opensus
Getting started: your first suspension in 5 minutes
The fastest way in is to open the Formula SAE example, move one hardpoint, and watch the curves change. This page walks through that, then through starting your own design.
1. Open the tool
Go to opensus.app/app. It runs in the browser with nothing to install. Your design saves itself in the browser as you work, so a reload never loses anything.
The screen has four parts:
| Area | What it holds |
|---|---|
| Left panel | Inputs, split into Car, Front and Rear |
| 3D view | The suspension. Click a point to edit it, drag it, or hover to see its name |
| Right readout | Camber, toe, caster, kingpin inclination, scrub radius, trail, roll center, anti geometry and ride numbers at the current position |
| Bottom | Analysis tabs: Kinematics, Cornering and braking, Bumps and transients, Compliance, Loads |
Drag the edges between the panels to resize them, or press Expand to make the 3D view fill the window.
2. Load an example
Open Project → Examples → Formula SAE car. It is a pushrod double wishbone car on 10 inch wheels, about 300 kg with a driver. Its full hardpoint list is on the Formula SAE example page.
3. Change a hardpoint
In the left panel, choose Front. Under Points, click the Lower arm, front inner Z value and type a new height, or click the point in the 3D view and drag its handle. The charts in the Kinematics tab (Heave) redraw as you change it:
- Camber and Camber gain: how the wheel leans as it moves up and down. See camber gain.
- Toe (bump steer): how much the wheel steers itself over a bump. See bump steer.
- Roll centre height: where the body rolls about, and how far it moves. See roll center.
On the docs example geometry, raising the lower arm's inner pivots by 10 mm raises the roll center by 25 mm and increases camber gain by about a fifth. The roll center guide gives exact numbers.
4. Start your own design
Choose Project → New, then for each axle pick a Type under Suspension: Double A-arm (pushrod and rocker), MacPherson, 5-link, semi-trailing arm, or blank to build any linkage from points, links and joints.
- On the Car panel, enter mass, wheelbase, weight distribution and CG height.
- On Front and Rear, type your hardpoints into the Points table. Coordinates are in mm from the axle line, the centreline and the ground; see coordinates.
- Enter static camber and toe: where the wheel should sit with the car loaded. opensus then solves the spring perch that holds the car there.
- Check the status line under the type. Valid linkage with 1 free motion means the corner moves the way a real suspension does. Anything else comes with a plain-language message saying what is missing.
5. Go further
- Cornering and braking solves the whole car at a steady acceleration: roll, pitch, tire loads and understeer.
- Bumps and transients simulates kerb strikes, bumps, step steer and braking through time, with springs, dampers and sway bars.
- Compliance shows how much the geometry lets the wheel steer and camber under load.
- Loads runs design load cases and gives the worst force in every link and joint.
To share a design, or to open one from a link, see the import format.