Rider Triangle: motorcycle ergonomics calculator & simulator

Enter rider and bike measurements. Pin a setup, change a control position, then compare modeled knee and elbow angles. Geometry only, not a comfort or safety score.

Pick a bike style

Examples, not manufacturer specs.

Example sizes. Replace with yours.

Knee 69.4° · Elbow 138.7° ReachableResults Compare Save

Measure. Adjust.

Where do I measure?

Units

02Your body

Estimate from height

Height mm

Hip-to-shoulder length mm

Upper arm length mm Shoulder to elbow.

Forearm + hand reach mm Elbow to grip center.

Hip-to-knee length mm

Knee-to-foot length mm Knee to footpeg.

Rider inseam mm Crotch to floor. Seat comparison only.

03Your motorcycleSet by the bike style

Bar reach from hip mm Forward is positive.

Bar height above hip mm Below is negative.

Footpeg forward of hip mm Behind is negative.

Footpeg below hip mm Enter as positive.

Seat height mm Ground to seat.

Torso forward lean ° From vertical. Your assumption.

Torso lean 15° For an exact angle, use the field above.

All fields required.

THE RIDER TRIANGLE

Your position

Computed locally

SIDE VIEWFROM YOUR HIP

NowBike faces right

Knee angle 69.4°Straight = 180°

Elbow angle 138.7°Straight = 180°

Forward lean 15°Your assumption

Inseam − seat +22 mmFeet flat not guaranteed

Hip angle 83.7°Torso to thigh

Hands and feet both reach.

Reachable is not comfortable or safe. Check the real motorcycle.

BEFORE / AFTER

Compare two setups.

Pin this setup, then change a size.

Lasts this session.

How far each hand and foot must reach

Needed distance against the shortest and longest reach of each limb
Contact	Distance	Possible range	Result
Handlebar reach	589.9 mm	60 mm to 630 mm	Within range
Footpeg reach	531.4 mm	70 mm to 928 mm	Within range

Angle = arccos((A² + B² − D²) ÷ (2AB)). A, B: the two bone lengths. D: hip to footpeg, or shoulder to grip.

Too far or too near for the limb? The page says unreachable. It never bends the limb to fit.

Seat width, sag, boots and stance are not modeled.

Inputs used Stored in mm

Hip-to-shoulder length: 504 mm
Upper arm length: 285 mm
Forearm + hand reach: 345 mm
Hip-to-knee length: 429 mm
Knee-to-foot length: 499 mm
Torso forward lean: 15°
Bar reach from hip: 690 mm
Bar height above hip: 300 mm
Footpeg forward of hip: 180 mm
Footpeg below hip: 500 mm
Seat height: 820 mm
Rider inseam: 842 mm

A model, not a verdict.

Rider Triangle · Method 1.1.0 · Includes example inputs · Millimeters / degrees · ridertriangle.com

KEEP IT

Save your setup

Setup name

Plans stay in this browser. The plan file includes the baseline.

Try a change

Nothing changes until you apply. Guides: bars, pegs, seat.

Change Amount 20 mm

Elbow angle: 138.7° → 135.7°

Unchanged: Knee angle, Forward lean, Inseam − seat, Hip angle.

Passenger reach

Passenger knee reach. Not drawn.

Seat forward of hip mmBehind is negative.

Seat above hip mm

Thigh length mm

Shin length mm

Peg reach mm

Peg drop mm

Knee angle: 68.2°
Hip to footpeg: 504.9 mm
Reachable range: 0 mm to 900 mm
Result: Within reach

Geometry only. No comfort, foot support or grab-rail check.

How the calculation works

Body and bike sizes go in, and knee and elbow angles come out.

Worked example

Default measurements. Hip-to-shoulder 504 mm, upper arm 285, forearm 345, thigh 429, shin 499, torso lean 15°, bar 690 forward and 300 up, peg 180 forward and 500 down.

Shoulder: x = 504×sin(15°) ≈ 130.4 mm, y = 504×cos(15°) ≈ 486.8 mm.
Shoulder to bar: 589.9 mm. With a 285 mm upper arm and a 345 mm forearm, the elbow is about 138.7°.
Hip to peg: 531.4 mm. With a 429 mm thigh and a 499 mm shin, the knee is about 69.4°.

Elbow angle ≈ 138.7°, knee angle ≈ 69.4°. A straight limb is 180°.

Assumptions

Flat side view. Width, seat shape, boots and sag are ignored.
Bars and footpegs are measured from your hip. Your torso lean sets the shoulder.
Lean is your choice, not a measured posture.

When to use this

Compare seat, bar or peg changes.

Common mistakes

Measuring from different hip points or bikes.
Reading unreachable as a small measuring error.

Rider triangle basics

What is a rider triangle?

The rider triangle is the shape between your seat, handlebars and footpegs. It sets how far arms and legs reach.

References

ReferencesMotorcycle Safety Foundation Cycle World fit tips Harley-Davidson ergonomics

Not a fit score.
Geometry only.

Read the method

Measure your body and bike

How to measure your motorcycle rider triangle

How knee and elbow angles are calculated

Verification checklist

Seat height and riding position guides

See the 6 data guides

Motorcycle riding positions by style

Five bike styles.

Browse 02

Motorcycle seat height vs inseam chart

26 to 38 in inseams, 680 to 920 mm seats.

Open 03

Handlebar risers: elbow angle and reach

Bars 10 to 50 mm higher or further back.

Footpeg position and knee angle

Pegs 10 to 50 mm lower or further back.

Seat height change and knee angle

10 to 50 mm of seat change.

Motorcycle ergonomics glossary

Plain definitions of 21 terms.

Read

All guides

Before you ride.

Does this tell me which motorcycle fits?

No, it does not rate comfort or fit. Check reach, clearance and control on the real motorcycle.

Can I enter measurements in inches?

Yes, switch units beside the measurements. Calculations, share links and saved plans all use millimeters.

What does an unreachable result mean?

Your limbs cannot span that distance, so no angle is shown. Recheck your measurements, or try the bar or peg closer or with more lean.

Where does my data go?

Calculations run on your device, and saving is optional. A share link holds your measurements, and anyone with the link can read them.

How does seat height compare with inseam?

Gap = inseam (floor to crotch) minus seat height (floor to seat). A positive number does not mean both feet reach the ground flat: seat width, sag, boots and road slope also count.

What does the knee angle show?

It is the bend between thigh and shin, and 180° is a straight leg.