Assetto Corsa RaceChrono Bridge

RaceChrono has support for Assetto Corsa, but Assetto Corsa cannot send GPS-correct coordinates, that's why this bridge is required. With its' help one can select real track in RaceChrono, record sessions and compare them to real racing sessions.

Idea

Idea is simple: read data from AC, find track GPS coordinates, map it to in-game coordinates and republish AC telemetry in the same format, but with correct GPS

Requirements

• .NET 10 SDK: winget install Microsoft.DotNet.SDK.10

RaceChrono setup

Add a RaceChrono DIY device using a TCP/IP connection:

• Host: the address printed as awaiting RaceChrono connection at ... by the bridge
• Port: Bridge:Port from appsettings.json (19996 by default)
• NMEA 0183: enabled (GPS position, speed and bearing)
• RC2/RC3: enabled (RPM, acceleration, gear and analog channels)

RPM uses RC3's fixed rpm/d1 (Digital 1/RPM) field. If the bridge dashboard shows a non-zero RPM but RaceChrono does not, verify that RC2/RC3 is enabled and select the RPM channel in the RaceChrono live screen or analysis view. If the dashboard also shows zero RPM, the value is not arriving from Assetto Corsa.

Assetto Corsa telemetry channels

The bridge reads Assetto Corsa's UDP remote telemetry (RTCarInfo) and, when it runs on the same machine as Assetto Corsa, also reads an opt-in shared-memory block (enabled with Games:AssettoCorsa:SameMachineWithAC, true in the shipped appsettings.json). The shared-memory reader unlocks channels that are not available over UDP. All channels below can be mapped to RaceChrono $RC3 slots (see next section).

From UDP (always available):

Channel	Meaning	Unit
SpeedKmh	vehicle speed	km/h
EngineRpm	engine speed	rpm
Gear	gear index (0=R, 1=N, 2=1st, …)	index
Gas	throttle	0..1
Brake	brake	0..1
Clutch	clutch (may be inverted via InvertClutch)	0..1

Latitude/Longitude/Altitude, PosNormalized, Slope, and LapTime/LastLap/BestLap/LapCount are also read from UDP and remain mappable, but they are no longer in the default mapping: GPS is sent losslessly via NMEA $GPRMC/$GPGGA, and RaceChrono computes lap timing itself.

From shared memory (requires SameMachineWithAC):

Channel	Meaning	Unit	Source field
SteerAngle	steering (left −, right +)	normalized, ~±1 at full lock	Physics.SteerAngle
Fuel	fuel level	litres	Physics.Fuel
FuelPercent	fuel remaining	%	Physics.Fuel / StaticInfo.MaxFuel
TyreTempFL / TyreTempFR / TyreTempRL / TyreTempRR	tyre core temps	°C	Physics.TyreCoreTemperature[0..3]
TyrePressureFL / TyrePressureFR / TyrePressureRL / TyrePressureRR	tyre pressures	psi	Physics.WheelsPressure[0..3]
BrakeTempFL / BrakeTempFR / BrakeTempRL / BrakeTempRR	brake temps	°C	Physics.BrakeTemp[0..3]
BrakeTempMax	hottest brake	°C	max of the four
Heading / Pitch / Roll	attitude	°	Physics.Heading / Physics.Pitch / Physics.Roll
(gyro)	angular velocity → RC3 gyrox/gyroy/gyroz	deg/s	Physics.LocalAngularVelocity[0..2]

Assetto Corsa shared-memory struct layout adapted from mdjarv/assettocorsasharedmemory under the MIT License.

Notes:

• Acceleration axes remain fixed (not remappable): xacc=AccGHorizontal (lateral), yacc=AccGVertical, zacc=AccGFrontal, all in G. The gyrox/gyroy/gyroz fields, previously always 0, are now filled from shared-memory angular velocity (Physics.LocalAngularVelocity, rad/s → deg/s) when SameMachineWithAC is on. This feeds RaceChrono's IMU fusion (orientation / lean angle); it does not change the NMEA sentences. Verified against live AC: LocalAngularVelocity [0]=pitch, [1]=yaw, [2]=roll — matching the x=lateral / y=vertical / z=longitudinal order (a left turn gives +gyroy); Heading/Pitch/Roll are radians.
• Not provided by Assetto Corsa at all: engine coolant/water temperature, oil temperature, and oil pressure are NOT provided by Assetto Corsa via UDP or shared memory, so they cannot be bridged.
• Packing: RaceChrono's equation engine (bit/byte extraction) applies only to OBD-II / CAN-Bus channels, NOT to RC3 line-protocol analog channels — so each RC3 analog slot carries a single value (no bit-packing). Because there are only 15 analog slots, per-corner brake temps are not in the default map (BrakeTempMax is used instead); full per-corner data would require the CAN-Bus BLE transport.
• $RC3 analog/digital fields are printed with 3 decimal places, so Latitude/Longitude placed in analog slots are low-precision.

Available in AC UDP but not yet bridged (would require extending the reader): per-wheel wheel speeds, slip ratio / tyre slip, tyre load, suspension height, CamberRad, and ABS/TC "in action" flags. (Steering is bridged — but from shared memory as SteerAngle, so it needs SameMachineWithAC; AC's UDP Steer field is not used.)

RC3 channel mapping

The slot→channel mapping is configurable in appsettings.json under Bridge:Rc3Channels. Mappable slots are d1, d2, and a1..a15. Each value must be one of the Channel names from the tables above — including the now-non-default GPS/lap-timing channels — and any channel can be mapped to any d1/d2/a1..a15 slot. None (or omitting the slot) outputs a constant 0. An unknown slot or channel name fails fast at startup. Omitting Rc3Channels entirely keeps the defaults shown.

Shared-memory channels (SteerAngle, Fuel, tyre/brake temps and pressures, attitude, gyro, …) output 0 unless Games:AssettoCorsa:SameMachineWithAC is true and Assetto Corsa is running on the same machine.

"Games": {
  "AssettoCorsa": { "SameMachineWithAC": true }
},
"Bridge": {
  "Port": 19996,
  "BindAddress": "0.0.0.0",
  "Rc3Channels": {
    "d1": "EngineRpm", "d2": "Gear",
    "a1": "SpeedKmh", "a2": "Gas", "a3": "Brake", "a4": "Clutch",
    "a5": "SteerAngle", "a6": "Fuel",
    "a7": "TyreTempFL", "a8": "TyreTempFR", "a9": "TyreTempRL", "a10": "TyreTempRR",
    "a11": "TyrePressureFL", "a12": "TyrePressureFR", "a13": "TyrePressureRL", "a14": "TyrePressureRR",
    "a15": "BrakeTempMax"
  }
}

Useful links

• RaceChrono forum thread "Assetto Corsa?"
• RaceChrono article "Tutorial: DIY devices"
• AC Socket Document
• AC forum thread "AC UDP Remote Telemetry"
• Assetto Corsa Remote Telemetry Client by @rickwest
• mdjarv/assettocorsasharedmemory — Assetto Corsa shared-memory struct layout adapted under the MIT License.
• Topograhic maps (useful to find height of a location)

TODO

• Wiki/Instruction how to use with screenshots
• Issues tab

CI

The workflow is in .github/workflows/ci.yml (named CI in Actions).

Creating a release

Releases are tag-based. After your changes are on master and CI is green, create and push a tag like:

git tag v0.1.0
git push origin v0.1.0

Pushing the tag triggers .github/workflows/release.yml, which builds + tests again and then creates a GitHub Release with:

• ACRCBridge.App-v0.1.0-linux-x64.tar.gz
• ACRCBridge.App-v0.1.0-linux-arm64.tar.gz
• ACRCBridge.App-v0.1.0-win-x64.zip
• ACRCBridge.App-v0.1.0-win-arm64.zip attached.