Examining the Science behind Bicycle Performance
Analytic Cycling: Set of tools for calculating cycling performance based on a large number of variables
BikeCAD at The Bicycle Forest: Design your own frameset & bike. Outputs drawings, miter templates, etc. for building your frame.
Wind Tunnel from Algorizk: Very cool app for iphone or ipad. Explore aerodynamics of various 2d geometries.
Disclosure: Please note that some of the links below are affiliate links and I will earn a commission if you purchase through those links (at no extra cost to you). These are all things that I have experience with that I am recommending because they are helpful and are resources that I trust, not because of the commissions that I may earn. Please do not spend money unless you feel it’s for something you really need and will help you.