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Measurement Guide

Simulation accuracy is bounded by input accuracy. This page covers the parameters that are easiest to get wrong or skip, why each one matters to the model, and how to measure it — with a pointer to where it's entered in ARD.

Center of Gravity (COG) Height

COG height directly sets weight transfer during acceleration, braking, and cornering. Getting it wrong distorts tyre load predictions and skews lap time and handling results — including how sensitive the model looks to other setup changes, like suspension tuning.

How to measure:

  • Calculate it from geometric relationships and corner weight distribution
  • Or measure directly with corner weight scales and a tilt test (lift one axle, measure the weight shift at the other end)

Entered in Chassis.

Anti-Roll Bar Stiffness

Anti-roll bars set the front/rear roll stiffness split, which is one of the main levers on understeer/oversteer balance. A wrong stiffness value misrepresents that balance in Handling Analysis and leads the model toward the wrong setup recommendations.

How to measure:

  • Calculate torsional stiffness from bar diameter, length, and material properties, combined with the mounting/lever geometry
  • Validate with a deflection test under a known load

Entered in Anti-Roll Bars.

Torque Curves, Gear Ratios, and Aerodynamic Coefficients

Torque curves drive acceleration and lap time modeling — get the shape across the RPM range right, not just peak power. Gear ratios set wheel torque, top speed, and shift points. Aerodynamic drag (Cd) affects top speed, acceleration, and energy use.

How to measure:

  • Torque curves and gear ratios: manufacturer specs or dyno data are more reliable than published references, which often round or approximate
  • Aerodynamic coefficients: wind tunnel or CFD data if you have it; otherwise a comparable published vehicle as a starting estimate

Entered in Engine, Gears, and Aerodynamics.

Motion Ratios

Motion ratio is the relationship between wheel travel and spring/damper travel — it determines the effective wheel rate for a given spring, so an error here changes your suspension tuning without you touching a spring.

How to measure:

  • Compare wheel displacement against spring/damper displacement directly, or derive it from suspension geometry

If you have pickup-point geometry instead of a measured curve, ARD calculates motion ratio for you — see Kinematics.

Camber & Toe

Camber (tyre tilt) affects cornering grip, tyre wear, and handling balance. Toe (wheel angle relative to the chassis) affects straight-line stability, turn-in response, and tyre wear.

How to measure: laser alignment systems, string methods, or digital toe/camber gauges all work — consistency between corners matters more than which tool you use.

Entered as static values in Initialization, or as curves vs. wheel travel in Kinematics.

Suspension Kinematics

Kinematics governs how the wheel moves relative to the chassis through its travel — camber gain, toe change (bump steer), roll centre migration, and anti-dive/anti-squat all come from this geometry. Get the pickup points wrong and every downstream handling and load-transfer prediction inherits the error.

Key concepts:

  • Roll centre — where lateral force transfers to the chassis without engaging the springs/dampers. Its height and location set how much load transfer goes through the springs/dampers vs. the linkages directly.
  • Roll axis — the line between front and rear roll centres. The car doesn't physically rotate around it; it's a reference for how force is distributed, not a real axle.
  • Instant centre — the virtual pivot point that governs wheel path and camber change through travel.

How to measure:

  • From CAD, or by physically measuring pickup point coordinates on the car
  • Validate with suspension displacement sensors or a K&C rig if available

Entered in Kinematics, which also runs a live Motion Analysis so you can sanity-check the resulting curves before using them in a full simulation.

Unsprung Mass

Unsprung mass (wheels, tyres, brakes, hubs, and the suspension components that move with them) sets the suspension's natural frequency, which affects both ride quality and how well the tyre tracks the road.

How to measure: weigh the components individually, or use load cells to measure the moving mass during a suspension displacement test.

Entered in Chassis.

Prioritizing Your Time

If you're working from incomplete data, get these right first — they have the largest effect on results:

  1. COG height and anti-roll bar stiffness — both feed directly into load transfer and balance
  2. Motion ratios — get suspension tuning acting the way you expect it to
  3. Suspension kinematics — everything else in the vehicle model builds on this geometry

Missing values elsewhere generally cost you correlation precision rather than breaking the simulation outright — see Kinematics for what happens when geometry is incomplete.

Once you have real telemetry, validate the model against it rather than trusting measurements alone — see Results Upload and Trace View.