Sizing Up the Frame

Frame size is the most important consideration when fitting a bike. Unlike most other factors, the frame is one thing you can’t modify. If you end up with a bike that has a frame too small or too large, you won’t be able to adjust the saddle and handlebars enough to compensate for the improper dimensions. Plus, an incorrectly sized frame can be dangerous, making start­ing, stopping, and handling more difficult.

When you’re shopping for a new bike or frame, let the staff at your local bike shop assist you. They have experience matching customers to bikes, and they understand the different factors that come into play when choosing a frame.

The bike-shop staff will want your inseam size. This is the length from the floor to the top of your crotch. They’ll take this number and subtract 10 to 12 inches from it, based on how tall you are, which will give them an estimation of the frame size you need. Remember: This is just an estimation — every bicycle will fit a little differently, depending on the manufacturer, model, type of bicycle, your riding style, and so on.

Frames are generally measured from the center of the bottom bracket to the top of the seat tube (see Figure 19-3), although manufacturers have different variations of this measurement. After the bike-shop staff has a general idea of the frame size, they’ll have you try out various bikes with this size. To con­firm the size, they’ll have you straddle the bike with both feet on the ground and the frame between your legs. In this position, there should be at least an inch or two of space between the top tube and your crotch, more if it’s a mountain bike.

Figure 19-3: How frame size is measured.