Proper bike fit: Highlights from the Clinic at Summit Chiropractic and Rehabilitation: Part 1
Many thanks to all who attended last nights event. Yes, the feet propel the bicycle and foot and lower extremity biomechanics can make the difference between agony and ecstasy, or winning and losing.
Proper bike fit can make a huge difference in your performance, endurance, and enjoyment, as well as help prevent injuries. There are several key factors to remember when fitting your bicycle: frame size, saddle height, saddle fore/aft position, handlebar height and width and handle bar reach. We will discuss each in turn and talk about some of the ramifications of improper adjustments.
Frame size: People often buy frames that are too large for them.This creates a multiplicity of problems, from lower back pain to knee pain due to the constant motion back and fourth or hyperextension of the knee.
Frame size refers to the length of the frames seat tube. It can be measured 2 ways: 1) center to top (from the center of the bottom bracket (ie center of the pedal spindle) to the top of the top tube or seat post) and 2) center to center (from the center of the bottom bracket to the center of the top tube. The former is a larger measurement; usually by about 1-1.5 cm. C-T measurement for a road frame is .67 X inseam length. C-C measurement for a road frame is .65 X inseam length. Larger riders may find this size too small, so they usually pick a length 27-28cm less than their inseam (this will give you a larger number than the previous method).
Mountain biking is much more dynamic, with the rider in almost constant up and down/ side to side motion. For reasons beknownst to many, mountain bikers often need more “clearance” over the top tube. They should select a frame 10-12 cm smaller than a road frame.
Many bikes have different geometries, so there often is a compromise between top tube height and frame length. This is especially true of women’s specific frames. Women often have longer leg to torso ratios, so the rear triangle and top tube lengths are different to put their knee over the pedal axis.
Saddle/seat height: Cyrille Guimard, a French team manager who has coached many Tour de France champions in last 20 years, developed a formula which I feel is the simplest and often the best: measure the inseam from your perineum (the very bottom of your pelvis, between where the thighs meet the torso) straight down to the floor (not along the legs) while standing barefoot, and feet comfortably, about shoulder width apart. Multiply this number by .883. This will be the saddle height, from the center of the bottom bracket (where the cranks meet the frame), along the seat tube to the top of your seat. This measurement is usually reliable within 1 percent of the mark.
Another method is to measure the bend in the knee with the foot clipped in and held flat (toe NOT pointed) at bottom dead center (crank even with the angle of the seat post). It should be between 20-30 degrees. This is a more aggressive measurement that often results in a higher seat than the previous measurement.
If your saddle is too high, it can cause:
1. A rapid decrease in power output from the quadriceps and gluteal muscles, making it more difficult to pedal
2. Stress on the knees due to being fully extended and locked on your down stroke.
3. Pelvic rocking, which can create lower back pain
If your saddle is too low, it can cause:
1. A more gradual decrease in power output, making it harder to pedal to because of the mechanical disadvantage of the thigh and buttock muscles.
2. Compressive forces on the top of the kneecap at the beginning of the down stroke can cause knee pain, especially when climbing hills. This will be exacerbated if you pronate.
3. More stress on the lower back because of excessive bending at the waist to reach the handlebars (from the more horizontal angle of the hips and reflex tightening of the hip flexors).
Bike Fit. The Gait Guys. Yup, we do that too
