sessions: document hyundai canfd steer torque bump
Reference for the 270->324 change in commit 4058269. Covers what each
constant means, the two-files-must-stay-in-lockstep rule, the path to
push higher (324 -> 384, the community-consensus safe ceiling), risks
and symptoms to watch for at higher values, verification steps, and
rollback procedure.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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# Session: 2026-04-26 — Hyundai CAN-FD steering torque bump
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Documentation for commit `4058269` on `clearpilot`. Reference for any
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future re-tuning.
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## What changed
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Bumped this Tucson HDA2 (CAN-FD platform) from comma's conservative
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steer ceiling to a value that gives more headroom on tighter on-ramp
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clovers, plus a small rate-limit nudge so the controller can actually
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reach the new ceiling within reasonable transient time.
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| Constant | Before (comma default for CAN-FD) | After (this commit) | Comma's non-CAN-FD HKG default |
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|---|---:|---:|---:|
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| `max_steer` / `STEER_MAX` | 270 | **324** | 384 |
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| `max_rate_up` / `STEER_DELTA_UP` | 2 | **3** | 3 |
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| `max_rate_down` / `STEER_DELTA_DOWN` | 3 | **5** | 7 |
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| `max_rt_delta` | 112 | **134** | ~150 |
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## Where the change lives — TWO files in lockstep
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The panda safety firmware enforces these limits **independently** of
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openpilot. If only one side is bumped, panda rejects the larger
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commands and you get cut-out / `commIssue` behavior. **Always change
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both, always to the same numbers, in the same commit.**
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1. **`panda/board/safety/safety_hyundai_canfd.h`** (lines 3-19)
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- `HYUNDAI_CANFD_STEERING_LIMITS` struct: `max_steer`, `max_rate_up`,
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`max_rate_down`, `max_rt_delta`.
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- This is C; modifying it changes the panda firmware hash, which
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forces an automatic re-flash on next `pandad` start. No manual
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panda flash command needed.
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2. **`selfdrive/car/hyundai/values.py`** (CAN-FD branch of
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`CarControllerParams.__init__`, lines 29-36)
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- `STEER_MAX`, `STEER_DELTA_UP`, `STEER_DELTA_DOWN`.
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- Pure Python; picked up on next `controlsd` start.
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## What each constant does
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- **`max_steer` / `STEER_MAX`** — peak torque magnitude the controller
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can request. Hard ceiling. Going past this is the headline "more
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torque" knob.
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- **`max_rate_up` / `STEER_DELTA_UP`** — per-100Hz-cycle upward slew
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cap. Higher = faster ramp into a turn. With `max_rate_up = 3` and
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`max_steer = 324`, time from 0 to ceiling is 324 / 3 = 108 cycles =
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1.08 s.
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- **`max_rate_down` / `STEER_DELTA_DOWN`** — per-cycle downward slew
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cap. Higher = faster release back toward straight. We chose 5 (vs
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comma's 7) for a smoother release feel.
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- **`max_rt_delta`** — cumulative torque change allowed across a
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rolling 250 ms window (`max_rt_interval`). It's a long-window
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envelope check, separate from the per-cycle rate. Should scale with
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`max_steer` — we used `max_steer × ~0.41` to mirror comma's ratio.
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- **`driver_torque_allowance` / `STEER_DRIVER_ALLOWANCE`** — driver
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wheel torque (Nm read off the wheel) that's tolerated before the
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system starts derating its own command. Left at 250.
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- **`driver_torque_factor` / `STEER_DRIVER_MULTIPLIER`** — how
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aggressively the system fights driver input above the allowance.
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Left at 2.
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## How to go higher (path to 384)
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`384` is the community-consensus safe ceiling for HKG. Comma uses it
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as the default for every non-CAN-FD HKG that isn't on the explicit
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255-blacklist, and they merged it for HDA1 CAN-FD (EV6 / Ioniq 5) in
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[openpilot PR #25723](https://github.com/commaai/openpilot/pull/25723).
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The PR author noted "max steer needed to be 384 to make basic turns."
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Tucson NX4 HDA2 is **not** on the 255-blacklist (see
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[issue #24122](https://github.com/commaai/openpilot/issues/24122) for
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the verified blacklist).
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To go from 324 → 384:
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```c
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// panda/board/safety/safety_hyundai_canfd.h
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.max_steer = 384,
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.max_rt_delta = 158, // ~max_steer × 0.41
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.max_rate_up = 3,
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.max_rate_down = 5, // or 7 for comma-matched aggressive release
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```
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```python
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# selfdrive/car/hyundai/values.py CAN-FD branch
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self.STEER_MAX = 384
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self.STEER_DELTA_UP = 3
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self.STEER_DELTA_DOWN = 5 # or 7
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```
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Beyond 384 is uncharted for HKG — comma has not tested past it. Some
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forks (sunnypilot has discussions) try higher for very heavy vehicles
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but with mixed results. Don't go past 384 without an explicit reason.
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## Things to watch for / community-flagged risks at higher values
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1. **EPS time-out cut every ~90 frames.** The CAN-FD safety already
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forces a brief torque cut to stop the EPS from faulting (the
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`min_valid_request_frames = 89`, `max_invalid_request_frames = 2`,
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`min_valid_request_rt_interval = 810000` block of
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`HYUNDAI_CANFD_STEERING_LIMITS`). This is independent of
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`max_steer`. Bumping the ceiling does not lengthen the cut-free
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window — you just hold the higher torque for the same ~890 ms before
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the brief cut. If you're getting `Steering Temporarily Unavailable`
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*during sustained turns*, the issue is this cut, not the ceiling,
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and it can't be tuned without risking a real EPS fault.
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2. **`steerTempUnavailable` / "Cruise Fault: Restart the Car".** Has
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been reported on cars in the 255-blacklist when pushed to 384.
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Tucson NX4 is not blacklisted, so 324–384 is normally safe — but if
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you see this alert during slow sweeping turns, that's the symptom.
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Roll back to 270 and confirm.
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3. **Lateral accel retune.** Higher torque headroom can cause the
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torque controller to overshoot if `latAccelFactor` was tuned for
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the old ceiling. EV6/Ioniq 5 testing in PR #25723 had to drop
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lateral accel to 2.5 m/s² when bumping from 270 to 384. Watch for
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over-correction (zig-zag in lane center) after a bump and retune
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`latAccelFactor` in `selfdrive/locationd/torqued.py` or via the
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torque-tune Params if needed.
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4. **Driver-fight feel.** `driver_torque_allowance = 250` /
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`driver_torque_factor = 2` is the blending knob. Most "openpilot
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fights my hands" complaints come from people who lowered allowance
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or raised factor. Don't touch these without a specific reason.
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5. **Panda safety hash mismatch.** Changing
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`safety_hyundai_canfd.h` regenerates the panda firmware binary with
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a different signed hash. On the next `pandad` start, pandad detects
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the mismatch and re-flashes the panda automatically (see
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`pandad.log`: "Panda firmware out of date" → "flash: flashing" →
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"Done flashing"). Takes ~10 s. No manual action needed; just expect
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a brief delay before controls come up.
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## Verifying the change took effect
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```bash
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# 1. Confirm the rebuild happened and panda firmware was re-signed.
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grep "panda/board/obj/panda_h7" /tmp/build_only.log 2>/dev/null # or run build_only.sh and watch for "signing N bytes"
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# 2. Watch for re-flash on launch.
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tail -f /data/log2/current/pandad.log
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# Should see: "Panda firmware out of date, update required"
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# "flash: flashing"
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# "Done flashing"
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# 3. Confirm the openpilot side is using the new value.
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su - comma -c 'PYTHONPATH=/data/openpilot python3 -c "
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from cereal import car
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from openpilot.common.params import Params
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cp_bytes = Params().get(\"CarParams\")
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with car.CarParams.from_bytes(cp_bytes) as cp:
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print(\"safetyConfig safetyParam:\", [c.safetyParam for c in cp.safetyConfigs])
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"'
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# 4. Live-check the actual commanded torque ceiling (drive a moderate turn).
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# carControl.actuators.steer should now be able to peak above 0.79 (270/255 normalized)
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# but stay under 1.0 (full saturation at the new ceiling).
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```
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## Rollback
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If anything misbehaves, revert just the two-file commit:
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```bash
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git revert 4058269
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chown -R comma:comma /data/openpilot
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su - comma -c "bash /data/openpilot/build_only.sh"
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# Next pandad launch will re-flash back to 270.
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```
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## Sources
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- [openpilot PR #25723 — HDA1 EV6/Ioniq 5 270 → 384](https://github.com/commaai/openpilot/pull/25723)
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- [openpilot issue #24122 — HKG torque blacklist verification](https://github.com/commaai/openpilot/issues/24122)
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- [openpilot PR #26427 — Hyundai Tucson 2023 support](https://github.com/commaai/openpilot/pull/26427)
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- [sunnypilot — increasing torque help](https://community.sunnypilot.ai/t/increasing-torque-help-needed/2082)
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- [sunnypilot — raising torque for heavier vehicles](https://community.sunnypilot.ai/t/raising-the-torque-for-heavier-vehicles/862)
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