Vehicle Configuration Guide #

This guide assumes you have your vehicle working according to the Creating a Vehicle section.

If you're modifying the values in runtime in the Editor, remember to backup your values before exiting Play mode. Either note them down to paper, or use the Copy Component / Paste Component Values options in the component's context menu.



Mass #

Configure the vehicle's mass in its Rigidbody component.

Vehicle mass

This mass represents the total mass of the vehicle in driving conditions as if we put it on a scale, including driver, passengers, fuel, wheels, cargo, etc.

Center of Mass #

Add a GameObject to the vehicle and name it CoM. Configure it in VPVehicleController > Center Of Mass.

Center Of Mass

Longitudinal position of the CoM (Z):

Vertical position of the CoM (Y):

The sideways position of the CoM (X) should be 0 (middle of the vehicle).

After configuring the CoM you may need to make adjustments to the suspension for accommodating the new weight distribution. Typically:

Inertia #

Inertia plays a critical role in the handling of the vehicle. Configure the inertia in the section Inertia of VPVehicleController.

Inertia

As initial configuration:

More details and information on configuring the Inertia: Inertia Helper

Suspension #

The suspension is configured per-wheel at the VPWheelCollider components.

Suspension

The suspension distance (m) should be configured for matching the vehicle's specifications. If these aren't available, try to figure out the complete travel distance of the suspension based on observations in the real vehicle.

The anchor (%) simply defines how much the suspension is currently compressed in the 3D model.

You can monitor the compression of the suspension in real time in the Telemetry window (VPTelemetry component) Susp column.

Warning

The compression values as shown in the Telemetry should never reach 1.0 or adverse physics effects may occur. This is by PhysX design/bugs and there's nothing we or Unity can do.

Springs and dampers #

The VPWheelCollider component includes an option to configure both spring and damper using the vehicle's mass, the number of wheels and the suspension distances:

VP WheelCollider context menu

Springs sustain the weight of the vehicle. A good starting point is configuring the spring rate (N/m) so each suspension can support up to twice of the distributed weight. Thus, if the weight is evenly distributed then each suspension would be at half of its travel at rest.

The rule of thumb for the spring rate is:

    Spring Rate = vehicle mass / number of wheels * 2 * 9.81 / suspension distance

You can always use real spring rates or any other values that fit better with your vehicle.

Dampers (or shock absorbers) limit the suspension movement and damp the spring oscillations. The damper setup affects the angular momentum of the vehicle on weight shifting situations (accelerating, braking, cornering...).

The damper rate (N/ms-1) should be configured so the oscillating behavior resembles the real vehicle.

The rule of thumb is for the damper rate is:

    Damper Rate = Spring Rate / 20

You may use a VPResetVehicle component to drop the vehicle from some height (Enter key), then observe how the suspension oscillates. Configure the damper rates until the result looks good enough for your vehicle.

Engine #

Engine

The engine torque curve is the sum of two curves: ideal torque curve (dotted orange) and friction torque curve (red). The result of adding those curves together is the final engine torque curve (green). When you watch at a dyno torque curve you're really watching this green curve.

The final torque curve (green) is guaranteed to cross three key values:

The Curve Bias parameters have some influence in the transitions between Idle and Peak.

The inertia defines how much "effort" takes to modify the rpm in the engine. Formula 1 style engines have very little inertia (0.1-0.2), while trucks have a large inertia in their engines (8-10). Standard cars are around 0.3 and 1.

The Engine Friction (red curve) produces the engine brake effect when no throttle is applied. It's defined by a base Torque (Nm) and two coefficients of friction, Rotational () and Viscous (). The effect of these parameters can be lively observed in the graph.

Torque Cap clamps the torque curve (green) with the given value. This simulates an electronically imposed torque limit.

Rpm Limiter limits the rpm the engine can reach.

The Idle Control configures the extra torque required to keep the engine running. Also provides smooth throttle values near the idle rpm (dotted white curve).

If the engine Can Stall the parameters can be configured as well:

Pro-Tip

The Starter Reliability can be used to simulate external factors such as drained batteries, cold temperatures, mechanical failures, and so on.

Pro-Tip

As happens in reality, a stalled engine can also be restarted inertially. That is leaving the vehicle running down a slope in neutral, then engaging a gear and releasing the clutch.

Clutch #

There are two main types of clutch in VPP:

Friction Disc

A disc plate clutch typically used in cars with Manual transmission, where the clutch is operated via clutch pedal.

Friction Disc Clutch

Max Torque Transfer defines the maximum amount of torque that can pass trough the clutch. A good value is around 1.5 times the maximum torque the engine can produce (Max Torque in the Engine's specifications).

Torque Converter

A fluid coupling device typically used in cars with Automatic transmission.

Torque Converter

Lock Rpm is the engine rpm where the torque converter produces a full lock. A good value produces a lock ratio at idle around 6-10% (Lock ratio @ idle in the inspector).

Pro-Tip: Automatic clutch in Manual Transmissions

The Torque Converter may also be used with the Manual Transmission. This effectively provides an automatic clutch in cars with manual transmission, which is great for the gameplay when the car is controlled via keyboard, gamepad, or devices without clutch pedal.

Transmission #

The transmission is configured in the Gearbox section.

Transmission

The Transmission type can be either manual or automatic:

Transmission Types

Manual

Gears are engaged individually, with a minimum interval among each change (Gear change time (s)).

  • Auto shift is also available in Manual transmissions.
  • Both clutch types (clutch and torque converter) are well supported in Manual Transmissions.
Automatic

Gears are progressively engaged, with a smooth transition in both torque and rpm among each gear.

  • Each gear change takes Gear transition time (s) to shift from a gear to another.
  • A minimum of Shift interval (s) time is enforced between two consecutive gear shifts.
  • Automatic transmissions should use a Torque Converter instead of a standard clutch.

The Gear Ratios define the power ratio that is applied to the engine torque. If the first gear ratio is 3.84, this means that the torque at the output of the gearbox in first gear will be 3.84 times the torque applied by the engine. The rotational velocity will be 3.84 times slower as well.

Any number of gears and ratios can be configured for both forward and reverse gears. Standard cars typically have 4 - 6 gears. Trucks can have 12, 18 or even more.

Requirements for gear ratios are:

In order not to change gear up if the drive wheels have lost their traction, the Auto shift mode only engages the 2nd gear if the vehicle's speed is above the 2nd gear min speed (m/s) value.

The Park mode is characteristic of the Automatic transmissions, but it can be simulated in Manual transmissions as well (Allow Park mode).

Driveline #

Configure which axle(s) from the Axles section are driven and the transmission devices between the gearbox and the drive wheels.

Driveline

More information on the differential types: Differential Block.

More information on the driveline configurations: Driveline Helper.

Tires #

Tire friction defines the grip of the wheels based on how much they are slipping.

Examples:

More information: Tire block

Steering #

Configure the Maximum Steer Angle for the steering wheels.

Enabling Ackerman requires a reference Transform in the vehicle:

Steering and Ackerman

This provides the standard Ackerman geometry. You may tweak it further by modifying the longitudinal position of the Ackerman reference:

Brakes #

Brakes

Good values for Max Brake Torque and Brake Bias (or Brake Balance) may be configured like this:

Repeat until finding a value of Max Brake Torque where only front or rear wheels lock, but not both. Then:

Repeat until finding a value of Brake Bias where both front and rear wheels lock again.

Repeat the first procedure to refine the Max Brake Torque value. The final value should lock all wheels.

More information on brakes and ABS: Brakes Helper

Driving Assists #

Steering Aids #

Enable Steering Limit in Sport mode. The movement of the steering wheel is then constrained to the range where the front tires can apply the maximum sideways grip.

Steering Aids

Rear drive (RWD) cars may experience a lot of oversteering at this point because rear wheels are heavily pushing and losing sideways grip. You may want to enable Traction Control (TCS) immediately afterwards (see below).

You may also enable Steering Help and configure Priority to either Go Straight or Drifting for simplified control and enhanced gameplay with keyboard / gamepad.

More information: Driving Aids Explained

Safety Aids #

Default parameters are a good starting point in all these.

Info

Safety aids may trigger frequently when testing the car with keyboard or gamepad. This is normal, as you're pushing the car to its limits constantly (full throttle, full steer, full brakes).

Still, this gives you hints on where the setup should be improved. For example, ECS triggers on oversteer and understeer. You may improve these behaviors by configuring suspension to reduce the chances of the ECS to activate.

Anti-Lock Braking (ABS) reduces brake pressure dynamically to prevent wheels to lock while braking.

Anti-lock Braking System (ABS)

Traction Control (TCS) in Sport mode limits throttle when drive wheels slip to ensure they provide the maximum traction.

Traction Control System (TCS)

Hints for minimizing the activation of the TCS

  • Use the TCS Custom Slip mode with a value slightly beyond the tire's peak slip.
  • Use a locking differential, or configure stiffer parameters for it.
  • Configure stiffer suspension in the opposite axle. I.e. stiffer front suspension and/or front anti-roll bar in RWD cars. Use real-world techniques here.
  • In manual transmissions with Disc Friction clutch: reduce the Torque Transfer value, so the clutch is allowed to slip slightly when switching gears.

Stability Control (ESC) selectively applies individual brakes to specific wheels to compensate understeering / oversteering.

Electronic Stability Control (ESC)

Hints for minimizing the activation of the ECS

  • Configure the ECS parameters to better fit the behavior of the vehicle. Use the Stability Control (ESC) section in the Telemetry window.
  • Tweak the suspension to reduce the grip at the part that doesn't slide. I.e. if the car understeers (front wheels slide), a stiffer rear suspension should reduce the rear grip providing a better front-rear grip balance. Use real-world techniques here.
  • Tweak the Inertia Bias parameter in the Inertia section of VPVehicleController so it better fits the expected handling of the vehicle.

Anti-Spin Regulation (ASR) works at low speeds by applying brakes to one drive wheel when it loses traction, allowing the other wheel to gain more traction and pushing the vehicle.

Anti-Spin Regulation (ASR)

Add-on components #

If all the above is configured correctly then the car should be reasonably drivable at this point. That was configuring the main mechanical aspects and specifications of the vehicle.

Next part is configuring the vehicle dynamics and the handling. Most of it is made with add-on components.

Dynamics add-on components

Pro-Tip: Rule of thumb for tweaking car handling

  • Handling at low-mid speeds is mainly affected by suspension and inertia.
  • Handling at high speeds is mainly affected by aerodynamics.

You may apply real world techniques directly for configuring the car handling.

Rolling Friction #

VPRollingFriction produces drag in the wheels based on the force they're supporting. The default value is a good starting point. Rolling friction together with aerodynamics define the vehicle's top speed.

Rolling Friction

Anti-roll bars #

The VPAntiRollBar component links the left-right suspensions of an axle to reduce the body roll of the vehicle and allow the momentum to shift quickly. This improves the responsiveness of the vehicle when taking corners, of tweaking the car's balance in the turns.

Each VPAntiRollBar components instance affects a single axle specified by the Axle parameter. In standard cars 0 is the front axle and 1 is the rear axle.

You may configure a single anti-roll bar to the front or to the rear axle, or add anti-roll bars to both axles. The decision depends on how you feel the handling of the car. As rule of thumb:

Note that this is valid for the suspension stiffness as well (spring and dampers).

Anti-roll bars

Aerodynamics #

Aerodynamics

Drag Coefficient

Produces aerodynamic drag based on the speed squared. This value has the most influence in the top speed of the vehicle.

Theoretically, it's the aerodynamic coefficient of the car multiplied by the frontal area. A good value for standard cars is around 0.2-0.5.

In practice, you may drive the car in a long straight (VPP provides the prefab Flat straight 50 Km x 100 m) and tweak the value until the top speed matches the specifications.

Downforce Coefficient

Produces aerodynamic downforce based on the speed squared. This is typically provided by the shape of the car and any spoilers it may have.

A good value for typical cars is around 0.1-0.4. Sport cars use 0.4-0.9 depending on their aerodynamic pack.

You may configure the aerodynamic behavior at high speeds by moving the longitudinal position of the Aero GameObject:

Check out the Susp column in the Telemetry window (VPTelemetry component) to check out how the downforce is compressing the suspension, and which part of the car is being pushed further.

Warning: watch the suspension compression

Ensure compression values as shown in the Telemetry never reach 1.0 at high speeds. If the extra downforce caused by aerodynamics compresses the suspension beyond the limit then you need to increase the suspension spring rate at the affected wheels.

Advanced Tip: Front and Rear aerodynamics

If the car heavily relies on the aerodynamics (i.e. a formula racing car) then you may configure front and rear aerodynamics independently.

  • Use two GameObjects with an VPAeroSurface each.
  • Put them at the longitudinal positions of the front axle and the rear axle, respectively.
  • The vertical positions should be the middle of the height of the car the corresponding position.

You may then configure drag and downforce independently at each position.