Order of priority for changes
When you feel understeer or oversteer, don't change everything at once: change one parameter at a time, in this order, and test before moving to the next.
| # | Parameter | Why this position | If you have UNDERSTEER | If you have OVERSTEER |
|---|
| 1 | Anti-roll bars (ARB) | Big, immediate, and very predictable effect on balance; it doesn't change total mechanical grip, only how it's split between the two axles. It's the first knob to turn. | Soften front and/or stiffen rear. | Stiffen front and/or soften rear. |
| 2 | Differential (preload/power/coast lock) | Second in importance: acts specifically on entry (coast) and exit (power), the phases where you usually feel the problem most clearly. | Reduce power lock (exit) or coast lock (entry/trail-braking) | Increase power lock (exit) or coast lock (entry/trail-braking) |
| 3 | Camber | More "global" effect: changes the grip available on an axle in corners, but also affects straight-line braking and tire wear/temperature — needs to be dosed more carefully. | More negative front (or less negative rear) | More negative rear (or less negative front) |
| 4 | Toe (in/out) | Fine adjustment: real but smaller effect, useful for fine-tuning after sorting ARB/differential/camber, not as a first fix. | Less toe-in front, less toe-in rear | More toe-in rear, more toe-out front |
| 5 | Wings/Aero (splitter and wing) | Last because the effect depends on speed (only matters in fast corners) and costs drag/top speed — used more to adapt to the track than to fix a general flaw. | More front load / less rear | More rear load / less front |
General rule: anything that reduces front grip (relative to the rear) leads to understeer; anything that reduces rear grip (relative to the front) leads to oversteer.
Front/rear detail per parameter
| Parameter | FRONT adjustment | Effect | REAR adjustment | Effect |
|---|
| Toe (in/out) | More toe-in | More stability, less agility on entry → understeer in corners, but more stable under braking | More toe-in | More stability mid-corner/on exit → reduces oversteer (standard setup for stability) |
| More toe-out | Faster/more agile entry, less initial understeer, but less stable under braking (nervous) | More toe-out | More reactive rear end but less stable → more oversteer, especially under trail-braking |
| Camber | More negative | More front lateral grip in corners → reduces understeer, but less grip under straight-line braking | More negative | More rear lateral grip → reduces oversteer, but less traction on exit |
| Less negative | Less front lateral grip → more understeer, but more braking grip | Less negative | Less rear lateral grip → more oversteer, but more traction on exit |
| Anti-roll bar (ARB) | Stiffer | More front load transfer → less front grip → more understeer | Stiffer | More rear load transfer → less rear grip → more oversteer |
| Softer | Less front load transfer → more front grip → reduces understeer (relatively more oversteer) | Softer | Less rear load transfer → more rear grip → reduces oversteer (relatively more understeer) |
| Differential | (not applicable, rear-wheel drive) | — | Higher preload/power lock (on-throttle) | More stability on exit, less inside-wheel spin, but can cause understeer under traction if too high |
| Lower power lock | Freer rear end under acceleration → risk of oversteer under traction (especially with high power) |
| Higher coast lock (off-throttle/release) | More stable rear end on release/trail-braking → less rotation, tends to understeer on entry |
| Lower coast lock | Freer rear end on release → more rotation on entry, but risk of oversteer under trail-braking |
| Wings/Aero (splitter/wing) | More load (higher angle) | More front grip at high speed → reduces understeer in fast corners | More load (higher angle) | More rear grip at high speed → reduces oversteer in fast corners, more braking stability, but more drag |
| Less load | Less front grip at high speed → more understeer in fast corners | Less load | Less rear grip at high speed → more oversteer/instability in fast corners and under heavy braking |
Aero effects (wings/splitter) depend on speed — they matter a lot in fast corners (Pouhon, Blanchimont, Eau Rouge) and almost nothing in slow corners (La Source, Bus Stop), where mechanical grip dominates instead (bars, camber, toe, differential).
Clutch-plate differential: preload and number of plates
With a clutch-plate differential you have two separate levers, not just one, and they act differently.
| Setting | What it does | If you increase it | If you decrease it |
|---|
| Preload | Sets the baseline minimum lock, present even at low load (e.g. just off the throttle or with a trickle of gas) | Rear end more stable and "closed" right from the start → more understeer under traction and light release | Rear end freer right from the start → more rotation, more potential oversteer, but also less clean traction on exit |
| Number of plates | Sets the maximum locking torque the differential can generate as load rises (lots of power, hard braking) — it's the "gain" of the lock, not the baseline level | Much sharper, more sudden lock at high-load moments → strong understeer exiting slow corners or under heavy trail-braking, more "on/off" response | Even at the same preload the differential stays freer under high load → more oversteer under traction on slow corners/uphill exits, softer and more progressive response |
In practice: preload decides how the car behaves "at rest" (release, fast corners at constant throttle), the number of plates decides how it behaves in the most extreme moments (full throttle exiting a tight corner, hard braking on entry). If you only get understeer on slower/uphill exits, check the number of plates before the preload: you're probably locking too much exactly when you need less.
Typical front vs rear ratio
Common starting ratios used in GT3s (then refine track by track). Alongside, a real-world example: a published BMW M4 GT3 setup at Spa.
| Parameter | Typical Front vs Rear ratio | Real example (Spa, M4 GT3) | Why |
|---|
| Camber | Front ~0.3-0.5° more negative than rear | Front -4.0° / Rear -3.5° | The front works harder under combined braking+steering (trail braking), the rear needs more tire on the ground for traction |
| Toe | Front slightly toe-out, rear neutral or slightly toe-in | Front -0.2° / Rear 0° | This makes the front more responsive on entry, while the rear stays stable under traction/braking |
| Anti-roll bar (ARB) | Often similar, with the front slightly stiffer on tracks that need more rotation, or reversed if you need more traction on exit | Front 2 / Rear 2 (equal, on a 0-10 scale) | There's no fixed ratio: it's the fine balance lever, it depends on the character you want to give the car |
| Wings/Aero | Rear tends to carry proportionally more load than the front (balance shifted toward the rear for stability) | Front splitter 0mm / Rear wing 8 of 10 | GT3 cars are designed to be slightly understeery/stable at high speed: too much front load without matching rear load is dangerous in fast corners |
| Differential | Not applicable — rear only (rear-wheel drive) | Preload 170 Nm | — |
In short: camber and toe follow a fairly consistent ratio (more aggressive up front, more stable at the rear), while ARB and wings are more "by feel" and depend on the track — at Spa for example the wing stays high because there are many fast corners, while on a slower track the ratio would change.
Springs, dampers and bump stops (bottoming-out and compression/crest corners)
These parameters don't directly affect understeer/oversteer "in a clean corner" like toe/camber/ARB do, but rather how the car handles compressions and crests (Eau Rouge-Raidillon, kerbs, bumps) — and a problem there often feels like sudden under/oversteer precisely because the tire momentarily loses contact.
| Parameter | What it does | If stiffer | If softer |
|---|
| Springs (rate) | Determines how much the suspension compresses under load (aero, cornering, over bumps) | Less squat/less bottoming-out, but less mechanical grip over kerbs and bumps, more nervous car | More mechanical grip and better bump absorption, but higher risk of bottoming out under heavy compressions (e.g. Eau Rouge) and more pitch |
| Dampers — compression (bump), slow/fast | Controls the speed at which the suspension compresses, not how much it compresses | Sharper response to slow load transfers (braking/acceleration) or better absorbs fast hits (fast bump) if stiffened the right way; too stiff on fast bump = harsh hits transmitted to the chassis over bumps | More filtering of hits, but less control of load transfers, "softer/slower" feeling |
| Dampers — rebound, slow/fast | Controls the speed at which the suspension extends back after a compression (e.g. right after a crest or kerb) | The tire stays in contact longer after a bump/crest → more predictable but can feel "slow" in quick direction changes | The suspension extends back faster → risk the tire "jumps"/unloads over a crest, causing wheelspin under traction or a moment of light steering |
| Bump stop (rate and range) | Secondary end-of-travel spring that kicks in when the suspension runs out of normal travel — prevents metal bottoming-out and gives progressive final support | Firmer, earlier support in the travel → less bottoming-out but a harsher transition if the range is too short | Smoother, more progressive transition, but if too soft/long the bottoming-out still happens, just later |
Practical application — Eau Rouge-Raidillon
In your telemetry (lap 2:19.325) the front and rear-left ride height hits 0.0mm right on the crest of Raidillon, with a +1.58G vertical spike under compression followed by an unload down to -1.02G at the crest — this lines up exactly with where you lift off the throttle. In a case like this the most effective lever isn't ARB/camber/toe but: a slightly more progressive bump stop (longer range, softer initial rate) to better absorb the impact, possibly a few extra mm of rear ride height, and a rear rebound that isn't too fast so the tire doesn't unload too quickly right after the crest, exactly when you want to get back on the throttle.
Diagnosing via tire temperatures (camber and pressure)
With a 3-point pyrometer (inner, middle, outer), measured with the tire properly up to temperature (after 5-10 real laps, right after the last lap), you can diagnose camber and pressure from the same three numbers.
| What you're comparing | Reading | Diagnosis |
|---|
| Camber: inner shoulder vs outer shoulder | Inner much hotter than outer | Too much negative camber — the outer edge isn't touching enough asphalt |
| Outer much hotter than inner | Not enough negative camber (or too much toe-in) |
| Small difference (~5-10°C, good target ~7°C) | Camber is correct |
| Pressure: middle vs average of (inner+outer)/2 | Middle hotter than both shoulders | Tire overinflated — the tread works harder in the middle, less contact patch |
| Middle colder than both shoulders | Tire underinflated — the edges carry more load and run hotter |
| Middle ≈ average of the two shoulders | Pressure is correct, flat and even contact patch |
These are two independent diagnoses on the same three numbers — first look at inner/outer for camber, then the middle relative to the average of the two for pressure.
Quick cheat sheet
Got understeer? Try one or more of these:
- Softer front anti-roll bar (or stiffer rear)
- More negative front camber
- Less front toe-in
- More front aero load
- Less power lock on the differential (if understeer on exit)
Got oversteer? Try the opposite:
- Softer rear anti-roll bar (or stiffer front)
- More negative rear camber
- More rear toe-in
- More rear aero load
- More power lock on the differential (if oversteer under traction) or more coast lock (if oversteer on release/trail-braking)
