Correct bike fit can be a highly technical process. However the suggestions listed below are "rule of thumb" that will give the rider a very good fit.
Frame Size: The simplest way to measure correct frame size is to straddle the frame in your shoes. There should be 1-3" of clearance between the top tube and your crotch.
Level and center the seat: Start adjusting fit by placing the bicycle on a level surface and checking that the seat is level. A good way to check is to place a carpenter's level on top of the seat. If you don't have this tool, place a yardstick on top of the seat and compare the edge of the yardstick to a horizontal sight line, which you know to be level such as a windowsill or the top of a building. From there personal preference will determine if the nose is up or down. Generally the nose is slightly up for males and slightly down for females.
Adjust seat height: The seat-height adjustment usually requires a someone to help. Put on your shoes, mount your bike and have your helper hold your or place your bike in the doorway, get on and hold onto the doorjamb to support yourself.
You've found the optimum seat height when your legs are completely extended at the bottoms of the pedal strokes with your heels on the pedals (photo A). Now, when you're actually pedaling, you'll have the perfect bend in your knees (photo B).
Find fore/aft seat position: This adjustment requires a helper, too. Place bike on a level surface next to a wall or post so you can hold yourself upright. Get on and move your feet into the position with crank arms parallel to ground. The fore/aft seat adjustment is correct when a plumb line (any piece of string with a weight on the end) hanging from the bony protrusion just below your forward kneecap, bisects the pedal axle. Slide the saddle forward or backward to attain this position. Note that this will affect the "Handlebar Reach" adjustment.
Check handlebar height: Inspect bar height by standing your bike on a level surface and viewing it from the side comparing the height of the seat to the height of the bars. Normally the higher the bar the more weight on your rear end and the lower the more weight on your arms. Rule of thumb is 1-2" below saddle nose. Many riders believe that this position creates "back pain" and opt for the bars higher than the saddle. Comfort (and perceived comfort) is critical and bars should be adjusted for comfort first. Keep in mind that too high will result in seat pain from too much weight on saddle.
Check handlebar reach: If the bars are too close or too far away, the rider may experience neck, shoulder, back and hand pain. On most bikes, to change length, you must replace the stem. And stems come in a variety of types and diameters.
To check reach a simple method is to place your elbow on your saddle nose and extend your arm and fingers towards the handlebars. The tips of your fingers should touch your handlebars.
You can move your saddle forward and back a little to fine tune the reach. But too much movement will affect the relation of your knees over your cranks causing knee problems
Check handlebar size/width: There are lots of different handlebar sizes and shapes, however, and changing might fine-tune your fit providing additional comfort.
Check width first. For optimal control and efficiency, drop handlebars should be about the same width as your shoulders. These bars come in different widths. Flat-bar widths vary, too. If bars are too narrow you may constrict the flow of air into your lungs.
Troubleshooting Common Bike-Fit Problems
|You're always scooting forward on the seat.||Stem may be too long so you pull yourself forward as you ride; saddle nose may be tipped down too much; saddle to far back on rails.||Install a shorter stem; level saddle. Move saddle forward on rails.|
|Your're always scooting back on the seat.||Stem may be too short so you feel cramped and push yourself back; saddle nose may be tipped back; saddle may be too far forward on the rails.||Install a longer sterm: level the seat and center it on the rails; move your seat back.|
|Lower back hurts||Stem too low or too long; must strain back to reach bars; or seat may be too high, causing rocking when pedaling||Try raising the stem/handlebars; still hurts? Try shorter stem; check and adjust seat height.|
|Neck hurts||Stem too low; must crane neck to see||Raise the stem/bars|
|Hands hurt||Stem too low; too much weight on hands; saddle may be pointed too far down||Raise the stem/bars; level saddle; install shorter stem to put more weight on saddle|
|Front of knee hurts||Seat too low and/or too far forward, straining knees||Raise seat; may need to move seat further back as well|
|Back of knee hurts||Seat too high, over-extending leg||Lower seat|
|Rear End hurts||Too much weight on the seat; or not enough saddle time to break in "rear end"||Raise handlebar position; check seat height as it may be too high; install longer stem to put more weight on hands|