Andy Pruitt: Bike Fit

Andy Pruitt needs no introduction to RBR roadies. The director of the Boulder Center for Sports Medicine and author of the eBook, Andy Pruitt’s Medical Guide for Cyclists, Pruitt has worked with world-class riders for 30 years in Boulder, Colorado. He’s also an accomplished cyclist himself.

• Modern bike fit comes from the parameters addressed in Italy’s Central Sports School Manual (C.O.N.I.) in 1972. It detailed frame size and fitting calculated from body segment averages of Italian racers. These were static formulas used for measuring a rider while he sat stationary on his bike. They worked fine as long as you were Italian, young, lean, male and of national-team caliber. But for most of us, they don’t work very well at all.
• Static fit formulas assume that everyone’s anatomy is the same. But of course That’s not true. For example, we’re told that we should place the knee directly over the pedal spindle (axle). Bike fitters use a plumb line dropped from the kneecap while the rider sits on the bike on a trainer. The line’s relationship to the end of the crankarm is used to determine the ideal saddle fore/aft position.

  However, the end of the femur is elliptical, shaped like a football, and this shape changes the location of the knee’s center of rotation. A stationary measurement doesn’t always accurately correspond to a rider who is actually pedaling.

• The human foot is made for walking, not for pedaling. It acts like a spring in the walking or running gait, collapsing as it hits the ground and then returning that energy when you spring forward. Think of the foot as a leaf spring during walking, storing and returning energy. But in cycling we need a rigid foot. That’s why cycling shoes have stiff soles.

  A shoe in men’s size 9 is the midpoint of the range. Usually, a size 9 shoe should have the cleat mounted so the pedal axle is directly under the ball of the foot (the “neutral” position). But larger feet want stability. If you wear larger than a size 9, generally you should move the cleat toward the rear of the shoe sole. Conversely, smaller feet want more leverage for the pedal stroke. If you wear smaller than size 9, consider sliding the cleat slightly forward from the neutral position.

• If you need orthotics (custom insoles), be sure they’re cycling specific. Those made for running won’t work because They’re “rear posted” for heel-strike activities. Cycling is a forefoot activity, so cycling orthotics should be posted from the ball of the foot. While running orthotics generally extend only from the heel to the front of the arch, cycling orthotics extend at least to the base of the toes. In many cases They’re as long as your foot.