Make a serious crash nearly the end of the car

The first calibration left an 85 km/h head-on at 65% chassis and
perfectly driveable, which made hitting a building at ninety an
inconvenience rather than a disaster. The reference crash now lands the
chassis at 23%, the tyres at 61% and the engine at 75% - ordered by
what a collision actually ruins.

That makes one crash survivable and two in a row the end of the car,
which is the shape the risk wants: a mistake you drive home from, and a
second mistake you do not.

The per-step cap moves up with it. It exists for the pathological case
- a car wedged between two colliders reporting forces in the billions -
and once it sits below a bad head-on it stops being a backstop and
becomes the number deciding every impact.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/sim/car.ts

@@ -125,9 +125,11 @@ const PERMANENT_SHARE = 0.3;
  * and 37% of its ceiling — in one hit, on a car whose whole economy pays about
  * 0.3 parts a mission. One crash ended the campaign.
  *
- * At 1.6e7 the same crash reads as 0.156 impact: about 15% of the chassis and a
- * permanent 4.7% off its ceiling. Expensive, survivable, and still the most
- * costly thing you can do to the car.
+ * At 1.6e7 the same crash reads as 0.154 impact. What that then costs is set by
+ * the coefficients below, and they are deliberately brutal: a proper head-on
+ * takes about four fifths of the chassis. Hitting a building at ninety should
+ * very nearly be the end of the car, and the first calibration here — which
+ * left it at 65% and driveable — made a serious crash into an inconvenience.
  */
 const IMPACT_REFERENCE = 1.6e7;
 
@@ -139,10 +141,12 @@ const IMPACT_REFERENCE = 1.6e7;
  * has no natural bound. Without a cap the tail of a bad landing is worth more
  * than the landing. This is what stops a single frame from writing off a part.
  *
- * Set well above the ordinary crash so it stays a backstop rather than the
- * number that actually decides what a collision costs.
+ * Set above even a bad head-on so it stays a backstop rather than the number
+ * that actually decides what a collision costs. It exists for the pathological
+ * case — a car wedged between two colliders reporting forces in the billions —
+ * not for the crash the player just had.
  */
-const MAX_DAMAGE_PER_STEP = 0.25;
+const MAX_DAMAGE_PER_STEP = 0.85;
 
 /**
  * Returns a new condition.
@@ -164,9 +168,11 @@ const MAX_DAMAGE_PER_STEP = 0.25;
 export function applyWear(c: CarCondition, w: WearInput): CarCondition {
   const impact = w.impactForce / IMPACT_REFERENCE;
   const damage: Subsystems = {
-    engine: w.throttle * w.dt * 1.5e-4 + impact * 0.32,
-    tires: w.distance * 2e-5 + impact * 0.5,
-    chassis: impact * 1.0,
+    // Ordered by what a collision actually ruins: the shell takes the worst of
+    // it, the tyres and suspension a good share, the engine least of all.
+    engine: w.throttle * w.dt * 1.5e-4 + impact * 1.6,
+    tires: w.distance * 2e-5 + impact * 2.5,
+    chassis: impact * 5.0,
   };
 
   const level = {} as Subsystems;

src/sim/sim.test.ts

@@ -46,43 +46,61 @@ describe('car condition', () => {
    */
   const HARD_CRASH = 2.47e6;
 
-  it('leaves a car driveable after one hard crash', () => {
+  it('very nearly ends the car in one head-on', () => {
     const c = applyWear(freshCondition(), {
       dt: 1 / 60,
       distance: 0.4,
       throttle: 0,
       impactForce: HARD_CRASH,
     });
-    // Expensive — the worst single thing that can happen to the car — but the
-    // campaign continues. The first pass wrote off the chassis in this one step.
-    expect(c.level.chassis).toBeGreaterThan(0.7);
-    expect(c.level.chassis).toBeLessThan(0.95);
-    expect(c.ceiling.chassis).toBeGreaterThan(0.9);
+    // Hitting a building at ninety is meant to be close to the end of it. The
+    // shell takes the worst, the tyres a good share, the engine least.
+    expect(c.level.chassis).toBeLessThan(0.3);
+    expect(c.level.chassis).toBeGreaterThan(0.1);
+    expect(c.level.tires).toBeLessThan(c.level.engine);
+    expect(c.level.engine).toBeLessThan(0.8);
+  });
+
+  it('is survivable exactly once, which is what makes it worth avoiding', () => {
+    // One is a disaster you drive home from. Two in a row is the end of the
+    // car, and that is the whole shape of the risk.
+    const one = applyWear(freshCondition(), {
+      dt: 1 / 60,
+      distance: 0.4,
+      throttle: 0,
+      impactForce: HARD_CRASH,
+    });
+    expect(one.level.chassis).toBeGreaterThan(0);
+    const two = applyWear(one, {
+      dt: 1 / 60,
+      distance: 0.4,
+      throttle: 0,
+      impactForce: HARD_CRASH,
+    });
+    expect(two.level.chassis).toBe(0);
   });
 
   it('caps what a single step can take, however violent the contact', () => {
-    // A pileup reports contact forces without any natural bound; without a cap
-    // one frame of a bad landing is worth more than the crash that caused it.
-    const c = applyWear(freshCondition(), {
+    // A car wedged between two colliders reports forces in the billions. The
+    // cap is for that, not for the crash the player just had — so it has to sit
+    // above even a bad head-on or it becomes the number deciding every impact.
+    const pathological = applyWear(freshCondition(), {
       dt: 1 / 60,
       distance: 0.4,
       throttle: 1,
       impactForce: 1e9,
     });
     for (const part of SUBSYSTEMS) {
-      expect(c.level[part]).toBeGreaterThanOrEqual(0.74);
+      expect(pathological.level[part]).toBeGreaterThanOrEqual(0.14);
     }
-  });
-
-  it('takes a sustained battering to write the car off', () => {
-    let c = freshCondition();
-    let crashes = 0;
-    while (c.level.chassis > 0 && crashes < 100) {
-      c = applyWear(c, { dt: 1 / 60, distance: 0.4, throttle: 0, impactForce: HARD_CRASH });
-      crashes++;
-    }
-    // Enough hard crashes to be a story about the driver, not one bad corner.
-    expect(crashes).toBeGreaterThan(5);
+    // And it must not be what decides an ordinary head-on.
+    const crash = applyWear(freshCondition(), {
+      dt: 1 / 60,
+      distance: 0.4,
+      throttle: 0,
+      impactForce: HARD_CRASH,
+    });
+    expect(crash.level.chassis).toBeGreaterThan(pathological.level.chassis);
   });
 
   it('lets a careful driver come out ahead of the parts they are paid', () => {