To build an app you need a simple concept and an audience.  I figure(s) the best audience to address, initially, is (I think you can guess and what better place to start?) el Mundial de Los Freddies.

I’m gonna get some base miles with an application that addresses everyone’s favorite topic during single speed season:  The Gear Inch Calculator {and other related metrics}.  There are plenty of gear inch calculators but it’s a simple application to break the app ice and the audience is well defined.  To get started we need a couple of simple equations by which all the other metrics can be derived.

Gear inches vs. Meters of Development and the case of 81

Gear inches is a system that assigns a measurement to gear ratios and is not the distance your bicycle moves forward with each complete pedal stroke.  The distance forward is referred to as Meters of Development.

Chain Ring / Cog Dynamic: If you have a chain ring and rear cog with the same number of teeth, one chain ring revolution will turn the wheel one complete revolution.  If the chain ring has twice the number of teeth, then one revolution of the pedals will turn the wheel two complete revolutions.

Gear Inches:   gear inches = dia • (t1/t2)

dia = diameter of the drive wheel (rear wheel)
t1 = no. of teeth on the chain ring
t2 = no. of teeth on the rear cog

Meters of Development:  md = cir • (t1/t2)  =  π • dia • (t1/t2)

cir = circumference of the drive wheel (rear wheel) {π • dia}
t1 = no. of teeth on the chain ring
t2 = no. of teeth on the rear cog

Still reading??  Wake-Up !!

81:  Typically, for 700c wheels (nominal* diameter=27inch), you get an 81 inch gear with a chain-ring/rear-cog ratio of 3 to 1:  81 = 27•(39/13) {39 tooth chain ring and a 13 tooth cog} or 48/16.

You can see the difference between a gear inch and meters of development is π (pi ~3.1415962 / circumference =  π • diameter).

It’s also apparent, by the equations,  that the concept of a “bigger gear” (relative to a specific chain-ring) is inversely proportional to the number of teeth on the rear cog.  When you hear Freddie say  “Put it in a bigger gear” you’ll understand it to mean; put the chain onto a smaller cog {or put it in the big chain ring}, i.e., put it into a gear that gives you more inches. More Inches = Bigger Gear.

*nominal: of, being, or relating to a designated or theoretical size that may vary from the actual : approximate

Visit Wikipedia if you’d like to read more about Gear Inches & Meters of Development.

Some very good web-based gear charts:
1) www.correal.net/gearcalc.htm
2) www.machars.net/bikecalc.htm

3.1415 Animaux!