Proper bike fit leads to better performance, comfort
With springtime here and the snow melted, folks are thinking about biking. 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: People often buy frames that are too large for them. This creates a wealth 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 two ways: 1) center to top (from the center of the bottom bracket – 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 centimeters. C-T measurement for a road frame is .67 times the inseam length. C-C measurement for a road frame is .65 times the inseam length. Larger riders may find this size too small, so they usually pick a length 27-28 cm 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. 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-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 the 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 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 or low, it can cause injuries and a decrease in power.Saddle/seat fore/aft position: There are two ways to make this measurement:
1) When your legs are at 90 degrees in your power stroke (cranks are horizontal), drop a plumb line from the tibial tuberosity (the bump on the leg just below the kneecap, where your quadriceps attaches). This line should intersect the pedal axis or be slightly behind it.2) If you like to ride with the seat a little back, drop the plumb line from the front of the kneecap. It should intersect or fall slightly behind the pedal axis.The a general rule of thumb is that cyclists in spinning classes, or those who like to push lower gears, tend to sit slightly forward. Those who push higher gears and spin slower, sit a little further back.If your seat is too far back it can cause lower back pain because of the increased flexion occurring in the trunk. Cyclists will often feel pain just below the waist where the gluteal muscles attach or in the middle of the lower back, where the hip flexors attach. If the seat is too far forward, cyclists usually experience knee pain.Handlebar Height and Width: Handlebars should be approximately shoulder width and be 0-2 inches below saddle height. The wider they are, the more they open up your chest and allow better breathing, but this is at the expense of aerodynamics. The higher they are, the less stress on your back and neck.
With your hands in your most common riding position (on the grips, hoods or in the drops) you should be able to look down at the center of the stem/handlebar intersection and not be able to see the front axle. If the bar is in front, you may have trouble with descents; if behind, you way be doing wheelies uphill! Problems can often be remedied with a change of stem with a different length, pitch or both.Crank Length: There are no hard and fast rules here. This often depends on individual preference. Long cranks are great for leverage and offer advantages for climbing and big gears. Shorter cranks are better for spinning. As a starting point, 54 cm and smaller road frames should use 166-170 mm; for 55-61 cm road frames, 170-172.5 mm cranks; frames 62 cm and larger, 175 mm. Mountain bikes generally use longer cranks to generate more torque and are often 175 mm. Test drive these adjustments/measurements and watch your improvement in both performance and riding comfort. Less experienced cyclists should make small adjustments at first, allowing time to accommodate to the new fit. Remember, efficiency and injury prevention are key to maximize riding time.Dr. Waerlop enjoys cycling and works with and on many local bikers. He performs bike fits and video pedal stroke analyses. He practices at Summit Chiropractic and Rehabilitation, located at 129 West 10th Street (behind Grease Monkey) in Silverthorne. He can be reached at (970) 513-9234.
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