We have released RumiCar Simulator v7.7.0. The release notes below are also available on GitHub.
v7.7.0
Added an optional braking system to cars (precise v2 engine only; with the default, nothing changes at all). The real RumiCar brakes with the reverse torque of its drive motor alone, so until now an FR car locked only its rear wheels while the fronts kept rolling freely. Measured (full-scale, 40 m/s down to 2 m/s) the stopping distances are FR 138.97 m / FF 88.11 m / AWD 65.85 m — more than a factor of two apart for the same mass and tires, purely because of the drivetrain. Choosing the new four-wheel friction brakes spreads the same total braking force over four wheels with a front/rear split (60/40 by default, plus front-biased 75/25 and rear-biased 45/55), which cuts the FR stopping distance from 138.97 m to 63.40 m, a 54% reduction. AWD barely moves (0.2%) — motor braking already reaches all four wheels there, so this equipment matters for cars that have wheels receiving no braking at all. Lock-up emerges from the wheel rotation equation; there is no lock threshold anywhere in the code. Raising the front share 45% → 60% → 75% raises the front lock fraction monotonically 0.52 → 0.76 → 0.84 and lowers the rear one 0.68 → 0.36 → 0.00. In a straight line the three splits barely differ, because the braking command (4.013 g) is 2.87× the tire capacity (1.40 g) and every wheel saturates however you distribute it. The split matters in corners. Trail braking was measured over two independent grids (54 and 288 cells) sweeping radius, entry speed, brake duration, road μ and steering type. What can be claimed (1): an FR car’s rear always locks less (mean 0.800 → 0.210 and 0.662 → 0.123; not one of the 342 cells got worse). (2): an FR car’s recovery never degrades (cells returning to the corner went 13 → 39 and 88 → 200; 138 gained, 0 lost). (3): an FF car locks its rear more (0.000 → 0.320) — a motor-braked FF puts no braking on the rear at all, so spreading to four wheels necessarily increases it. This is not equipment that is always safer. What cannot be claimed: that peak sideslip falls. The mean does fall (FR 55.1° → 22.7°) but individual cells go the other way (9 of 54, 54 of 288), so it is recorded as a continuous measurement, not a law. ⚠ The effect changes sign with the regime — at full scale an FR car brakes 2.11× harder, but on the tabletop and mid-scale it is 0.77×, i.e. weaker. The cause is not the regime as such but the semi-implicit wheel ODE enabled there for speed: its damping uses a safe-side (over-large) tire stiffness, so less force reaches the road than was commanded (equally true of the default motor brake at 0.59 delivered/commanded; 0.43 once spread over four wheels). Where that path is not taken the ratio is 0.96–2.11, so any loss stays within 4%. FF and AWD cars lose recovery cells (over 288 cells FF 283→270, AWD 258→251); only FR never gets worse in a single cell. For drifting the effect was “loses speed, keeps robustness”. Re-running the standing drift re-examination gate with four-wheel friction brakes fitted, the trail-braking driver’s robustness (cells surviving a ±10% entry-speed error) did not drop: 14/24 → 15/24, but its speed advantage fell from 8/8 conditions to 3/8, and the single free-space window where drifting was faster closed (1/8 → 0/8). The cause is not that grip driving got faster (on dry it is bit-identical at 3.53 s → 3.53 s, and on low μ it got slightly worse) — the drifting side got slower in all 8 conditions, which confirms as a causal experiment the earlier conjecture that the trail-braking advantage rests on the FR rear-axle lock. Fit real brakes and the entry to that technique — breaking the rear loose by locking it — disappears. This is machine-checked by a standing gate (wf_av2_brake.mjs, 56 assertions) and a real-browser gate (28 checks); with the default motor brake the frozen benchmarks f0–f3, official-race verifyHash values and existing share URLs are all unchanged.
Verifying this release yourself
cd Simulator
node wf_run_all.mjs # the full assertion-gate suiteThe suite runs from a fresh clone with no dependencies beyond Node.js.
The real-browser checks under Simulator/browser/ additionally need npm install and a display.