Tire Compounds | The Undercut Wiki

The Undercut ships with two compounds: Soft and Hard. (Medium exists in the code for backward compatibility but is never used by current strategies or the UI.) Compound choice is the single biggest tactical lever before each session.

The two compounds

Compound	Speed bonus	Wear multiplier	Heat behaviour
Soft	+1.5%	1.5×	Warms faster, narrower window
Hard	-1.0%	0.7×	Slower to warm, wider window

The speed bonus is zone-weighted:

Corners: 100% effect
Braking zones: 70% effect
Straights: 30% effect

So the Soft’s pace advantage is biggest in corners, smallest on straights — that’s why a Soft–Hard sequence on a corner-heavy track typically out-paces a Hard-only stint.

Wear curve

Tires have a wear distance (in metres) that ticks up every lap. The performance curve has four phases:

Green (0–10% wear) — slight under-grip, ramps up to peak as the tire scrubs in
Optimal (10–60% wear) — peak grip, this is where you want to spend most of the stint
Degradation (60–75% wear) — gradual lap-time loss, ~0.5–1.0% per 5%
Cliff (75–100%+ wear) — sharp drop, can be 5%+ pace loss per 5%

There’s a secondary cliff past 100% — running a stint catastrophically long stacks an extra penalty. Don’t try to extend a Hard stint past its 1.5× multiplier; the cliff doesn’t care.

The compound’s wear multiplier scales the cumulative distance, not the curve itself. So Soft hits the cliff faster:

Compound	Lifetime ratio	Approx laps before cliff (60s laps)
Soft (1.5×)	shorter	~14–18 laps
Hard (0.7×)	longer	~28–35 laps

(Track length affects exact numbers — tire_lifetime in RaceConfig is the base.)

Heat / temperature

Each compound has a different optimal temperature window. Outside the window, grip drops:

Compound performance in corners and braking is multiplied by tire temp_grip_factor — a temp-derived 0.0–1.0 modifier.
Soft warms faster (peak temp ~5–10s of running) but overheats easier (push-laps, dirty air, hot conditions).
Hard takes longer to come in (cold-tire penalty on out-laps is bigger), but stays in window once there.

The supplier’s heat_resistance rating widens this window — a tire-supplier heat_resistance: 8 makes Soft viable on a hot calendar where a heat_resistance: 3 would chunk.

When to pick Soft

Qualifying — almost always Soft. The pace difference is decisive over 1–2 hot laps.
Final stint of a 1-stop, when laps remaining are under Soft’s lifetime
Short circuits (Monaco-equivalent) where 1-stop is possible on Softs
Cold conditions where Hard never reaches optimal temp
Aggressive 2-stop strategy (start Soft, end Soft, swap Hard middle)

When to pick Hard

Long opening stint of a 1-stop strategy
Hot conditions where Soft would overheat
Long calendar (tracks that grind tires regardless of compound)
Conservative 1-stop where the goal is “finish with margin”
You started P-low and need long stints to gain via strategy variance

Compound + driver match

Driver consistency (CON) interacts with compound:

High CON (15+) + Soft = drivers manage the wear cliff well; viable longer Soft stints
Low CON (1–8) + Soft = wear curve hits faster (CON also reduces wear on top of compound multiplier); cliff arrives early
Low CON + Hard = the safer pairing; protects from wear-cliff DNFs

This is why a low-CON rookie is often parked on Hard for the long stint regardless of theoretical optimum.

Compound + car traits (planned)

When car traits land, compound interactions get spicier:

Hot Hatch car + Soft = +5°C wider thermal window; Soft viable on hot tracks
Late Cliff car + Hard = wear cliff at 90% instead of 75%; extreme long stints viable
Tire Whisperer car + Soft = 30% slower wear; Soft as the dominant compound choice

For now, treat compound choice as compound + supplier + driver.

Strategy interaction (briefly)

The 3 pre-generated strategies use compounds differently:

Strategy	Stint 1	Stint 2	Stint 3
A (Aggressive 2-stop)	Soft	Hard	Soft
B (Balanced 1-stop)	Soft	Hard	—
C (Conservative 1-stop)	Hard	Soft	—

See Pit Strategy Plans for when each one wins.

Out-lap penalty

Whatever compound you fit at a pit stop, you start 3% slower for ~2000m (pit_out_lap_decay_dist) — cold tires + cold brakes. INT-scaled (high-INT drivers handle out-laps better).

So a stop-loss isn’t just pit_service_time + pit_lane_speed; add ~3 seconds of out-lap pace deficit on top.

Quick reference

Scenario	Pick
Quali fast lap	Soft
Out-lap on cold day	Hard
50-lap race, average track	Strategy B (Soft → Hard)
50-lap race, tire-shredder	Strategy C (Hard first to extend stint 1)
30-lap sprint	Strategy A (2-stop Soft–Hard–Soft if pit-loss is short)
Low-CON driver	Bias toward Hard
`heat_resistance` supplier 9	Soft viable everywhere
`heat_resistance` supplier 3	Hard on hot calendars