Bike Fitting Method
Fitting is interfacing a human body to a machine. The machine has good quality control, the cranks are the same length, a 10cm stem measures 10cm, the pedals travel in the same plane as the frame... Human quality control is dismal. Leg lengths aren't the same, the spine is never straight and hips, knees and ankles are all defective by design. Just to make matters worse, the human body changes over time. The real trick to bike fitting is to understand the ranges that the body can work within, and add a little wiggle room where the body meets the bike.
My bike fitting method has 3 basic steps:
1) Put the rider within their range of motion.
2) Teach the rider how to get their body weight on the pedals.
3) Deal with asymmetry.
- Within range of motion:
Every joint in the body has limits to it's range of motion. My hip has about 110 degrees of range on a good day. If I fold myself in half on a bike, I can exceed that range of motion, but the pedal still has to go over the top. That pushes my hip off the saddle with every pedal stroke, starting with back pain and causing problems up and down from there. Within the pedal stroke there are two common sticking points, 12:00 (top of the pedal stroke and greatest angle at the hip) and 5:00 (furthest point from the hip). If those two points aren't within range of motion, there's no point in moving on.
-Teaching the rider how to get their body weight on the pedals:
Bike fitting is part bike adjustment, part rider skill set. The rider's upper body is entirely forward of the saddle, the weight must be supported somewhere. Lots of people think this is core strength, it can't be. You would need to be somehow attached to your saddle to use core strength to support your weight. Either the weight is on your pedals, or you're trying to make a bridge between the saddle and handlebars using your spine and arms. When you walk you support your body weight on your feet, but the bike throws a monkey wrench into the works - the pedals turn! Your brain says "don't trust that!" and you do what you do when you're falling, you find the next solid object to catch yourself. That's why people put their body weight into their handlebars. If the rider can't support their body weight on the pedals, nothing you do with handlebar position will help.
-Dealing with asymmetry:
I could write a book on this subject and not even scratch the surface. The bike is the worst case for asymmetry. If you have a leg length discrepancy and you're walking, as soon as your foot leaves the ground it has freedom of movement, so you're self adjusting. Clip into a set of pedals and that self adjustment goes away. Dealing with asymmetry is a game of small adjustments at the points of contact to fool the body into thinking the bike is just as asymmetric. i will add that the bike industry is not well equipped to do this...