While you used to be able to measure a bike frame in seconds, bicycle writer Sheldon Brown of Harris Cyclery in West Newton, Massachusetts, notes that "nobody knows how to measure a bicycle's seat tube any more." You'll need to deal with what Brown calls "anarchy" in bike frame measurements by following a logical approach to arrive at the correct size.
Step 1
Look for a label on the seat tube, typically on the front edge above the cranks. See whether it lists a figure in centimeters for road bikes, typically from 43cm to 66cm, or in inches for mountain bikes, typically 14 inches to 22 inches.
Step 2
If no label is present, measure from the center of the crank to the top of the seat tube using a metal measuring tape. Multiply the inch count by 2.54 to come up with the frame size in centimeters.
Step 3
Measure from the center of the crank to the midpoint of the joint between the top tube and the seat tube because some manufacturers use this less common measure. Multiply this inch count by 2.54 to come up with the measure in centimeters.
Step 4
Compare your results for both measurements to the specifications provided online by the manufacturer. For example, if you have a Schwinn Sierra, double-check your measurements at SchwinnBike.com on the product page's "geometry" specifications, which lists frame sizes of 15-1/2 inches or small, 18 inches or medium, 20-1/2 inches or large and 23 inches for extra large. Round your measurement to the nearest official manufacturer's specification.
Things You'll Need
- Tape measure
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