Step 1: Level and Center the Seat
I also use a carpenter's level to adjust the seat angle. I place one end over the highest part of the right or left rear side and the other over the seat nose (i.e., in line with the rails under the seat as shown in figure 1
). Most individuals will do fine when you level the seat is level with the ground. However, if you notice numbness in the hands, you may be tilted to far forward and may need to tilt the seat back just a fraction (very small amount). If you notice numbness in the groin area, the seat may be tilted to far back. The correct angle will increase bicycle comfort.
Step 2: Adjust Seat Height
As shown in figure 2B
, when the leg is fully extended, there should be a slight bend in the knee. If there is not enough bend in the knee when fully extended, there is a tendency for one's hips to rock from side to side while cycling and this may result in knee pain (figure 2A
). Have a friend watch you while you cycle to advise you on these factors. Incorrect height can lead to knee pain as explained by Kirsten Gleason
on bike fit. The correct height will increase bicycle efficiency.
Step 3: Fore/aft Seat Position
Seat position (fore/aft) is another factor in bike fit. Two methods have been used, KOPS and CG (figure 3
). The Performance Cycle video
indicates that when the foot is in a "horizontal" position as shown in figure 4
, a plumb dropped in front of the knee cap should fall directly through the center of the pedal (so called "KOPS
" or knee over pedal spindle). This, however, is probably a myth as explained by John Crook of Crooks Cycle Right
. Although KOPS may be a good starting point for bike fit, the key is to have the center of your body mass approximately cm in front of the bottom bracket as shown in figure 5
There are many ways to figure out your "Center of Gravity" (CG
) on a bike, some using 2 scales, a phone book and angle measurement. The easiest is that described Keith Bontager
who also gives the best description of overall bike fitting:
"Then I determine the rider's CG (center of gravity). For convenience, I use his seated CG which I measure by placing the rider in a full crouch (with his rear end) against the wall (in his socks without his shoes on) and have him back on his feet a bit at a time until he is on the verge of toppling over. Since a human being always balances on his feet. I know his CG will be right over the balls of his feet at the moment he topples over.
I measure this distance away from the wall. This becomes the horizontal coordinates for the rider's center of gravity."
One can also observe where the balls of his feet are in relationship to his navel. The balls of my feet are approximately 4 inches above my navel in the crouched position. This is the point (center of gravity) one desire to have lined up about cm in front of my bottom bracket.
You can later try moving the seat fore or aft to get a better bike fit. Some sprinters rather be slightly forward and some recreational rides rather be slightly aft of this position. It is a mater of choice and comfort.