Minimum Bar Stack (82mm) = 619mm* + 10mm mono-spacer = 629mm
*To achieve the desired pad stack of 630mm, you would add a 10mm mono-spacer to the bar for a total pad stack of 629mm. From there, whatever spacers you choose to remove from the steerer tube (stem spacers & reduced top cap) can be added as a mono-spacer to the bar.
Frame Reach (411mm) + Minimum Bar Reach (+4mm) = 415mm* + 37.5 (3x12.5) = 452.5mm
There is 50mm of total reach adjustment in 12.5mm increments
Option 1: 415mm
Option 2: + 12.5mm = 427.5mm
Option 3: +12.5mm = 440mm
*Option 4: +12.5mm = 452.5mm
Option 5: +12.5mm = 465mm
*The desired armpad reach coordinate is 450mm making Option #4 (452.5mm) the best fit option.
Visual of math exercise