Comfortable: Being comfortable doesn’t mean being in a slow position. It means using your certain body structures to support the position desired. If you cannot hold the triathlon position then there is very little to justify getting a tri specific bike.
Arm Angle: Below is a picture of the how the weight of your upper body should be supported. By using your bone structure to support yourself you can let the muscles relax and therefore be comfortable. Body landmarks being used are the acromion process, center of the elbow, and then following the center line of the forearm. The angle should be around 85-95 degrees. If you are at a bigger angle (over 110 degrees) the muscles are forced in tension to support the upper body, this in turn causes discomfort.
Saddle Height: By measuring from the greater trochanter to the knee center to the lateral maleolus. The pedal stroke should follow the line from the pedal-bottom bracket-center of the saddle. This generally puts the pedal stroke at about 6:25-6:30. The angle one wants to achieve is somewhere between 143-155 degrees. Generally if you saddle is too high you will experience pain in the back of you knee due to an overstretch of the hamstrings.
Hip Angle: This is measured by drawing a line through the midline of the torso and another line from the center of the bottom bracket going though the greater trochanter. The hip angle will fall between 95-105 degrees. If this angle is too small as you will find with people that ride a road bike with aerobars there is a loss of power and the overstretching causes lower back pain.
So ends this first lesson in tri bike fitting. I will go deeper into this subject in future posts.