# VehicleBase reference

VehiclePhysics.VehicleBase is the base class for all the vehicles. Derived classes implement the engine's internal parts by instancing and connecting Block classes (engine, gearbox, etc).

## VehicleBase overrides

#### OnInitialize

Configure the number of wheels by calling SetNumberOfWheels(n). Then create, configure and connect all your blocks. Use the Block.Connect method.

Wheels can be accessed via wheels[n] and wheelsState[n] after calling SetNumberOfWheels:

"wheels" are the actual Wheel blocks. Required settings:

• mass
• tireFriction

"wheelsState" are the meaningful values of the wheels. Required settings:

• wheelCol
• steerable

Important: you must configure each WheelState with the corresponding the WheelCollider WheelState.wheelCol. Also, ensure to flag the steering wheels as steerable (this is used by the force feedback calculations).

#### OnPreDynamicsStep

Optional: For advanced / highly specialized use.

Invoked before computing each dynamics step. Common vehicle controllers don't need to override this.

#### DoExternalSuspensionForce

Optional: Set up WheelState.externalUpForce (Newtons) and externalUpForceFactor.

Used for implementing advanced suspension parts such as anti-roll bars.

#### DoUpdateBlocks

Update the inputs and states for your blocks: engine, brakes, gear, etc. Called before each integration step (FixedUpdate rate).

#### DoUpdateData

Populate the data bus with the actual values of the vehicle. Called after each integration step (FixedUpdate rate).

#### OnUpdate

Called at the start of Update. Adjust visual and per-frame stuff here (Update rate). Frames may be skipped here.

Do NOT override the standard Update, FixedUpdate, or LateUpdate in the derived classes.

#### GetInternalObject

Optional: Allow the vehicle to expose references to internal classes / blocks on demand. Each VehicleBase implementation chooses which items to expose.

This is intended for debugging / monitoring / telemetry the internal values that don't make sense to expose otherwise.

Some of these settings are likely to be changed or moved in upcoming versions. Most important are described here.

#### Tire side deflection

Spring rate for the tire side to deflect and bend when sliding laterally. It can be used to simulate tires targeted to different speeds. Tires with low rates (8-20) may become difficult to drive at high speeds.

This setting will be moved to Tire Friction at some point

#### Tire impulse ratio

The default value of 0.5 works correctly on most vehicles.

• It can be raised on vehicles with low center of mass (F1 and racing cars) for enhancing the effect of the transition from slip to adherent.
• It should be lowered on vehicles with elevated center of mass if they experiment visible instabilities at rest.

Tech details

The VPP solver calculates the impulses that keep the tires adherent to the surface. These are the ideal impulses for the same vertical level as the center of mass. Tire forces are applied at a different vertical level (contact points), so these forces induce a torque in the vehicle as side effect. This torque can lead to numerical instabilities in the tire forces, being bigger with the vertical distance from the contact points to the center of mass. The tire impulse ratio prevents this effect by multiplying the calculated impulse before being applied to the vehicle as tire force.

#### Wheel sleep velocity

Wheels moving slower than this speed are allowed to sleep when no other forces / torques that can move them are present.

#### Integration steps and method

Substeps are subdivisions of the Unity physics time steps that are used for calculating the internal torques, forces and momentums at every block in the vehicle. The more substeps, the more precise are the numeric results but CPU usage is increased.

A minimum value of 2 substeps is recommended. Multi-driven-axle vehicles should configure at least two substeps per driven axle.

Detailed information: Solver substeps explained

#### Engine reaction factor

Advanced: ratio of the reaction torque used at the engine torque calculations.

Reducing this ratio solves the low-frequency numerical resonances among wheels and engine that may occur at high-torque situations (i.e. heavy vehicles in slow gears). It should always be 1.0 unless this effect i