Bikes come with all sorts of drivetrains these days: triples, doubles, 1 by 11, singlespeeds and it can be difficult to figure out what kind of gearing is going to be best for your riding style, cycling strengths and terrain. Knowing a bit about gear ratios can help you determine what kind of drivetrain is best for you and your riding style. We have to warn you: there is math involved! But we are going to break it down to the basics and help you figure out what the numbers mean, so don't worry, you won't actually have to do any of the heavy lifting.
To determine how far a pedal stroke will take you plug in the following information into this formula:
Gear Development (ft) = ((# of Chainring Teeth/# of Cog Teeth) x Wheel Size (in) X 3.14) / 12
To figure out how fast a given gear ratio will go, you plug the number you just got into the following formula:
Speed (mph) = Gear Development (ft) x RPM x .0114
Ok - so that's a ton of formulas. Really to compare what a given gear ratio will give you just look at the gear ratio itself. The gear ratio is the number of teeth in the chainring divided by the number of teeth in the cog. And then just remember that those gear ratios are relative numbers and you can draw some conclusions about what ratios will be easier to pedal and what will be more difficult.
Anatomy of a Drivetrain
Cassette: This is the stack of cogs that acts as the bike's gearbox. The small sprockets provide higher gears (harder to pedal and pushes the bike farther per pedal stroke). Modern cassettes for both road and mountain bikes have 9, 10 or 11 gears.
Rear Derailleur: This is the little machine that pushes the chain up and down the rear cassette in connection with the shifters. It also takes up slack in the chain as the chain moves up and down the cassette.
Front Derailleur: Another little machine that pushes the chain on the chainrings in connection with the shifters.
Chainrings: These are the rings on the crankset. The larger the chainring the farther the bike will travel per pedal stroke (note this is opposite from the cassette). Most mountain and road bikes have two or three chainrings. New this year, SRAM has developed a drivetrain that only has one chainring (and doesn't have a front derailleur).
Chain: The chain is pulled around the chainrings and the cassette and transfers your pedaling energy into forward motion.
Shifter: These are the little machines on the handlebars that pull the cables to move the derailleurs and shift the bike.