Suspension Geometry Calculator

Input Geometry Data

Track Width (mm)

Tire Width (mm)

Wheel Offset (mm)

Kingpin Offset (mm)

Loaded Wheel Radius (mm)

CG Height (mm)

Ride Height Change (mm)

Lower Arm Length (mm)

Upper Arm Length (mm)

Lower Arm Angle (deg)

Upper Arm Angle (deg)

Spring Pickup Distance (mm)

Damper Pickup Distance (mm)

Ball Joint Spacing (mm)

Caster Angle (deg)

Steering Arm Length (mm)

Tie Rod Angle Change (deg)

Use measured values from one axle corner for better consistency. This tool gives engineering estimates, not a substitute for full kinematic simulation.

Example Data Table

Parameter	Example Value	Unit	Why It Matters
Track Width	1600	mm	Influences roll leverage and weight transfer.
Lower Arm Length	380	mm	Shapes instant center location and camber behavior.
Upper Arm Angle	-6.0	deg	Controls camber gain during wheel travel.
Caster Angle	6.5	deg	Builds steering trail and straight-line stability.
Spring Pickup Distance	145	mm	Sets motion ratio and wheel rate relationship.
Ride Height Change	20	mm	Shows how setup changes affect geometry.

Formula Used

Camber gain is estimated from the angular difference between upper and lower control arms, normalized by their lengths and wheel travel.

Camber Gain ≈ [tan(upper arm angle) / upper arm length − tan(lower arm angle) / lower arm length] × 57.2958 × 10

Camber Change ≈ Camber Gain × ride height change ÷ 10

Roll Center Height ≈ (track width ÷ 2) × (upper arm angle − lower arm angle) ÷ 57.2958

Mechanical Trail ≈ tan(caster angle) × (loaded wheel radius × 0.55)

Motion Ratio ≈ spring pickup distance ÷ lower arm length

Wheel Rate Factor ≈ motion ratio²

Bump Steer Change ≈ tie rod angle change × ride travel ÷ steering arm length

These equations provide practical estimates for layout studies, garage tuning, and comparative design work. Exact race-car development still needs full 3D suspension kinematics and compliance analysis.

How to Use This Calculator

Measure the suspension from a fixed ride-height reference.
Enter arm lengths, arm angles, caster, and wheel data.
Add the expected ride-height change for bump or setup adjustment.
Click Calculate Geometry to place results above the form.
Review camber gain, roll center, scrub radius, and trail together.
Export the output as CSV for records or PDF for setup sheets.

Frequently Asked Questions

1. What does this calculator estimate?

It estimates camber gain, roll center height, motion ratio, scrub radius, trail, bump steer tendency, and related setup indexes from measured suspension dimensions.

2. Is this suitable for race cars?

Yes, for early setup comparisons and workshop checks. Final race development should still use precise kinematic software, alignment rigs, and track validation.

3. Why is ride height change important?

Ride height change alters arm angles and wheel travel. That shifts camber, roll center, steering response, and tire loading during braking, cornering, or spring changes.

4. What does motion ratio tell me?

Motion ratio links wheel movement to spring movement. A lower ratio reduces effective wheel rate, while a higher ratio increases spring influence at the tire.

5. Can I use inches instead of millimeters?

Use one unit system consistently. This file is labeled in millimeters, so convert all measurements first to keep results internally consistent.

6. What causes large scrub radius values?

Wheel offset, tire width, and kingpin offset drive scrub radius. Large values can increase steering kickback, braking sensitivity, and uneven surface reactions.

7. Does this replace a full suspension model?

No. It is a practical engineering estimator for rapid decisions. Full vehicle models also include chassis compliance, dynamic loads, tire behavior, and steering geometry details.