Online bike calculators

[mfezela]

This looks useful, especially the Gear Calc and Stem Comp Calc pages on this site and linked GeometryCalc.

http://www.yojimg.net/bike/web_tools/

[mfezela]

And this

https://www.bikegeocalc.com/

[atk]

https://bikeinsights.com/ is quite good too