# VehicleDrivetrain

> Talos 0.7 · Since 0.6

## Fields

| Field | Type | Required | Default | Allowed values | Description |
|---|---|---|---|---|---|
| `engine` | `VehicleEngine` | no |  |  |  |
| `gears` | `number[]` | no |  |  | Forward gear ratios, first gear first, each greater than zero and strictly descending. Wheel torque is engine torque times the gear times finalDrive. An override REPLACES this array whole. |
| `reverseGear` | `number` | no |  |  | Reverse gear ratio, a positive number like the forward gears. The direction is the solver's, not a sign here — writing a negative ratio is a `vehicle-invalid` violation, not a reverse gear. |
| `finalDrive` | `number` | no |  |  | Differential ratio multiplying every gear, greater than zero. Typically 3..4.5. |
| `differential` | `VehicleDifferential` | no |  | `open`, `locked`, `lsd` |  |
| `shift` | `VehicleShift` | no |  | `auto`, `manual` |  |
| `shiftUpRpm` | `number` | no | `0` |  | Engine speed in rpm at which an automatic gearbox changes up, greater than zero and not above redlineRpm. Defaults to 0.9 x redlineRpm, so an engine that says nothing shifts just short of the limiter. Shifting earlier is what makes a van or a diesel feel like one. Ignored when `shift` is `manual`. |
| `shiftDownRpm` | `number` | no | `1` |  | Engine speed in rpm at which an automatic gearbox changes down, greater than zero and not below idleRpm. Defaults to 1.6 x idleRpm. It must sit below shiftUpRpm in the next gear up or the box hunts. Ignored when `shift` is `manual`. |
| `shiftTime` | `number` | no | `0` |  | Seconds the gearbox spends with no drive while it changes gear, zero or more. Defaults to 0.25. 0 is an instant shift, which is what an arcade vehicle usually wants; a torque-converter automatic is nearer 0.5. |

## See also

- `VehicleEngine`
- `VehicleDifferential`
- `VehicleShift`