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May 28, 2019, 6:14 p.m. -  Alex D

To simplify this, we can normalize reach and ETT for a desired stack and saddle height. Inputs: * Reach = R * Stack = S * Head Angle = HA * Seat Angle Actual = SAA * Desired Stack = DS * Desired Saddle Height = DH Outputs: * Adjusted Reach = R - (DS - S)/(tan(HA) * Adjusted ETT = ETT - (DS - S)/tan(HA) + (DH - S)/tan(SAA) Adjusted reach is reach for a given stack. Adjusted ETT is ETT for a given stack and saddle height. If you're doing these calculations in Excel or Sheets, enclose each angle with RADIANS(). If a manufacturer doesn't provide an actual seat angle, you can measure it with a side profile of the bike in Photoshop or equivalent. Let's compare (for example) the SB150 and the Megatower and assume these desired values: * Desired Stack: 665 * Desired Saddle: 720 SB150: * ETT: 654 * Reach: 505 * Stack: 635 * HA: 64.5 * SAA: 71.7 Megatower: * ETT: 646 * Reach: 490 * Stack: 643 * HA: 65 * SAA: 67.8 Results: * Adjusted reach, Megatower: 480 * Adjusted reach, SB150: 491 * Adjusted ETT, Megatower: 667 * Adjusted ETT, SB150: 668 For this hypothetical rider, once the saddle and bars were set up, we'd expect identical seated positions and about 1cm more room standing from the SB150.

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