Methodology & limitations
Understand what is calculated, what is entered, and what remains unknown.
Calculation rules
Measure your limb lengths on the exact motorcycle and setup, and the handlebar and footpeg positions from your hip.
Pick a torso lean. The tool finds each angle of the arm and leg triangles from their side lengths (the law of cosines). A joint that cannot reach is marked unreachable.
Use the drawing to compare setups, not to judge comfort, footing or safe control.
Limits that matter
A 2D diagram cannot guarantee comfort, footing, control reach, clearance, or safe operation. Always check on the real motorcycle.
Examples and plan files
Styles and their tables are examples, not manufacturer specifications or a motorcycle database. A plan file is fully checked on your device before it opens. Missing measurements stay unknown unless you use Estimate from height.
Estimating body lengths from height
Estimate from height fills the six body fields with shares of your height (inseam grows a little faster), rounded to the millimeter. These are averages; people differ by several centimeters, so measuring is better.
| Part | Share of height | Source |
|---|---|---|
| Torso | 0.288 | Winter: shoulder minus hip (0.818 - 0.530) |
| Upper arm | 0.163 | ANSUR II less de Leva joint offsets |
| Forearm | 0.197 | ANSUR II: mean of men and women |
| Thigh | 0.245 | Winter: hip minus knee (0.530 - 0.285) |
| Shin | 0.285 | Winter: knee height (knee to sole) |
| Inseam | 0.481 | ANSUR II: mean of men and women, at 1750 mm |
How we got these shares
Three shares come from Winter, Biomechanics and Motor Control of Human Movement, Figure 4.1 (after Drillis and Contini, 1966). They are shoulder height 0.818, hip 0.530 and knee 0.285.
Two more come from ANSUR II (2012 U.S. Army survey, Natick TR-15/007; 4,082 men, 1,986 women). Mean crotch height is 0.482 of mean height for men and 0.480 for women, and forearm to grip center is 0.199 and 0.195. The studio uses the means, 0.481 and 0.197. Crotch height rises 0.546 mm per mm of height, so the studio uses that rate, with 842 mm at 1750 mm.
Upper arm is the ANSUR II shoulder-tip to elbow length, 0.191 of height, less the joint-center offsets in de Leva, 1996. That gives 0.163 for men and 0.162 for women; the studio uses 0.163. Forearm is measured from the back of the elbow, so it may run 1 to 2 cm long.
ANSUR II measured U.S. Army soldiers. The inseam share is barefoot, so boots add sole height that the estimate leaves out. The shin also ends at the sole, so boots and a ball-of-foot stance bend the knee more. Seat sag is left out.
How this model was checked
A test recomputes every elbow and knee angle from the drawn joint positions and compares it with the reported angle.
Short version: at 1750 mm the examples bend the elbow to about 135 to 139°. That is inside the 131 to 163° the studies below measured on real riders.
How we compared with studies
Measured: twenty men of 171.5 to 178.6 cm sat with average elbow angles from 131 degrees (scooter) to 160 degrees (touring motorcycle).
Source: Lundin and others, 2024, Traffic Injury Prevention 25(7), 956-967.
Ten women of 157.6 to 168.5 cm on a touring motorcycle averaged about 163 degrees. Source: Lundin, Oikonomou, Svensson and Iraeus, 2025, Chalmers University of Technology report 2025:01.
These are 3D angles on specific motorcycles and small groups.
At the same lean, a rider needs about 1640 mm of height to reach every example's bar. At 1550 mm the bars must come 16 to 33 mm closer.
The model holds hip and shoulder still, but a real rider can shift forward or lean more. In a lab study of seated pointing, the shoulder girdle added about 4 cm of reach (Roby-Brami and others, 2016, Motor Control). So a rider may reach a bar the drawing shows out of reach. Grips sit wider than the shoulders, so a 3D measurement of the same pose reads straighter than this side view.
Knee, inside angle: 74 ± 8° for 120 Indian men (mean 168 cm) who set a test rig to their own chosen position. Source: Arunachalam, 2021, PhD thesis, IIT Guwahati, Table 4.3. Across the bike types tested, 20 men averaged 54 to 74° (Lundin 2024). Examples at 1680 mm: standard 73°, touring 77°, adventure 77°, sport 64°, cruiser 102°. We found no measured sport or cruiser knee.
Lean: the sport example leans 25 degrees from vertical and the cruiser 8. A study of photographs of 12 motorcycles reports about 65 (sport) and 85 (cruiser) degrees from horizontal, or 25 and 5 from vertical. Source: Hale, Pelowski and Bhise, 2007, SAE 2007-01-0438, abstract.
ANSUR II measured on the skin. Hip point to shoulder tip is 0.307 of height for men and 0.301 for women, against the 0.288 used here. Hip point to knee is 0.233, against 0.245. At 1750 mm that is about 3 cm and 2 cm. Hip points differ by method, so measure yourself.
The example bars were corrected on 2026-10-13. Before that they sat too close.
On 2026-10-15 the estimated upper arm changed from 0.186 of height (skin length) to 0.163 (joint centers). Estimated elbows read straighter. Saved plans keep their numbers.
Limits of this check:
- Lean and hip stay fixed as rider size changes, so taller riders come out more bent and shorter riders straighter. If a short rider is out of reach, reduce Bar reach from hip or raise Torso forward lean.
- The torso is one straight line; a real spine curves.
- Grip and peg width are ignored.
Saved files
Plan files keep your inputs and the method version. Table files and the printed report list every result row. A saved plan stays in this browser until you delete it or clear site data. Saved plans and plan files include the pinned baseline; share links do not.
Corrections and independence
Report calculation problems from the Contact page. Send an example that others can repeat, with no private details. Advertising does not change the calculations or examples.