opensus docs

opensus is a free, browser-based 3D suspension kinematics design tool for race cars. You enter the hardpoints of a double wishbone, MacPherson strut, multilink or semi-trailing arm suspension, and camber gain, bump steer, roll center migration, motion ratio, anti-dive and anti-squat update as you move them. It also estimates compliance steer and the load in every link, and simulates the whole car through corners, braking and bumps. Nothing to install: it runs at opensus.app/app.

These docs teach the engineering as well as the buttons. Every worked example uses numbers you can check by hand and reproduce in the tool with one click.

Start here

  • Getting started: Load an example or start a new design in opensus, enter hardpoints, set static camber and toe, and read camber gain, bump steer and roll center from the live charts.
  • Coordinates, units and axes: The opensus coordinate system for suspension hardpoints: ISO 8855 axes (X forward, Y left, Z up), the origin at the axle line, centreline and ground, millimetres, and how to switch to SAE J670 or CAD axes.
  • Import format: Open a suspension design in opensus from a URL. The ?example= and ?design= parameters, the JSON schema for hardpoints, camber and toe, every point name for each suspension type, and project files.

Suspension types

  • Double wishbone suspension: How a double wishbone (SLA, double A-arm) suspension works, which hardpoints set camber gain, roll center and bump steer, and a worked example geometry you can open in opensus.
  • MacPherson strut suspension: How a MacPherson strut suspension works, its hardpoints, why its camber gain is low and its roll center moves fast, and how opensus models the strut, with results for the default strut.
  • Multilink suspension: How a five-link (multilink) suspension locates a wheel with five rigid links, how opensus finds its virtual steering axis and instant centers, and results for the default five-link rear.

Metrics

  • Roll center: How to find the roll center of a double wishbone suspension from the front-view instant center, the formula for roll center height, a worked example (89.9 mm), and why roll center migration matters.
  • Camber gain: Camber gain is the change in camber per unit of wheel travel, set by the front-view swing arm length. Formula, a worked example (-0.317 degrees per 10 mm), and how body roll and camber gain combine.
  • Bump steer: Bump steer is toe change with wheel travel. What causes it on a double wishbone, how tie rod height and length set it, a measured example (0.107 degrees per 10 mm from a 5 mm tie rod error), and how to read it in opensus.
  • Scrub radius, kingpin inclination, caster and trail: How the steering axis sets scrub radius, kingpin inclination (KPI), caster and mechanical trail, with formulas and a worked example: 5.19 degree KPI and caster, 39.1 mm scrub radius, 15.9 mm trail.
  • Motion ratio, wheel rate and ride frequency: Motion ratio is spring travel per unit of wheel travel. How it sets wheel rate (spring rate times motion ratio squared), ride rate with the tire, and ride frequency, worked through for the opensus Formula SAE example.
  • Anti-dive, anti-squat and anti-lift: How side-view suspension geometry resists pitch under braking and acceleration. The anti-dive formula from the side-view instant center, inboard versus outboard brakes, and a worked example (12.6 percent anti-dive) on the opensus Formula SAE example.

How-to guides

  • How to reduce bump steer on a double wishbone: A step-by-step method to find and remove bump steer in opensus: read the toe curve, move the tie rod inner pivot height to fix the slope and its length to fix the curvature, then check roll steer.
  • How to set roll center height on a double wishbone: Which double wishbone pivots move the roll center and by how much, with measured effects in opensus (raising the lower inner pivots 10 mm raises it 25 mm), and the camber gain trade-off that comes with it.

Analysis

  • Compliance steer and camber from suspension geometry: How opensus estimates compliance steer and compliance camber from geometry alone, with every joint at one reference stiffness. The load cases, the understeer summary in degrees per g, and what drives the numbers.
  • Suspension load cases and link loads: How opensus runs design load cases (combined cornering and braking, bumps, acceleration, kerb strikes) and reports the worst tension, compression and joint force in every suspension link, pushrod, spring and pivot.

Examples

  • Formula SAE car: Complete suspension hardpoints and kinematic results for the formula sae car example in opensus: camber, caster, roll center, anti-dive, motion ratio and ride frequency.
  • E30-style sedan: Complete suspension hardpoints and kinematic results for the e30-style sedan example in opensus: camber, caster, roll center, anti-dive, motion ratio and ride frequency.

Reference

  • Methodology: How opensus solves suspension kinematics with a general rigid-body constraint solver, finds instant centers from real motion, models the whole car by virtual work, simulates transients, and the assumptions and limits that apply.
  • Validation: Measured accuracy of the opensus suspension solver against an independent closed-form double wishbone solution and hand calculations: wheel position within 0.000001 mm, angles within 0.000003 degrees, roll center and steering geometry exact.
  • opensus compared with other suspension design software: An honest comparison of opensus with established suspension kinematics tools such as OptimumK, SusProg3D and Lotus suspension analysis software, and with CAD sketches: what each is good at and when to use which.

Last updated 2026-11-07 · View as Markdown