t t h s d s d h Fitting the road bicycle: a proportional approach

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1 Fitting the road bicycle: a proportional approach BY CHARLES HOWE No single position definitively maximizes power generation for any given individual, which is why there has never been a controlled, peer-review study demonstrating as much; rather, cycling economy the ratio of mechanical power output to oxygen uptake is largely determined by the percentage of Type I (slow-twitch) fibers present within the working muscles, although muscles are adaptive, and will, in a relatively short time, become marginally more efficient for any position within a given range of movement. Even so, bicycle fit can clearly be optimized for overall riding comfort and to minimize aerodynamic drag. The sort of proportional method described here does have its detractors; see, for instance, the excellent site (formerly In all likelihood, factors such as flexibility (which can increase over the course of a season, or be lost due to aging, injury, or inactivity), riding style (e.g., touring, recreation, competition), aerodynamics, and comfort will all modify the guidelines that result from the following procedure, so keep in mind that they are just that guidelines which should not be taken rigidly, as any sort of final word, but as a starting point that gets you in the ballpark, subject to further adjustment, such as from an old-fashioned, low-tech visual inspection by an experienced eye. Whatever you do, don t make any sudden or drastic changes to your present set-up, rather, evolve your position gradually, changing each parameter (such as saddle height) one at a time, by no more than 3 mm every two weeks or so. More dramatic alterations may be made in the off-season. The baseline: your present bicycle Begin by carefully measuring, in millimeters, the following frame dimensions. Make sure the top tube is level, or, for frames with sloping top tubes, that the bicycle is on a level surface and the tires are of identical make, width, pressure, and condition: t t h s s s d s t s d h

2 1. t s seat tube length (or frame size center-to-center ). From the radial center of the bottom bracket to the junction of the centers of the seat and top tubes, in a line parallel to the seat tube. 2. t t top tube length. The distance between the center of its junctions with seat and head tubes. 3. t sθ seat tube angle. As specified by the manufacturer, or drop a plumbline from the top tube at the point exactly over the center of the bottom bracket. Measure the distance from this point to the junction of the centers of the seat and top tubes, then divide this by t s, take the inverse sine, and subtract from e stem extension. From the center of the steering tube to the center of the handlebar clamp, in a line parallel to the ground. 5. c crankarm length. As specified by the manufacturer. 6. h s saddle height. Same starting point as #1, but continued up to the well of the saddle. 7. s s saddle set-back. The perpendicular distance from a plumbline hung over the nose of the saddle to the center of the bottom bracket. 8. d saddle-handlebar difference. Measure perpendicularly from the ground to the well of the saddle (d s ) and from the ground to the top edge of the handlebars (d h ), then subtract the two values. Measuring the body The following dimensions should be taken at the same time of day, such as just after rising, since the pull of gravity will compress the spine and reduce torso length as the day wears on. In socks and cycling shorts, stand on a hard, even surface, feet about 6-8 inches apart from instep-to-instep (or so that legs are perpendicular to the ground), knees completely extended, in front of a smooth wall. Tape a sheet of blank paper to the wall at the point opposite your crotch. Have a partner (the measurer, and someone you trust!) sit on floor to either side of you and push a 2-foot long 2 4 up between your legs, with the 2 top edge facing up and kept level, and the front edge butted against the paper on the wall (attach a torpedo level to the top edge and be sure to monitor the levelness of the board, giving feedback to the measurer). When the board is level and the measurer is exerting enough pressure, mark the position of the end of the top surface of the board on the paper. The distance from the mark to the floor is inseam length i. What is sufficient pressure? Enough to compress the chamois liner of the shorts, but not so much that you are lifted off the floor. Take 3-4 measurements, always being careful to keep the board level, and average the closest 3 values. Usually, the first one is a bit short and should be discarded. Next, measure torso length, standing in front of the wall in the same position. Tape a sheet of blank paper to wall across from your sternal notch (the depression at the top of the sternum, just below the Adam s Apple). Gently insert a straight ¾ dowel (about 12 long) in this depression and move forward until the face of the dowel is flush against the wall. Once again, you need to strap a small level to the dowel, but this time, the measurer checks it. When it s level, mark the lowest point at which the dowel contacts the wall, and label this measurement n, for strernal notch height. Repeat several times, and average the 3 closest measurements. Subtract inseam length i from n to obtain torso length t. Now, take a seat, and with the lower leg exactly vertical and the upper leg horizontal, obtain lower leg length by measuring from the floor to the knee joint separation, which is located just above the proximal end of the fibula. Subtract this from inseam length to obtain upper leg length l u. One last anthropometric data point... arm length a. With elbow joint fully extended and arm raised to 45 below horizontal, measure from the acromial (lateral) end of the clavicle (bump on top of shoulder) to the distal end of the ulna (bone directly below knuckle of pinky finger). Finally, measure lower arm length a l by having the person being measured sit at a table as though they were about to arm-wrestle you. With the arm perpendicular to the table (i.e., vertical), measure from the table surface to the distal end of the ulna. 2

3 a n i Anthropometric information for male competitive road cyclists. RIDER DATA (mm) RATIOS i n t a r1 r MEANS ±SD 853 ± ± ± ± ± ±0.016 i = inseam; n = height of sternal notch; t = torso (n - i); a = arm; r1 = t/n; r2 = a/n 3

4 Calculating frame dimensions Record all these values, and keep a careful record of each change in bicycle set-up (date, parameter, amount of change), then, calculate bike dimensions in mm as follows: 1. seat tube length = i 0.65 or top tube length = (t + a) or seat tube angle = 1.135{90 - [sin -1 (l u /i)]} 4. stem extension = (t + a) or crankarm length = i 0.203; the conventional wisdom used to be to add 2.5 mm for time trials, 5.0 mm for pure hillclimbs, but from recent research, there appears to be no advantage to this, and longer cranks may actually decrease comfort in the aero position 6. saddle height = i , taking foot length, pedal/cleat stack height, shorts, and saddle firmness into account; generally, the saddle is moved up and forward for events of shorter duration requiring higher power outputs, down and back for road races and hilly terrain 7. saddle set-back = l u 0.190; this is, admittedly, the most questionable formula, since saddle length and shape can significantly affect the fore-aft position. Better, perhaps, is the KOPS (Knee Over Pedal Spindle) referencing guideline, where the position of the tibial tuberosity (bump just below the kneecap) is measured in relation to the pedal spindle, with the bike on a level surface. As a variant of this, some recommend aligning the plumb line with the front edge of the knee cap and the end of the crank arm. Dr. Andrew Pruitt recommends that with the pedal at bottom dead center (6 o clock), the tibia should be vertical, and a line drawn from the femoral head in the hip to the center of the knee joint, when extended, should form a angle with the tibia (to obtain this measurement, you need a goniometer, such as is available from He observes that for the vast number of elite cyclists he has measured, the mode range for this measurement is 30 with a very small standard deviation saddle-handlebar difference = a Remaining specifications, such as wheelbase, chainstay length, head tube angle/fork rake, and bottom bracket height should be determined by desired handling characteristics and intended use of the bicycle. For instance, a touring bicycle will have a relatively longer wheelbase and chainstays, with a shallower head tube angle and/or less fork rake, all of which make for more stable but slower handling, whereas a racing bike will be just the opposite, with a shorter wheelbase and steeper head tube angle and/or more fork rake, for more responsiveness. How does it all look and feel? Once again it must be emphasized that these formulae should not be taken hard and fast, or substituted for a visual inspection and perceptual feedback: What is the overall impression of the how the bike fits? Is the saddle too high? Is your knee joint too extended at the bottom of the pedal stroke? Do your hips rock noticeably? Is the saddle too low? Is your knee joint angle markedly acute? Do you appear to be bunched up? Is your torso angle markedly upright, even when you are on the drops? Do you have trouble sustaining your position on the handlebar drops? How near to horizontal is your back when you are on the drops? If a plumb line were dropped from your nose, does it fall between the rear edge and the centerline of the handlebars? 4

5 Are you too extended, or stretched out? Do you strain at all to reach the brake lever hoods or handlebar drops, such that you seldom use these positions, and are most always on the tops of the handlebars? Are your arms locked out when you are riding in the drops? Do you find yourself frequently riding up on the nose of the saddle? Is there any pain or discomfort? Anterior knee pain may indicate a saddle that is too low or too forward, while discomfort posterior to the knee (e.g., the distal end of the hamstrings) is often caused by a saddle that is too high or too far back. Forefoot cant affects knee alignment, and therefore knee comfort. Most people tend to ride knocked-kneed, and require some amount of forefoot varus (canting of the forefoot upward on the inside), while others will require forefoot valgus (downward canting of the forefoot on inside). Specially-made shims called The Wedge ( can correct for either condition, while the Specialized BG line of shoes has a very minor amount of forefoot varus, equivalent to one Wedge. Some individuals will need more correction than this, or different degrees of correction for each foot, and these shoes may be inappropriate in such cases, as well as those with a neutral forefoot or who are in need of valgus correction. Lower back pain/discomfort may be caused by too much extension (a position that is too stretched out ), while too little extension can result in neck pain. Pain in between the shoulder blades may indicate handlebars that are too wide. 5

6 On-line resources (time trial-specific) References Burke, E.R. Proper fit of the bicycle. Clinical Sports Medicine 13(1):1-14, January Coyle, E.F., L.S. Sidossis, J.F. Horowitz, and J.D. Beltz. Cycling efficiency is related to percentage of Type I muscle fibers. Medicine and Science in Sports and Exercise 24(7):782-88, July Horowitz, J.F., L.S. Sidossis, and E.F. Coyle. High efficiency of type I muscle fibers improves performance. International Journal of Sports Medicine 15:152-57, April Martin, J.C., and W.W. Spirduso. Determinants of maximal cycling power: crank length, pedaling rate and pedal speed. European Journal of Applied Physiology 84(5):413-8, May McDaniel, J., J.L. Durstine, G.A. Hand, and J.C. Martin. Determinants of metabolic cost during submaximal cycling. Journal of Applied Physiology 93(3):823-8, September Peveler, W.W. Effects of saddle height on economy in cycling. Journal of Strength and Conditioning Research 22(4):1355-9, July2008. Fit session checklist with torpedo level and rubber bands ¾ (20 mm) diameter dowel with level attached 3. spool, line, and lead sinker or plumb bob 4. metric tape measure 5. masking tape 6. Sharpie marking pen 7. 2 sheets blank paper, pencil, and cellophane tape 8. fitting sheet and fit article 9. The cyclist should be in riding shorts, socks, and tank-style top. 10. For the visual assessment, the bicycle should be mounted in a stationary trainer on a level surface. 6