Here’s another cycling app for the Android that I have been using recently – especially since I’m (still) in the process of turning my old steel road bike into a fixed gear.
Fixed Gears is a very straight forward and useful app for calculating pretty much anything you would need to calculate in relation to building a fixed gear. Input your crank arm length, chainring and rear cog and it will tell you your Development (the distance your rear wheel advances for one revolution of the crank), Gear Ratio, Gain Ratio, Gear Inches, and Skid Patches.
Another tab lets you input your tire size, which will allow you to calculate your speed based on what cadence you select on a slider bar.
Probably the tab I found most useful is the Alternate Gearing tab. This will show you all of the possible chainring/cog combinations that will show you all possible chainring/cog combinations with (nearly) the same gearing.
For example: At the Outdoor Retailer Winter show, I was talking to Jordan from Timbuk2. While he was in town for the show, he borrowed a bike from a friend to ride around on. It was a carbon Scott TT bike that had a broken rear derailleur hanger, so the owner converted it to a fixed gear. Unfortunately, due to the shape of the chainstays, he was not able to run a traditional chainring/cog setup, such as 42/15.
Using the Alternate Gearing calculator, you can see that a setup of 60/21 will give similar gear inches of 75.1 (42/15 gives you 73.6 gear inches)
One glaring negative about the program, is that it will not save your settings, so each time you go back into it you have to re-enter your preferences.
For a free app, it’s well worth it.