cycle performance: how to properly fit your bicycle

Bicycle Position Overuse injuries in bicycling often result from either improper bicycling position or the lack of sufficient time for adaptation to a new position. Proper bi­cycle position and sufficient time for adaptation to a new position help prevent many injuries. 

Certain general principles apply. There is a "window" of perfectly accept­able bike fit. The final decision regarding a position must be made by the individual rider. Bicycle position is a compromise among many bicycling needs. Optimal position is different for maximizing muscle power, aerobic efficiency, and com­fort and for minimizing injury. Too often, riders are "classically" positioned without regard for their individual variations. Riders with anatomical variants-for example, upper or lower extremity discrepancy, or turned-in or turned-out feet-should be fitted to allow for these differences.

GETTING STARTED

EQUIPMENT

Bicycle, stationary trainer, bike tools, plumb line, level, tape measure, calipers, assistant.

LEVEL BIKE

Set the bicycle on a trainer. Use blocks of wood to raise the front of the trainer to level the bicycle if necessary. Have the seat in a horizontal position to start.

WARMUP

Pedal moderately for at least 10 minutes before adjusting. Pedal moderately for a few minutes between adjustments.

PROPER FIT CHECK LIST

The order in which you perform adjustments is important-some measurements are dependent upon others. The order suggested here works best for most riders.

Frame Sizing

For road bikes, measure the inseam and multiply by 65%. This number is a starting point for the frame size you will need. Find the inseam measurement by standing with back to the wall and a 1-inch book binding snug up against the crotch. Measure the distance from the floor to the top of the binding.

Pedal Fore-Aft

The cleat should be positioned so that the ball of the foot is over the pedal spindle. Sprinters may prefer to back their feet out of the pedals a little more and to be more on their toes.

Seat Height-Paramount in Importance

Seat height selection is a compromise between aerobic efficiency, aerodynamics, power, and injury reduction. Cleat thickness, pedal type, and seat tube angle all influence this measurement. Formulas based upon inseam measurements or other body dimensions can only give approximate results and can only provide starting points.

The general idea is that the higher the saddle, the more power you can generate and the less the aerobic cost. You must not be so far extended that your hips rock or that your spin is restricted when you pedal. Some riders determine position by raising the seat until their heels can just clear the pedals. A seat height that results in 25 to 30 degrees of the knee flex ion when the pedal is at the bottom of the stroke tends to result in the least injury but is not optimal for cy­cling power or aerobic efficiency.

The higher your seat, the more likely you are to have pain in the back of your knee, Achilles tendon pain, or buttock ache. Those with limited flexibility are the most likely to have problems. Further discussion about seat height is found in the chapter "Optimal Seat Height.”

Seat Position Fore-Aft

Some riders position the seat fore-aft by measuring the distance that a plumb line, hanging from the nose of the saddle, falls behind the bottom bracket. Road riders tend to place the seat an inch or more back. Sprinters and time trial riders tend to use a more forward position. Other riders determine their seat position by dropping a plumb line from the front of their knees when the cranks are horizontal. They look for the plumb to fall through the pedal axle. For most standard bicycles, road riders usually have their seats all the way back on the rails, time trialists all the way forward, and crit riders in between.

After you have adjusted the fore-aft position, repeat the determination of your seat height, since adjustment of the saddle fore-aft may change the seat height.

Seat Angle

Most riders ride best when the seat is level. Sprinters, aero time trialists, and women may prefer to have the noses of their saddles point down slightly. Climbers may prefer to have the noses point up slightly.

Pedal Rotation Angle

The cleat should be positioned so that your toes point nearly straight ahead. Some riders prefer their feet pointed slightly in, some slightly out. You may wish to ride a little with your cleats slightly loose, and see where you are most comfortable before the final tightening. Cleat position is not as critical with free-rotation systems. In general, if the outside of your knee hurts, adjust your cleats to point your toes a little more outward. If the inside of your knee hurts, point your toes a little more inward.

Stem Height

The stem may be from one to three inches below the height of your saddle. The lower the stem, the more aerodynamic you'll be. If the stem is too low, you may be uncomfortable, especially in your lower back, or you may lose power.

Stem Extension

Most bikes are sized so that most men end up needing stems 10 to 13 centimeters and most women require stems several centimeters shorter. When you are in the drop position, there should be scant clearance between your elbows and your knees, and your back should be flat. A rule of thumb is that the top of the bars should obscure the front axle when you are looking down with your hands in the drops.

Mountain bikers often prefer a combination of longer top tube and shorter stem for better handling on cross-country trails and down hills.

Handlebar Shape

The shape of the handlebar varies with the type of riding. For general road rid­ing, a long top horizontal section is preferred for climbing comfort. The drop of handlebars is partially determined by the comfort level of your hands in the curve.

Handlebar Width

The handlebar width should be roughly the width of your shoulders.

Handlebar Angle

The handlebars should be angled so that the drops are perpendicular to your seat tube. This means that they are pointed down about 15 degrees.

Brake Levers

The brake levers are most comfortable when they are so positioned that their tips are in line with the bottom of the handlebar drops.

Toe Clips and Straps

If you use them, make sure that there is a small clearance between the tip of your shoes and the clip. Make sure the toe straps are at the outside edge of your shoes.

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