With numerous makes, models and types on the market, choosing the best bicycle for your needs can be a complicated process. Among the many factors to be considered is how well a bicycle frame suits your body type. Though not an exact science, the relation between your inseam length, height and the size of the bicycle frame can help you to determine the ideal frame size for your height.
Measuring Your Height
In order to help determine your ideal bicycle frame size, the people at bike information website eBicycles have provided guidelines for a variety of bicycle types. To ensure that your measured height matches these guidelines, you should measure your height by removing your shoes and standing with your back against a wall. Stand with your feet slightly less than shoulder-width apart, then have someone measure the length from the ground to the top of your head. This measurement is primarily used as a general guideline to help direct you to the most common bicycle frame size for your height.
Measuring Your Inseam
Your bicycle inseam is not the same as your pants or clothing inseam. To measure your bicycle inseam, remove your shoes and stand with your back against a wall. With your feet shoulder-width apart, hold a book with its spine firmly against your crotch. Next, have someone measure the distance from the floor to the spine of the book. This distance, along the inner side of your leg, is your bicycle inseam. Although height and inseam are related, the main determinant of your ideal road bike frame size is your bicycle inseam measurement.
Road Bikes
To reflect common practice and road cycling's international culture, the frame size measurements provided by eBicycles are in centimeters. These frames are measured from the center of the bottom bracket, or the point at which the pedals turn, to the top of the bicycle seat tube. Starting at an inseam of 25 inches, the ideal bicycle frame size is 43 cm. As a general guideline, add one centimeter for every 1/2 inch increase in bicycle inseam after 25 inches. Please note that there are three exceptions to this in the chart provided by eBicycles: a 47 cm frame size is ideal for both a 27-inch and 27.5-inch inseam, a 54 cm frame is ideal for inseams of 31 inches and 31.5 inches, and a 60 cm frame is ideal for inseams of both 34.5 inches and 35 inches.
Mountain Bikes
Unlike the convention for road bicycles, mountain bike center-to-top frame sizes are provided in inches to reflect the sport's North American roots. For inseams of 25 inches and 25.5 inches, a frame size of 13 inches is ideal. In general, each 1-inch increase in frame size above 13 inches is ideal for a 1.5-inch range of inseams. For example, a 16-inch mountain bike frame is recommended for inseams ranging from 29 inches to 30.5 inches, with inseams ranging from 30.5 inches to 32 inches associated with a 17-inch frame. Please note that the one exception to this trend is for an 18-inch frame, which is best suited for a range of inseams between 32 inches and 33 inches.
General Considerations
Though the guidelines provided by eBicycles take into account both your height and inseam length, you should not purchase a bicycle based solely on these recommendations. To help determine the best frame size for your bicycle, you should request a professional fitting from a bicycle shop. Whether or not a professional fitting is available, ensure that you test ride any bicycle before purchasing. While these recommendations are designed to help you narrow your choices, comfort and personal preference should take precedence over such general guidelines.
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