This is an excellent site created by Tom Compton.
“Analytic Cycling provides technical methods for evaluating and estimating cycling performance and parameters. It makes extensive use of differential equations and advanced numerical methods.”
Some of their calculators I’m still trying to learn how to use or gather the needed information for input. Some of this is very technical.
Here is an example of just one of the many online calculators available. The following is a quote from their web site. This one is called Long Climb. “Let’s say a rider is planning a long tour with lots of long climbs at the end of some tough days. The rider wants to be sure to have a gear that is low enough. The rider estimates that the steepest climb will be 8% at a worst-case speed of 1.75 m/s. The rider can maintain a 45 cadence at this speed. What would the suggested gear be? The following table suggests a 39×28, the lowest one the rider has, but not as low has he wants. Maybe the rider should consider a triple. Good advice: “Take your low gears.” ”