How to Determine the Frame Size of a Road Bike

Determining the correct fit is important when considering the purchase of a new road bike. Accessories and paint will mean nothing if the bike is not properly sized to you. A frame that is too small or too large will result in an uncomfortable ride. Choosing a bike correctly sized to you involves taking measurements of your body and matching the results to a frame size that will provide a good fit.

Instructions

Difficulty: Moderately Easy

Things You’ll Need:

Tape measure
Paperback book
Pencil

Step 1

Measure your inseam using a tape measure and a paperback book. Remove your shoes and position yourself against a wall. Place the paperback book between your thighs with the spine of the book as high as comfortably possible.

Step 2

Mark the wall at the top of the book edge using a pencil. Use a tape measure to obtain your inseam length by measuring from the floor to the marked point on the wall. Remember that the size of the frame is referring to the length of the seat tube on the frame of the bike.

Step 3

Convert the measurement for a bike measured center to top or center to center. The center to top method is determined by measuring the bike from the midpoint of the bottom bracket to the top of the seat. The center to center method is determined by measuring from the midpoint of the bottom bracket to the midpoint of the top tube.

Step 4

Determine the correct frame size for bikes measured center to top by multiplying your inseam by 0.67. If your inseam is 31 inches, this would result in a correct frame size of 21 inches (31 x .67 = 20.77 or 21-inch frame). Round the total up to the nearest whole number.

Step 5

Multiply your inseam by 0.65 to determine the correct frame size for bikes measured center to center. If your inseam is 31 inches, the correct bike frame would be 20 inches (31 x .65 = 20.15 or 20-inch frame). Round the total down to the nearest whole number.

Tips & Warnings

Test the bike before purchasing to make sure the bike fits you especially in regard to the top tube.

Article Written By Keith Dooley

Keith Dooley has a degree in outdoor education and sports management. He has worked as an assistant athletic director, head coach and assistant coach in various sports including football, softball and golf. Dooley has worked for various websites in the past, contributing instructional articles on a wide variety of topics.

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