How to Size a Bicycle Frame

Properly fitting a bicycle frame to its rider is a key component for cycling enjoyment. If the bike is too big or too small in proportion to your own body measurements, you are at risk for crashing, difficulty in riding and possible injury. While knowing your measurements is helpful in sizing a frame, ride the bicycle before purchase to ensure that the size and geometry work for your riding style.

Things You'll Need

  • Measuring tape
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Instructions

  1. Finding Your Size for a Bicycle

    • 1

      Record your body measurements. You will need your height and your bicycling inseam. To measure your height, stand in bare feet with your heels backed against a wall. Have someone make a mark at the top of your head and measure this length. A cycling inseam is slightly shorter than the measurement used to fit trousers. Stand in bare feet with your legs spread about shoulder width. Measure from the bottom of your crotch to the floor.

    • 2

      Determine the seat tube length on the bicycle you are interested in. The size marked on a bicycle frame is keyed to this measurement. A 17-inch size indicates that the seat tube is 17 inches in length from the bottom bracket where the pedals are installed to the top of the tube that intersects with the seat tube. As a rough estimate, you want to be able to safely stand over the top tube with a couple of inches to spare between the tube and your crotch area. Mountain bike riders generally want more space given the rough terrain in which the bicycle is operated.

    • 3

      Determine the top tube length. The top tube connects the seat tube and the fork bracket, and the length of this tube will determine how upright or bent-over your riding position will be. In order to maintain the geometry of their designs, the bike manufacturer will match a longer top tube with a taller seat tub assuming that a longer inseam means a taller rider. Test the riding position to ensure it is comfortable for your height and the proportion of your torso to leg length. Much can be done to adjust the fit of this measurement with adjustments to the saddle height, the bar rise and headset, and the crank length to ensure a comfortable ride.