Bicycle Sizing Information - page two
How To Adjust Your Saddle Height
When you have determined the correct frame size, the saddle height can then be set. This measurement is determined from the center of the bottom bracket to the low point of the top of the saddle. To set this, multiply your inseam by .883 and use the result for your saddle height. This will allow you to fully extend your leg while pedaling, with a slight knee bend at the bottom of the stroke. This height will be something that you adjust slightly as you adapt to the position, depending on the type of pedals you use, and the position of your feet as you ride.
Finding Your Neutral Knee Position
To achieve neutral knee position, put your bike on a stationary trainer, leveling out the bike by raising the front wheelterm. Have your helper check your position, or use a video camera or mirrors to check this yourself. Position the ball of you foot directly over the pedal axle, in a natural position. Warm up for about 10 minutes. Slowly stop pedaling while looking ahead, and bring the pedals to a stop with the cranks parallel to the floor. The goal is to have your forward knee directly above the center of the pedal spindle and the ball of our foot. Move your saddle forward or back to adjust for this position. Be aware, that if you need to adjust the saddle position, you should be sure to recheck the height, as well, since the fore/aft position affects the height of the saddle.
Determining Top Tube and Stem Length
The horizontal fit of the bike will give you easier breathing, spinal comfort and appropriate weight distribution, which in turn, equates to better bike handling.
The horizontal fit is the most variable of positions. This depends on physical fitness levels, body proportions, riding style and more. Additionally, your position will change with riding experience. The goal of this aspect of bicycle fitting is to get your back in a low and long position. It may be difficult to achieve a truly flat back, but a cyclist should aim for a longer position over the bike.
All that said, there is not a formula that will establish this with the relative accuracy found with the inseam method. The best way to find a starting point is to look at your current bike and see how you would like to change the horizontal fit. To do this, measure your old bike's top tube, and add to this the measurement of the stem. Stems can be purchased in incremental sizes to help you achieve your best fit.
Other Sizing Issues
There are a number of other sizing issues that you can consider, such as handlebar size, cranks and gearing. These are covered, along with more detail about custom bicycle sizing, in an excellent article posted at the site of our sponsor, titled, "How To Fit Your Custom Bicycle".