I made this tool for motorcycles, but it is easily flexible enough to work for bicycles and even wheelchairs, trikes, etc. It allows you to enter known dimensions (rake, fork offset, wheelbase, tire diameters; trail is calculated) and planned changes to any of those figures (plus some others, like stretching the frame). It renders a schematic representation of the two on top of each other and provides numeric output of the new rake, trail, wheelbase, and some other numbers useful for building a frame jig or estimating handling effects. As a bonus, the data inputs are encoded in the url, so you can save / share designs just be saving / sharing the link. The code executes 100% client side; the url change is to the hash, with no new request / data exchange.

https://sebwiers.github.io/motorcycle-front-end/