According to the United States Environmental Protection Agency, fossil fuel use for the purpose of transportation results in one-third of carbon dioxide emissions in the country. Of that number, nearly 60 percent of the carbon dioxide came from personal vehicles (See Reference 1). For a green alternative, riding a bicycle to run errands or commute to work emits no carbon dioxide or other greenhouse gases, but the wrong size bike can cause problems. If you’ve been avoiding getting on your road bike because of shoulder or neck discomfort, you may have a stem that isn’t fit correctly to your body. With a few measurements, you’ll know what size stem you need to make riding your bike comfortable and efficient.
Stand in bare feet on a solid floor, not carpeting, with your feet 2 inches apart. Measure your inseam by taking the tape measure straight down from your groin to the floor. Record this number.
Measure your body length by measuring straight down from the notch just below your throat (known as the sternal notch) to the floor. If your belly protrudes enough to disrupt a straight line, hold a pencil horizontal to your sternal notch and measure straight down to the floor. Record this number.
Subtract your inseam length from your body length. This number is your torso length. Record this number.
Measure your arm length by holding your arm out, elbow straight, at a 45-degree angle from your side. Measure from the large bone at the outside of your wrist to the spot where your shoulder joint begins.
Add your torso length to your arm length to get your arm-plus-torso length. Record this number.
Determine your riding style. If you use your bike to run errands or commute to work and like to take it easy while riding, consider yourself a casual rider. If you want to do sprints or race your road bike, consider yourself an aggressive rider. If you’re somewhere in between, consider yourself a mid-range rider.
Multiply your arm-plus-torso length by the factor for your riding style to find your ideal stem length in centimeters. If you’re a casual rider, this number is 0.09; if you’re a mid-range rider, use 0.10. Aggressive riders will multiply by 0.11.
Multiply your ideal stem length by 100 to change centimeters to millimeters. Most bike stems are measured in millimeters, not centimeters.