This is the device on the rear wheel that determines how many gears your bike has. Wipe it down with a cotton cloth every few weeks so you can shift smoothly.
Your bike chain has to be oiled about every 300 miles, more often if you ride in wet weather. Use a bike-specific lubricant, such as Phil Tenacious ($8, amazon.com) and drip on one drop at a time. When the chain has a thin coat, wipe off any excess oil.
To choose the right bike for your size, straddle the frame with your feet flat on the floor. For a road bike, there should be 1 to 2 inches between the top crossbar and your crotch. Allow more space — about the size of your palm (4 or 5 inches) — for a mountain or cruiser bike.
Some bikes, like cruisers, have just one gear, while others, such as road bikes, often have more than 25 for varying terrain. In low gears, the pedals are easy to turn; use these for riding uphill. In high gears, the pedals are harder to turn; use these for downhill. Click the right shifter as often as needed to fine-tune the gears, adjusting to minor changes in the road, such as dips and small hills. Click the left shifter once when you need to make a big difference in your resistance, such as tackling a monstrous hill.
There are two basic styles of handlebars: dropped (curved) and upright (horizontal). Setting your handlebars to the right height is key to preventing back, neck, and shoulder pain:
Road bike: One inch lower than the saddle
Mountain bike: Three inches lower than the saddle
Cruiser: One or two inches higher than the saddle
Most of the better bikes come without pedals so that you can choose between platform (the flat ones your childhood bike came with), cage (flat with straps that are secured over the tops of your feet), and clipless (similar to ski bindings in that they require specially designed shoes that lock into the pedals). Beginners and commuters who ride in stop-and-go traffic should start out with platforms; cage pedals can be dangerous because you can't release your foot easily. When you feel comfortable with your bike-handling skills, try going clipless.
This lock system secures the wheels to the frame. Flip them open to pop a wheel off when you have to repair a flat.
The width of your saddle, aka seat, should accommodate the width of your sit bones; one that measures between 130 and 150 millimeters works for most women. Even more important: seat height. While sitting on the saddle, move one pedal all the way down to the six o'clock position. Your other knee should be bent 25 to 30 degrees, for optimal comfort and power. If your knee is bent more than 30 degrees, raise the seat; if it's nearly extended, lower the seat, says Scott Holz, a fit specialist at Specialized Bicycles in Morgan Hill, California.
When the knobby parts of mountain-bike tires look worn down or you see threads of rubber on your road tires, it's time to replace them, usually about every 3,000 miles.
The "balloon," commonly called an inner tube, is a tube inside the tire that is filled with air. To figure out how much air you need, look for the psi (pounds per square inch), which is printed on the tire's sidewall. In general, a road bike should be filled to 100 psi, while a mountain bike should be filled to 40 psi for trail rides and 50 to 60 psi for pavement rides.
Originally published in FITNESS magazine, June 2009.