On my Bike Tinker blog, I have a Google Doc for calculating optimal tire pressure.  This is the web widget I designed to replace that. It is much easier to use, and I won't have to maintain it at all.

It gets a fair amount of traffic, and people often delete or damage the functions. Some people add features, like "trailers," or "kg/bar" conversions, which is cool, but managing the document is tedious, and usability could be better. If usability was optimal, then people wouldn't break it, right?

The next step will be a mobile app that allows for saving multiple bikes. Maybe it can talk to Cyclemeter to show performance changes at different pressures...