OpenSpec Change: enterprise-gaming-vehicle-physics

Change ID: enterprise-gaming-vehicle-physics
Package: @suaveplan/vehicle-physics
Category: gaming/rigs
Target path: gaming/rigs/vehicle-physics
Status: PROPOSED
Date: 2026-04-24
Reference spec: /mnt/s/web/suaveplan/enterprise/vehicle-physics.md

Summary

Deliver @suaveplan/vehicle-physics on the genesis branch from scratch at enterprise quality. The package provides engine-agnostic vehicle physics using Pacejka Magic Formula tire model, spring-damper suspension per wheel, multi-wheel drivetrain (FWD/RWD/AWD), differential, braking, and aerodynamic drag. All math is pure TypeScript with no runtime deps — physics backends plug in via interface. Genesis adds Zod config schemas, structured errors, injectable clock, OTel telemetry, and property tests verifying tire force symmetry and suspension convergence.

Current-state audit (genesis)

Package does not exist on genesis yet — fresh build.

Available workspace deps on genesis

Package	Role
`@suaveplan/error` (`workspace:^`)	`VehiclePhysicsError`; `VEHICLE.*` codes
`@suaveplan/types` (`workspace:^`)	`Clock`
`@suaveplan/events` (`workspace:^`)	`vehicle:collision`, `vehicle:flip`, `vehicle:stall` events
`zod` (`catalog:forms`)	`VehicleConfig` schema
`@opentelemetry/api` (`catalog:observability`)	Step duration histogram

Public API surface

function createVehicle(config: VehicleConfig): Vehicle

interface VehicleConfig {
  mass: number
  wheelBase: number
  trackWidth: number
  centerOfMassY: number
  engine: EngineConfig
  transmission: TransmissionConfig
  wheels: WheelConfig[]
  aerodynamics?: AeroConfig
  backend?: VehiclePhysicsBackend
  clock?: Clock
}

interface EngineConfig {
  maxTorque: number           // Nm
  maxRpm: number
  torqueCurve?: [rpm: number, torque: number][]
  idleRpm?: number
}

interface TransmissionConfig {
  type: 'FWD' | 'RWD' | 'AWD'
  gearRatios: number[]
  finalDrive: number
  differentialSlip?: number
}

interface WheelConfig {
  position: Vec3
  radius: number
  suspensionRestLength: number
  suspensionStiffness: number
  suspensionDamping: number
  tireGripLateral: number
  tireGripLongitudinal: number
}

interface Vehicle {
  update(dt: number, input: VehicleInput): void
  teleport(position: Vec3, rotation: Quat): void
  applyImpulse(impulse: Vec3): void
  flip(): void
  readonly position: Vec3
  readonly rotation: Quat
  readonly velocity: Vec3
  readonly speed: number        // m/s
  readonly rpm: number
  readonly gear: number
  readonly wheelsGrounded: boolean[]
}

interface VehicleInput {
  throttle: number    // 0–1
  brake: number       // 0–1
  steering: number    // -1 to 1
  handbrake: boolean
  clutch?: number
}

Error codes

type VehicleErrorCode =
  | 'VEHICLE_INVALID_CONFIG'
  | 'VEHICLE_BACKEND_NOT_SET'
  | 'VEHICLE_UPDATE_FAILED'
  | 'VEHICLE_INVALID_GEAR'

New additions for genesis

Pacejka tire model — lateral and longitudinal force from slip angle / slip ratio; configurable B/C/D/E coefficients.
Automatic gear shifting — RPM-based shift logic with configurable up/down thresholds.
Aerodynamic drag + downforce — 0.5 * rho * Cd * A * v² drag; downforce scales with speed².
Suspension raycast — VehiclePhysicsBackend.castRay() for each wheel per tick; ground contact from hit distance.

File layout

gaming/rigs/vehicle-physics/
  package.json
  tsconfig.json
  vitest.config.ts
  src/
    index.ts
    error-codes.ts
    constants/index.ts
    types/common.ts
    types/common.md
    core/
      vehicle/
        vehicle.ts
        vehicle.md
        vehicle.types.ts
        vehicle.test.ts
        index.ts
    models/
      pacejka/
        pacejka.ts
        pacejka.md
        pacejka.test.ts
        index.ts
      suspension/
        suspension.ts
        suspension.md
        suspension.test.ts
        index.ts
      drivetrain/
        drivetrain.ts
        drivetrain.md
        drivetrain.test.ts
        index.ts
    backends/
      null-backend/
        null-backend.ts
        null-backend.md
        null-backend.test.ts
        index.ts
  tests/
    property.test.ts

Impact

Downstream: @suaveplan/r3f-vehicle wires this to Rapier. Prerequisites: @suaveplan/error, @suaveplan/types, @suaveplan/events.

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