Bike fit is the most important part of achieving a comfortable ride, and it starts with accurate measurements. A road bike frame is the first component to measure for, and it is also the most difficult. Although you might have accurate inseam numbers, you could find that a certain frame that matches your size does not feel comfortable, whereas a slightly smaller or larger bike fits perfectly. Use these measurements as initial guidelines when determining bike fit, but remember that nothing can substitute for test rides and trial and error.
Stand against a wall wearing your cycling gear, but without shoes. Place a ruler or book spine firmly at your crotch, simulating the pressure of a bike saddle. Have a friend measure the distance from the floor to the top of the book or ruler. This is your inseam length.
Calculate your frame size by reducing your inseam measurement by slightly more than 1/3. According to ColoradoCyclist.com, your frame size will be your inseam length multiplied by .65. Depending on how a frame is measured, you may need to increase the final measurement by 1 to 2 cm. Ask your salesperson if you are unsure of a specific frame’s geometry.
Set up saddle height and plumbline on a frame you are considering. If you have trouble dialing in your pedaling position, try a different frame size.
Check handlebar height and reach. Pedal on a trainer for a few minutes to get settled into a riding position. You should feel comfortably stretched out in the cockpit, with your elbows slightly bent when your hands are on the hoods. Your shoulders and chest should not ache, and your body’s weight should be evenly distributed across the saddle and handlebars. Have a friend stand to the side and sight a plumbline from your nose to the floor. The line should run 1 to 2 inches behind the handlebars. A simple stem change can solve problems with handlebar reach if your frame fits properly in Step 3.
Test-ride the bike. Be sure your pedaling and torso positions remain comfortable, and note any soreness in your hands, elbows or shoulders.