Note: Screenshots taken from version 2.0, around October 2009.
Gear and Crank selection
This page lets you select your bike's Chainring and Sprocket Size. Specify the length of your cranks. Bike Gears will calculate the corresponding Gear Ratio, Gain Ratio, Development, etc.
This page lets you select your bike's tires. Tire size influences the distance you travel as well as your speed.
Select from over 200 standard tire sizes: 16", 17", 18", 20", 25", 26", 27", 700c, tubulars, etc.
Also, you can measure your rear tire rollout and enter it in millimetres or inches.
— Finepics - Version 2.0 - 7-Oct-2009
Skid Patch Visualizer
Your fixed-gear bike's gear ratio determines which parts of the rear tire suffer the abuse of skidding (skip stopping). The Skid Patch Visualiser shows you where the patches are located on the tire. It also takes into account if you're an ambidextrous skidder or if you always skid with the same foot in front.
— f***ingstupid - Version 1.0 - 29-Jul-2008
How fast can you go? This tool can give you a good approximation of how fast you can go, considering your gears and rear tire.
You found the perfect gear ratio, but your local bike shop doesn't have 47T chainrings in stock? Have no fear, Bicycle Gear Calculator will propose alternate configurations that are as equivalent as possible to the original one in terms of gear-inches. You can also use this tool to find a chainring/sprocket that offers more skid patches, to prolong your rear tire's life.