Enter your measurements and your bike's geometry, then move the saddle, stem and spacers and watch your position change. Knee and torso are judged against the calculator's targets for your discipline and riding level.
A geometric model with average body proportions, not a measurement of you. Use it to compare setups and to see which way a change moves you, then check on the bike.
Showing an example rider (1780 mm tall, 820 mm inseam). Enter your own measurements. Crank length 170 mm is the example's: enter yours under Saddle and cranks.
You
How the fit constructor works
Enter your height, inseam and discipline, or carry them over from the bike fit calculator. Then enter your bike’s stack and reach and its head tube and seat tube angles from the geometry chart, plus your stem and spacers. Until you do, the constructor shows an example bike and says so.
Move the saddle, stem, spacers and elbow bend, and the side view of the rider follows. The constructor shows:
- the knee angle at the bottom of the pedal stroke, against 145–155°, the same range the position check uses;
- the torso angle, against the calculator’s target for your discipline and riding level;
- shoulder and elbow angles on aero bars;
- knee and hip angles at the top of the stroke, as numbers only, to compare crank lengths.
One button sets spacers (0–40 mm) and stem angle to bring your torso as close to its target as your stem allows. You can save the setup, angles and advice as a PDF report.
It is a geometric model, not a measurement of you. Body segments are average fractions of height, and the leg is calibrated so that the calculator’s saddle height puts your knee in the middle of the range. Use it to compare setups and see which way a change moves you, then check the result on the bike with the position check.
Related guides: Torso angle in bike fitting · Knee angle in bike fitting · Shoulder and elbow angles · Crank length and saddle height
Frequently asked questions
Where do I find stack and reach for my bike?
In the geometry chart for your frame size, usually on the manufacturer’s website. Stack is the vertical and reach the horizontal distance from the center of the bottom bracket to the top of the head tube. The head tube and seat tube angles are in the same chart. Stem length, stem angle and spacers you can read or measure on your bike.
How accurate are the angles?
They are estimates, which is why they are marked with ≈. The model uses average body proportions, which can be off by a couple of centimeters per segment for any one person, and a side view cannot show elbows pointing outward. Use the angles to compare two setups, not as a measurement. For your real angles, take a side-on photo or video in the position check.
Why are shoulder and elbow angles shown only on aero bars?
On drop and flat bars this model reads the shoulder about 10° below the usual range, even in the calculator’s own road position. A likely cause is that a side view cannot show elbows pointing outward. Until that is solved, the constructor does not show these two angles on drop and flat bars.
Can it tell me which crank length to choose?
Not directly. It shows knee and hip angles at the top of the stroke for the crank length you enter, without a target range, because we found no source for one. Studies found that cranks 5–10 mm shorter reduced hip and knee flexion in parts of the stroke without changing mean power.
Does it work for kids’ bikes?
Yes, with more caveats. The example bike takes its wheel size from the kids’ size chart, and its crank length and frame angles from real kids’ bikes. We found no published stack and reach for kids’ frames, so the frame is estimated, and average body proportions fit children less well than adults. The knee angle is shown without a verdict, because the kids’ saddle height is set lower on purpose so the child can reach the ground.
Sources
- Drillis R, Contini RJ. Body segment parameters. Report 1163-03. New York University, School of Engineering and Science; 1966. Segment-to-height fractions as reproduced in Winter DA. Biomechanics and Motor Control of Human Movement. Wiley.
- Upper body segment lengths as a proportion of height in children. ISBS Conference Proceedings Archive. Link
- LeMond G, Gordis K. Greg LeMond’s Complete Book of Bicycling. New York: Putnam; 1987.
- Holmes JC, Pruitt AL, Whalen NJ. Lower extremity overuse in bicycling. Clin Sports Med. 1994;13(1):187–205. (Knee range as cited in later literature.)
- Ferrer-Roca V, Roig A, Galilea P, García-López J. Influence of saddle height on lower limb kinematics in well-trained cyclists: static vs. dynamic evaluation in bike fitting. J Strength Cond Res. 2012;26(11):3025–3029. Link
- Empfield D. Coordinate Predictors Versus Body Angles in Road Bike Fit. Slowtwitch; 2012.
- Empfield D. Devising a static tri-fit system. Slowtwitch; 2009-06-29.
- Reynolds S, Chidley J, Briley S, Outram T. The impact of minor crank length adjustments on lower body cycling kinematics. Sports Biomechanics. 2025. doi:10.1080/14763141.2025.2511755 Link
- Li J, Wang Q, Zhang Y, et al. Effects of crank length on cycling efficiency, sprint performance, and perceived fatigue in high-level amateur road cyclists. Journal of Exercise Science & Fitness. 2025. doi:10.1016/j.jesf.2025.100384 Link
- Example bike geometry: SCOTT Scale RC (2025) and woom kids’ bikes, as listed on bikeinsights.com (read 2026-10-30). Link