TSUISO

TSUISO (追走 — "chase run") is a tandem drift battle on a night mountain pass, scored the way the real sport scores it: nobody times you, and getting past the car ahead earns nothing. An AI lead car throws itself down nine corners of a two-lane touge in one committed slide, and the judges pay you for how you follow.

How to play

• W throttle · S brake · A / D steer · SPACE handbrake. That is the whole car. Touch controls on mobile; press H or ? any time for the full list.
• Points only accrue while the rear is genuinely out — about 9° of slip and real speed. Straighten up and the meter stops.
• Fill the painted clipping zones while sideways for line bonuses.
• The twist is proximity. A live multiplier climbs from ×1 to ×3 as you close on the lead car's door while you are both in the drift. Door-to-door through the long sweeper is where whole medals are earned — and one twitch from a crash.
• Rubbing is racing: a light tap on the lead is a small deduction. A hard hit — or a hard meeting with the guardrail — ends the run on the spot. A spin zeroes the corner and resets the multiplier to ×1.

All three real initiations work from the keyboard: power-over, a handbrake flick, and the Scandinavian feint.

The physics

Nothing is animated. Fixed 1/120 s timestep; magic-formula tires evaluated on the combined slip vector, so longitudinal and lateral grip share one friction circle — and the curve's tail past the peak is what makes a held drift a stable equilibrium instead of a knife edge. Tire relaxation length so the car takes a set instead of pivoting; a sprung 3-DOF chassis feeding per-wheel loads, so weight transfer genuinely changes the balance; 50° of angle-kit steering lock with caster self-centering, so the car countersteers with you rather than for you. The lead car is no spline puppet: it runs the same integrator with the same four inputs, driven by a tuned controller. Ram it, and physics decides what happens to both of you.

Medals are measured, not guessed

The physics core was extracted byte-identically into a headless harness and chased by an autopilot that presses only the player's four keys, at five skill tiers × 12 seeds. GOLD 44,000 · SILVER 26,000 · BRONZE 6,000 · QUALIFY 2,500. Gold sits just under a clean expert chase; the club-tier bot never lifted the multiplier off ×1 — that headroom is yours. Five badges, one hidden.

How this drop was made

Made in one automated session: the concept and this page were written first, a coding agent built the simulation and spent most of its effort on the tuning pass — sweeping yaw damping against a deliberately clumsy keyboard-driver model until a correction stopped meaning a spin — and the finished run was verified in a real headless browser (start card, live chase at ×2.95, crash-out results, zero console errors) before publishing. three.js is vendored in-repo; everything else is hand-rolled, and all audio is synthesized live in WebAudio.