You'll have a more comfortable ride when your bike stem, which attaches your handlebars to the bicycle fork on your frame, is of the correct length for your size and riding technique. The stem length is important because it helps put you in a riding position where your body weight is more appropriately distributed, thus preventing soreness and tightness in the neck, back, hands and shoulders.
Determining Stem Length
Because correct stem length is dependent on your particular size and your riding technique, the best way to determine the ideal length is to sit on your bike and find where you’re most comfortable. Bike stems are available in multiple lengths, typically ranging from 90 to 130 millimeters. A bicycle shop employee can help you find the best stem length, but with a partner you can also do this at home. Sit on your bike and hold your handlebars that have not yet been attached to your bike frame. Lean forward into your comfortable drop position, with your torso tilted and arms held out like when you're riding; have a partner help support the bar in the air if necessary. Make sure your back is flat, your shoulders aren’t hunched and your arms are slightly bent. Maintain the position while your partner makes a horizontal measurement from the center of your bike frame to the center of the handlebars. This measurement is what you will use to select the appropriate stem length.