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.
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.