Configuring Realistic Vehicles
This is a checklist of technical specifications you would need out of a real vehicle for mapping it to Vehicle Physics Pro.
Some values are not widely available, but they may be estimated out of other specs and performance data.
- Useful resources:
- Cars-Data (weights, sizes, transmission...)
RRI Powertrain Performance Graphs (engine dyno curves)
Mass and center of mass (CoM)
- Total vehicle weight.
- Weight distribution, as tested, front/rear (weight per axle).
- Height of the center of mass. Not typically available, but can be guessed to be around the top part of the chassis. It can also be deducted from the angle the vehicle could drive on two side wheels.
Engine, transmission and driveline
- Engine torque and power. Ideally, a "dyno" curve if available. The curve shape also helps configuring the engine brake.
- Engine rev up/down time. How fast the engine revs up when fully pressing throttle at neutral gear, and how much time takes it to rev down to idle after releasing throttle. These data can be used for estimating the engine inertia and the engine brake curve.
- Drive information: front (FWD), rear (RWD), all (AWD), combined (details?)...
- Transmission type: manual, automatic, manual with auto shift, automatic with manual shift.
- Number of gears and their ratios.
- Final drive ratio (typically specified by the differential).
- Differential type and ratio if available.
Other elements may be present in the driveline, specially in AWD or dynamic-drive setups. Examples: center transfer case, asymmetric (epicyclic) differential, torque splitter (haldex)...
Wheels and suspension
Detailed suspension specifications aren't typically available. They may be deducted/adapted by watching videos where the vehicle is tested under stress conditions.
- Wheel radius.
- Front to rear axle distance (wheelbase).
- Left to right distances (track front, track rear).
- Vertical position of the wheel either when suspension is fully compressed, or given a known suspension compression. This will define the anchor of the suspension.
- Suspension distance.
- Suspension spring rates.
- Suspension damper rates.
Use the default values as starting point. You can fine tune them later using information from the real vehicle, if available:
- Maximum acceleration and/or brake distance without wheel lock can be used for calculating the peak tire friction.
- Brake distance with locked wheels can be used for calculating the asymptote tire friction.
- Maximum steer angles in curves without tire sliding at a given speed can be used for configuring the slip points for the peak friction.
A precise configuration requires comparing the real reactions of the vehicle in different situations and fitting the tire friction parameters in the simulation for matching them.
Ideally, the best tire friction data is the one extracted from real tires (example). The resulting forces divided by the normal load result in the coefficient of friction under each situation.
- The aerodynamic drag can be estimated from the top speed.
- The aerodynamic downforce and tire sideways friction can be estimated from the maximum speed at a curve of known radius, and also from the maximum lateral G supported in curves.