Reference
Units and conventions
Review default 4ACE units, sign conventions, coordinate-frame notes, and analysis unit behavior.
Use this reference when entering SIM setup values, importing circuit or Driver Input data, defining design spaces, or reading analysis channels.
4ACE shows units beside many product fields and analysis channels. When a value has no physical unit, the product may show a blank unit. These docs use n/a when no unit applies or when a unit, default, or range has not been verified.
Default units by workflow
| Workflow area | Common fields | Default units shown in current docs or product metadata |
|---|---|---|
| Ambients | Air temperature, pressure, humidity, wind, track temperature, track global grip | °C, Pa, %, m/s, °, n/a |
| Drivers | Throttle, brake, brake force, steering rate, shift interval | %/s, N, °/s, s |
| Circuits | Start angle, distance channels, map position | °, m |
| Driver Inputs | Segment time, throttle, brake, steer angle, gear | s, %, °, n/a |
| FastSim and OpenSim settings | Step time, export rate, start velocity, start gear, duration, start position | s, Hz, km/h, n/a, m |
| Vehicle setup | Dimensions, masses, inertia, forces, stiffness, damping, pressure, temperature, speed, torque, power | mm, kg, kgm², N, N/m, N/mm, Ns/mm, Pa, °C, m/s, Nm, W |
| Analysis telemetry | Time, distance, speed, acceleration, angle, angular rate, force, torque, pressure, fuel, engine speed | s, m, m/s, m/s², deg, deg/s, N, Nm, Pa, kg, rpm |
| Batch Simulations | Parameter scenarios and generated designs | Uses unit from selected ambient or vehicle parameter |
Unit reference
| Unit | Meaning | Common use |
|---|---|---|
% | Percent | Throttle, brake, humidity, brake distribution, slip ratio. |
%/s | Percent per second | Driver throttle-rate and brake-rate limits. |
° or deg | Degrees | Setup fields and telemetry angles. Product metadata uses both symbols depending on source. |
°/s or deg/s | Degrees per second | Driver steering-rate limits and telemetry angular rates. |
°/mm | Degrees per millimeter | Steering and suspension polynomial coefficients tied to travel. |
°/° | Degrees per degree | Camber change versus steer angle. |
Hz | Samples per second | Simulation telemetry export rate. |
J/kg | Joules per kilogram | Fuel heat value. |
kg | Kilograms | Mass, corner weight, fuel load, fuel used. |
kgm² | Kilogram square metres | Inertia tensor terms. |
km/h | Kilometres per hour | Simulation start velocity. |
m | Metres | Distance, lap distance, start position, track-map position. |
m/s | Metres per second | Vehicle speed, wind speed, telemetry velocity. |
m/s² | Metres per second squared | Telemetry acceleration. |
m² | Square metres | Aerodynamic frontal area. |
mm | Millimetres | Vehicle setup distances, ride heights, rack travel, tire radius. |
mm/s | Millimetres per second | Suspension travel velocity. |
mm² | Square millimetres | Brake master-cylinder and caliper-piston areas. |
mm/(m/s) | Millimetres per metre per second | Tire radial expansion versus forward speed. |
N | Newtons | Forces, brake force, preload, aero force, tire load. |
N/m | Newtons per metre | Body ground-contact vertical stiffness. |
N/mm | Newtons per millimetre | Spring, anti-roll bar, bump rubber, rebound stop, and tire stiffness. |
Nm | Newton metres | Engine, brake, drive, gearbox, and differential torque. |
Ns/mm | Newton seconds per millimetre | Damper and tire damping rates. |
Pa | Pascals | Air pressure, brake pressure, intake pressure. |
Pa/(m/s) | Pascals per metre per second | Engine intake-pressure polynomial versus vehicle speed. |
rpm | Revolutions per minute | Engine speed, gearbox speed, differential speed. |
s | Seconds | Time, lap time, simulation duration, segment times, shift intervals. |
W | Watts | Engine power offset. |
n/a | No physical unit or not verified | Gear numbers, coefficients, ratios, gains, selectors, and fields where no unit is shown. |
Sign and orientation conventions
| Convention | Meaning | Where it appears |
|---|---|---|
Aerodynamic drag coefficient Cd | Cd is positive in current aerodynamic parameter text. | Aerodynamics submodule, lookup tables, polynomials. |
Aerodynamic lift coefficients Clf and Clr | Positive value means less load on that axle as speed increases. Downforce uses a negative coefficient. | Aerodynamics submodule. |
| Wind direction | 0° means headwind at lap start. Angle increases clockwise when the track is viewed from above. | Ambient wind direction. |
| Start angle | Circuit map rotation is a whole number from -180 to 180. | Circuit import and circuit fields. |
| Steering rack travel | Positive rack travel is to the left. | Steering submodule. |
| Steering wheel angle | Positive steering wheel angle turns counter-clockwise. | Steering submodule. |
| Wheel steer angle | Positive steer angle is counter-clockwise when the wheel is viewed from above. | Steering submodule and Driver Inputs. |
| Camber angle | Positive camber means the top of the wheel is farther from the car center than the bottom. | Steering, suspension, tires. |
| Toe angle | Positive toe means the front of the wheel is closer to the car center than the rear, which is toe-in. | Suspension setup and kinematics. |
| Wheel travel | Positive wheel travel means rebound. | Suspension motion-ratio and kinematics rows. |
| Spring or damper travel | Positive spring or damper travel means elongation in the relevant motion-ratio row. | Suspension spring and damper rows. |
| Front view swing arm angle | Positive angle means the virtual line points upward from the tire contact patch toward the car. | Suspension kinematics. |
| Gear ratio | Ratio above 1 means input speed is higher than output speed. | Drivetrain gearbox, drop gear, and final drive rows. |
| Drive ratio front | 1 means front-wheel drive, 0 means rear-wheel drive, and values between mean all-wheel drive. | Drivetrain drive split. |
| Delta Time channel | Distance x-axis shows time delta in seconds. Time x-axis shows distance delta in metres. | Detailed Analysis. |
Coordinate-frame notes
Current user-facing sources verify rotational axis names for body inertia:
| Axis | Rotation name | Example use |
|---|---|---|
| X | Roll | Ixx inertia around x-axis. |
| Y | Pitch | Iyy inertia around y-axis. |
| Z | Yaw | Izz inertia around z-axis. |
Some coordinate fields, such as sprung mass center of gravity and ground-clearance points, refer to the vehicle coordinate system. The current source used for this page does not define positive X, Y, or Z translation direction. Confirm the source data convention before assigning signs to those coordinates.