Here is an overly simple guide for making changes to either Saddle Height or Fore/Aft, and the related change in the other direction. Since The seat tube is inclined (around 73.0* on lots of road bikes), you are making a direct and indirect change.
- Change Saddle Height and you are also changing the Fore-Aft position.
- The inverse is also true, that if you change Fore-Aft, you are also changing Saddle Height.
- This has a direct effect on the rider position over the pedals and bottom bracket, but also impacts the reach to the bars.
I am hoping this rough example can help people consider the direct change they want, and the indirect changes that come as a result of the primary change. The specific distances are for the 73.0* Seat Tube Angle. Differences will exist if you have a different STA, but anything close will be reasonable when considering the values below.
Saddle Height Change:
If you change the Saddle Height by 1mm [0.038in], you also get a Fore-Aft change of 0.3mm [0.012in].
Saddle move UP 1mm [0.038in] moves Saddle BACK 0.3mm [0.012in]
Saddle move DOWN 1mm [0.038in] moves Saddle FORWARD 0.3mm [0.012in]