Get the Bike Frame Size Correct Before You Do Anything Else

If you had never seen a bicycle before it might be hard to imagine it as a fast, efficient, comfortable means of transportation. By careful consideration when selecting a bike, all three of these results can be realized.

One of the most important issues to address when choosing a bike is the size of the bike. Bike sizes generally do not correspond to age or experience of the rider, but rather to the height and leg length.

Usually the frame sizes are given on seat tube length and most manufacturers measure from the center of the crank axle to the center of the seat tube where it joins the top tube. Always check how measurements are done – some bikes are measured from the center of the crank axle to top of the seat tube, which can make a big difference.

When you go to buy a bike you will find that for ease of general classification, tire sizes are used as the most common point of reference, but it is the frame size that determines which bike is the best fit for you.

The first important measurement to be aware of is called the “stand-over height”. Begin by measuring your inseam, that is, from the floor to your crotch. Now, depending on which type of bike you will be riding, the stand-over height will vary.

For a mountain bike, it is recommended that you add 3” – 5” to your inseam length to determine the appropriate stand-over height. If you anticipate being a very active rider that spends a lot of time riding on very bumpy and rough terrain you might want to lean more towards a longer stand-over height to give yourself more clearance between the bike’s top tube and your crotch.

To help make the selection process a little more efficient, so that you don’t have to have to stand over every bike in the store to determine if it meets these requirements you can narrow down your selection by determining beforehand, which frame size will give you the appropriate stand-over height. Since, a bike's frame is measured from the center of the cranks to the top tube, you can find your recommended frame size for a mountain bike by multiplying your inseam measurement by 0.59. This means that it you have a 34-inch inseam (34 x .59 = 20.06) would probably want a bike with a 20-inch frame, depending on the available sizing options.

Road bikes are typically used on smoother surfaces than mountain bikes so the difference between inseam length and stand-over height can be less. The manufacturers of road bikes usually list the frame sizes in centimeters rather than inches. Simply multiply your inseam length in inches by 2.54 to convert the length to centimeters. It is generally recommended that the stand-over height is 5 to 9 cm longer than the inseam length. Multiplying your inseam, in centimeters, by 0.65 will give you the suggested frame size.

Once you have the frame size correct it is easy to adjust the seat and handle bar heights to fit you perfectly. Every cyclist eventually comes to appreciate the advantages of a properly sized bike. A bike that fits makes it possible to ride longer, farther, and faster which all lead to a more enjoyable cycling experience.