Lateral tire grip and braking budget — actual Unreal source QA¶
Status: new Unreal source integration; not an UE5.8-compiled, packaged, installed or calibrated playable racing game. The single chassis and four attached cosmetic wheel cylinders remain a rigid-body prototype.
Why this change matters in the actual race¶
The previously merged braking model imposes a plausible approximate
longitudinal deceleration limit. The lateral anti-slide model was still
applying mass × sideways speed × 8.5/s (Arcade baseline), with just
a frame-dependent reversal clamp. In a high-speed physical slide this
could request far more than 1 g sideways force even if the tires
were already using their available grip to brake. That is not
convincing racing-car behavior.
The real ALatebrakeCarPawn::Tick now uses
latebrake::CalculateLateralGripForce to apply an actual Chaos
body-right force opposite the measured chassis lateral velocity,
for both the player and the single autonomous rival.
- The requested correction begins with the existing handbrake drive profile's base lateral response, scaled once by garage grip, observed tire condition, confirmed off-pavement status and actual collision damage. Upgrades cannot accidentally multiply twice.
- The force is capped by provisional lateral acceleration allowances of 1250 cm/s² Arcade and 1050 cm/s² Simulation Inspired, further scaled by qualified effective grip. Higher lateral velocity cannot authorize an arbitrarily larger contact force.
- Braking and lateral correction share a heuristic combined grip
envelope (1550/1350 cm/s² per handling mode, before condition).
The controller takes the same-frame, already bounded real
braking demand from
GripLimitedBraking, not an estimated pedal value. More committed braking can leave less lateral authority for maintaining a racing line. - Human-only handbrake engagement reduces lateral grip to 42% of the otherwise available budget. It maintains separate lower longitudinal handbrake deceleration without giving the rival a human-controlled handbrake.
- Force sign follows actual physical body-right movement (including both sides of a slide), and a single qualified frame cannot remove more than 80% of the measured lateral speed with this extra force. Invalid force inputs neutralize the driving tick before propulsion.
- This does not rewrite velocity, rotate the actor kinematically, reset race checkpoints, grant wins/credits, change saves or bypass the existing Chaos contact/physical-speed readiness checks.
No real tires have been implemented. This is a finite-grip arcade approximation. It does not simulate individual tire contact patches, suspension, normal loads, dynamic weight transfer, combined slip angles at individual wheels, an ABS system, wheel torque, or real-world manufacturer handling data.
Validation in source CI¶
Tests/Standalone/LateralGripBudgetTests.cppruns under strict C++20 compilers on Windows, Linux and macOS. It validates mild and saturated slip, mirrored sideways direction, reverse-side correction, off-road grip, garage-tuned grip, Simulation handling, handbrake drift, simultaneous braking/cornering, fully spent grip, frame hitches, nonfinite physics and 20,000 varied samples.Tests/Editor/UnrealLateralGripBindingTests.pyconfirms the actual shared physical pawn consumes real velocity/mass plus previously qualified brake/heat/surface/tire/damage state, and that score/save and actor-teleport authority is unchanged.- Existing lateral/handbrake/source-composition contract tests now reject reintroduction of the excessive linear sideways damping force.
Real Win64 acceptance required before calling this playable¶
- Use the manual authorized UE 5.8/UHT compile and cook pipeline; drive an installed candidate with actual chassis physics, not C++ tests or the separate 2D experimental preview.
- At 30, 60, 100, 150 km/h, record transient steering/slalom behavior, measured lateral G, sustained turning radius and speed loss. Compare 30/60/120 FPS and uneven frame pacing.
- Enter a deliberate handbrake slide and countersteer both directions. Confirm it doesn't instantly cancel slip or become uncontrollable; measure how quickly traction returns on release.
- Brake heavily while turning on pavement, then after confirmed off-pavement entry. Confirm lateral authority diminishes without kinematic teleportation or force impulses.
- Repeat with all six garage selections, both handling modes, fresh/worn tires, collision damage, pit replacement, nitro, rival AI cornering and engine heat, including reverse.
- Verify no regression to race clock, directional gates, active rival completion, career medals, profiles or actual package logs.
Numbers are starting hypotheses, not measured or certified. They must be tuned on a genuine installed game and replaced with proper original vehicle skeletal meshes and Chaos wheel/suspension models before a simulation-quality release. See [playable release gate