How to Size a Mountain Bicycle

By Gary Filippelli (1996)
Flip Flop Cycle Shop

The most important thing about sizing a mountain bicycle is that one decides on the kind of use intended, either road or off road or any combination of these. There are decisions on what percentages of time you will be using the bike for: commuting- pleasure road – off road – dirt road – training – etc.

In general, the more road riding you will be doing, the larger you will want to size the frame (frame sizes go from a small 10 in. to a very large 24 in.) on your bicycle. The more off road or trail riding, the smaller you will want to size the frame.

It is helpful to know how tall you are. Have a friend help you with the next measurement which we will call “standover height.” Stand against the wall with the phone book or other book square against the wall and up to your crotch comfortably and measure this standover height. In general, for off road riding, you will need this height. For men-subtract four inches from this height, and for women – six inches. This is the standover height you will be looking for on the bicycle frame. For more leisurely riding, also known as road riding, subtract only one or two inches from your standover height to get the right frame or bike standover height that fits you.

Next, we will size the stem. The stem is the part of the bike that holds the handle bars. By sizing the stem, we will put the handle bars in the correct position in relation to your seating on the bike to optimize your control.

Pick a spot on the floor and make believe it’s a bug. Now stomp on it, grind it into the ground. Notice how the joint of your knee is positioned above the ball of your foot. Now think of the pedal axle as the ball of your foot when your pedals are at three and nine o’clock while you are seated on the bike. The length of your thigh measured from your knee to your seat bones will determine where your seat will be positioned on the seat post by sliding the seat on its rails. Once this is done, you can pick the length, angle or rise of the stem to put you in the riding position that best suits your needs.

One needs to choose a position that makes you feel comfortable and in control of the bicycle for your particular use. For a more aggressive rider, you would need a lower angle and a longer length. However, for a slower, and a more leisure ride, one will need a larger angle and a shorter length.

Because mountain bikes are built with more consideration and thought for comfort, dependability, and ridability on various surfaces, it is suggested that one takes the time to ask the right questions and to be fitted for the bike that is just right for the rider.