The Lap Analysis Workflow tells you where time is being lost. The Data Channel Reference tells you what the traces mean. This page connects both to the car itself - which adjustments are permitted in your championship, what the factory specification ranges are, how to structure a test to get usable data, and what each change actually looks like in the channels when it works. The adjustment matrix is specific to your championship. Use the toggle to switch between classes.
The Test Day Methodology
A test day without structure produces noise, not data. The methodology here applies regardless of championship — the principles are universal. For the background on why sector-first analysis matters before touching setup, see the Lap Analysis Workflow. For channel interpretation during each run, see the Data Channel Reference.
Establish a baseline before the first change
The most common test day failure is arriving with a setup change already made. You have nothing to compare against. The first run of every test day must be in the configuration the car finished the previous event — or in a known, documented baseline. Minimum three clean laps, same driver, no traffic. This is your reference dataset. Everything that follows is measured against it.
If this is the car's first test, the baseline run is the factory setup at the correct alignment specification. Do not guess at settings — measure and record what is actually on the car before the session starts. Springs, damper settings, ARB positions, tyre pressures, tyre temperatures at the end of the run. All of it.
Change one thing at a time — without exception
This rule exists because it is the only way to attribute a lap time change to a specific adjustment. Change two things between runs and the data cannot tell you which one worked. Change one thing and the data can confirm or deny it within three laps.
The temptation at a test day is to make multiple changes between runs because track time is limited. Resist it. Two runs with one change each gives you two data points. One run with two changes gives you nothing usable. The apparent efficiency of changing multiple things at once is an illusion — you will spend the rest of the season uncertain which setting actually helped.
Control track state — or account for it
Track temperature and rubber build-up affect lap times by more than most setup changes. A circuit that has rubbered in through the morning will be 0.5-1.5 s faster in the afternoon with no changes to the car at all. If you are comparing a morning baseline against an afternoon setup change, the lap time improvement may be the track, not the setup.
The discipline: always check the fastest lap in each session against the circuit benchmark. If the whole field is 1.2 s faster in session 2 than session 1, your setup change did not produce the 1.0 s you are crediting it with. The channels tell the real story — lateral G at the affected corner, minimum corner speed. If the track improved, everyone's numbers go up. If your lateral G at the target corner specifically improved while the rest of the lap held constant, the setup change contributed.
For a cross-session comparison that is genuinely valid, use sector delta against another car in the same configuration — or against your own baseline from earlier in the same session, same track state.
Match tyre age across comparison runs
A tyre that has done 8 laps behaves differently from a new tyre. If your baseline run used new tyres and your comparison run used 12-lap tyres, the tyre condition is a confounding variable. For setup correlation work, the ideal is same tyre age at the start of each run — which typically means new or scrubbed tyres for the baseline and the same set, same lap count, for the comparison.
On the Pirelli Trofeo R control tyre used in Boxster Cup, the performance window is relatively narrow — the tyre comes in quickly on the outlap and degrades noticeably after 8-10 laps in dry conditions. Structure runs to stay inside that window. Three to five timed laps per run is the practical ceiling for meaningful setup data on this tyre.
Record the setup sheet after every run — not from memory later
Damper settings, spring rates, ARB position, tyre pressures hot and cold, tyre temperatures at all four corners immediately after the car comes in. All of it, every run, written down before the next change is made. Memory is unreliable and the value of the test day data depends entirely on being able to reconstruct exactly what was on the car for each run.
Tyre temperature distribution across the tread — inner, middle, outer — tells you camber and pressure story without a separate sensor. An inner edge consistently 15-20 degrees hotter than the outer is too much negative camber or too little pressure for the conditions. This reading is only useful if taken within 90 seconds of the car stopping.
Separate driver adaptation from setup improvement
A setup change that makes the car feel different will often produce faster lap times in the first run simply because the driver is paying more attention and driving more carefully. This is the placebo effect in motorsport and it is extremely common. The data exposes it: if the lap time improved but the lateral G, minimum corner speed, and sector delta at the target corner are unchanged, the driver adapted — the setup change may have done nothing.
The confirmation standard: lateral G at the affected corner must change in the predicted direction, minimum corner speed must reflect it, and the sector time must follow. All three moving together is a genuine setup improvement. Lap time alone is not sufficient evidence.
The Adjustment Matrix
Select your championship below. The matrix shows permitted adjustments, regulation references, Porsche factory specification ranges where applicable, and the data channel signature each change produces when it works. Factory alignment figures are from Porsche Workshop Manual specifications for standard road cars — competition setup within the permitted range will typically run toward the performance end of these tolerances.
986 Boxster S 3.2 (1999–2004)
What is permitted
Springs are free provided they are ferrous material. Non-ferrous springs (titanium, aluminium) are not permitted. The spring must fit within the standard OE mounting location — no extended perches or non-standard top mounts except as noted in 38.7.
In practice this means aftermarket steel coilover springs or standard-pattern progressive-rate springs are permitted. The spring rate range used in Boxster Cup typically runs 40-70 N/mm (228-400 lb/in) front and 50-80 N/mm (285-457 lb/in) rear depending on circuit and driver preference - roughly 1.5-2x the standard road rate, matched to the Trofeo R compound and single-adjustable dampers.
Factory reference
Porsche does not publish spring rates for road cars in workshop manuals — the figures below are well-established community measurements from standard cars.
| Model | Front | Rear |
|---|---|---|
| 986 S 3.2 (all) | ~28 N/mm (160 lb/in) | ~35 N/mm (200 lb/in) |
Porsche does not publish spring rates for road cars in workshop manuals — this figure is a well-established community measurement from standard 986 cars. Competition spring rates in Boxster Cup typically run 1.5-2.5x standard — broadly 40-70 N/mm front and 50-80 N/mm rear, matched to the Trofeo R compound and single-adjustable dampers. Stiffer front relative to rear increases understeer; stiffer rear increases oversteer tendency.
Data channel signature
Lateral G shape: Stiffer springs produce a sharper, faster Ay build at corner entry — the car loads the outside tyre more quickly. If the trace shows a faster rise to peak Ay after a spring rate increase, the change is working.
Minimum corner speed: A spring rate that is too stiff for the circuit will show as a lower minimum corner speed — the car becomes nervous on turn-in and the driver lifts. The speed trace will show earlier braking and a lower apex speed at the target corner.
Longitudinal G on exit: Rear spring rate affects traction zone stability. A rear that is too stiff shows as oscillation in Ax under acceleration — the car is skipping rather than driving through the exit.
What is permitted
Fixed or single-adjustable dampers only, on original unmodified chassis mounting points. Separate pressurised canisters or reservoirs are not permitted (38.5). Electronic dampers are not permitted (38.6). Solid non-adjustable spherical bearing top mounts are permitted (38.7).
Single adjustable means one dial controls both compression and rebound simultaneously (typically by adjusting a single needle valve). Truly separate compression and rebound adjustment on the same damper would constitute a dual-adjustable unit and is not permitted under 38.4.
Practical adjustment range
Most single-adjustable aftermarket dampers used in Boxster Cup (Bilstein B14/B16, KW Variant 1/2, Ohlins Road and Track) have 10-16 clicks of adjustment. The range that is useful for lap time work is typically the middle third — clicks 4-10 on a 16-click unit. The extremes are for road use (full soft) or highly specific circuit conditions (full stiff).
As a starting point for circuit use: 6-8 clicks from full soft on a 16-click unit. Adjust in steps of 2 clicks and run a minimum of 3 laps per setting before concluding anything.
Data channel signature
Lateral G at turn-in: Softer damping allows more body roll before the tyre loads — Ay builds more slowly at corner entry. Stiffer damping produces a sharper initial Ay spike at turn-in. If the trace shows a step change in the Ay build rate after a damper adjustment, the change is detectable.
Yaw rate at corner entry: Damper stiffness affects how quickly the car rotates. Too stiff front damping shows as a yaw rate lag at turn-in — the car is slow to respond. Too soft shows as an initial yaw spike followed by an abrupt plateau as the roll catches up with the steering input.
Longitudinal G under braking: Rear damper stiffness affects brake balance feel. A rear that is too stiff under braking shows as a sharp Ax spike followed by instability — the rear is locking the body movement and transferring load unevenly.
What is permitted
Roll bars including adjustable versions may be fitted provided they use all original manufacturer mounting points (38.9). Adjustable blade or slide adjustable ARBs are not permitted (38.10). Drop links are free including rose joints (38.11).
In practice this means a conventional multi-position adjustable ARB — one that changes stiffness by moving the drop link attachment point along the bar arm — is permitted. A blade ARB that changes stiffness by rotating the bar cross-section is not permitted. The standard Boxster ARB mounting points must be retained.
Factory reference — 986 Boxster S 3.2
| Spec | 986.1 S (1999-2002) | 986.2 S (2002-2004) |
|---|---|---|
| Front ARB dia. | 21 mm | 22 mm |
| Rear ARB dia. | 18 mm | 18 mm |
The 986.2 S carried a slightly stiffer front bar as standard compared to the 986.1 S. Worth noting when comparing baseline feel between cars of different years within the same grid.
Data channel signature
Lateral G mid-corner: A stiffer front ARB reduces body roll and loads the outside front tyre harder. This shows as a higher, flatter Ay peak through the mid-corner phase. If the trace shows a sustained Ay plateau higher than the baseline, the front ARB stiffening has increased front grip.
Understeer signature: Too much front ARB stiffness shows as a classic understeer pattern — Ay builds to a level and then plateaus without continuing to rise. The car has hit the front grip limit. Yaw rate will be lower than expected for the corner radius and speed.
Lateral G asymmetry: Compare left and right corners. Front ARB effects are symmetric — if only one direction shows the change, the issue is alignment or tyre pressure, not ARB.
What is permitted
Same rules as front ARB — adjustable versions permitted on original mountings, blade and slide types not permitted. The rear ARB is the primary balance adjustment in the Boxster. Moving to a stiffer rear ARB relative to front increases oversteer tendency; softer rear relative to front increases understeer.
The 986 Boxster carries more of its weight behind the front axle than a conventional front-engined car does. This rear-biased load distribution means the rear axle is the heavier end in cornering, making rear ARB adjustment more sensitive to balance than on a car where front-axle mass dominates the roll stiffness requirement.
Balance effect reference
The front-to-rear ARB ratio is more important than the absolute stiffness of either bar. As a starting reference for Boxster Cup on the Trofeo R:
Neutral balance: Front and rear ARB stiffness in proportion to axle loads. The 986 Boxster S carries approximately 44% of its weight over the front axle and 56% over the rear, so the rear axle is loaded harder in cornering. To achieve a balanced car, the rear ARB needs to be proportionally stiffer relative to the front to match its higher axle load — otherwise the rear will roll less than its load warrants and the car will tend toward understeer. This makes the rear ARB the primary balance tool in the Boxster.
Understeer (stability): Soften rear ARB relative to front. Suitable for circuits with high-speed corners where stability is valued over rotation.
Oversteer (rotation): Stiffen rear ARB relative to front. Useful for tight circuits where corner entry rotation is the limiting factor.
Data channel signature
Yaw rate at corner entry: A stiffer rear ARB increases yaw rate response at turn-in — the car rotates more readily. This shows as a faster yaw rate rise in the first 50-100 ms after the steering input. Compare the yaw rate onset slope before and after the change.
Oversteer signature: Too much rear ARB stiffness shows as a yaw rate spike mid-corner followed by a driver correction — the rear has stepped. This will appear on the Ay trace as a mid-corner spike coinciding with the correction input. The VBOX video overlay will confirm the rear movement.
Exit Ax stability: Oversteer on exit from a stiff rear ARB shows as Ax oscillation under acceleration — the driver is managing the rear rather than committing to throttle. Minimum corner speed will also suffer as a result.
What is permitted
Tyre pressure is free. Only atmospheric air is permitted as the filling medium (Reg 44.5) - nitrogen is not atmospheric air and is not permitted. Tyre heating devices, heat-retention blankets, and tyre treatments are prohibited (Reg 44.4), so pressures must be set cold and the operating pressure managed through the heat generated in use.
The Pirelli Trofeo R is sensitive to pressure. Running too low increases tyre temperature and wear and softens the sidewall — the car feels more responsive initially but degrades faster and ultimately has less lateral grip. Running too high reduces contact patch and reduces lateral G.
Operating pressure reference — Trofeo R
Pirelli publishes recommended operating pressures for the Trofeo R in circuit use. These are hot pressures — the pressure the tyre should be at after 2-3 laps of circuit driving.
| Front | Rear | |
|---|---|---|
| Cold set | 1.6-1.8 bar (23-26 psi) | 1.7-1.9 bar (25-28 psi) |
| Hot target | 2.0-2.3 bar (29-33 psi) | 2.1-2.4 bar (30-35 psi) |
Check hot pressures within 90 seconds of the car stopping. Adjust cold set to hit the hot target. The build varies with ambient temperature — on a cold day expect less build.
Data channel signature
Lateral G peak: Correct pressure shows as a clean, sustained Ay peak through mid-corner. Underinflation shows as a higher initial Ay spike followed by a drop — the sidewall flexes and the contact patch geometry changes mid-corner. Overinflation shows as a lower, flatter peak with less lateral G generated overall.
Tyre temperature distribution: If tyre temps are logged, correct pressure shows inner, middle and outer within 10-15 degrees of each other. High inner temperature relative to outer indicates either too much negative camber or too little pressure. High outer indicates too much pressure or insufficient camber.
Consistency across a run: Pressure that is set too low will show improving lap times for 3-4 laps as the tyre heats up, then degrading times as the tyre overheats. This pattern in the sector data is a pressure signature.
What is permitted
Only adjustment within the scope of the standard OE design is permitted (38.3). Wheelbase must remain standard with a maximum tolerance of +/-10 mm (38.16). This means camber and toe can be adjusted within the range the standard suspension geometry allows — no eccentric bolts, camber plates, or non-standard geometry components beyond those specifically permitted (GT3 lower arms or Eibach 572610K under 38.12).
The permitted lower arms (38.12) do allow a wider camber adjustment range than the standard arms — the GT3 street arm and Eibach 572610K both have additional adjustment in the inner bush position.
Factory alignment specs — 986 and 987
| Setting | 986.1 S (1999-2002) | 986.2 S (2002-2004) |
|---|---|---|
| Front camber | -0.25° to -1.25° | -0.25° to -1.25° |
| Rear camber | -0.75° to -1.75° | -0.75° to -1.75° |
| Front toe | 0° to +0.2° (in) | 0° to +0.2° (in) |
| Rear toe | +0.1° to +0.3° (in) | +0.1° to +0.3° (in) |
Factory alignment figures are from Porsche Workshop Manual specifications for the 986 road car. These are the OE tolerances within which Reg 38.3 requires adjustment to remain. Competition setup typically runs toward maximum negative camber front and rear, with minimal toe front and slight toe-in rear.
Data channel signature
Front camber — lateral G peak: More negative front camber increases front grip at the limit — peak Ay at medium-speed corners will increase. Too much negative camber reduces straight-line tyre contact and shows as increased sensitivity in the speed trace over bumps and kerbs.
Rear toe — yaw rate stability: More rear toe-in increases straight-line stability and reduces the tendency to oversteer on corner entry. This shows as a smoother yaw rate onset at turn-in — less initial spike. Too much rear toe-in reduces rotation and shows as a yaw rate that builds slower than expected for the corner radius.
Tyre temperature cross-check: Front camber is most efficiently validated by tyre temperature distribution. Target even temperatures inner to outer at the front — if the outer edge is consistently cold, more negative camber is needed. This is faster feedback than waiting for lap time data.
What is permitted
All models may use front and rear lower suspension arms from the GT3 street model, or Eibach sliding lower suspension control arms code 572610K. All variants must be fitted with rubber bushes — not spherical bearings. The tuning fork arm must attach through the centre position of the bush only.
The benefit of the permitted arms is primarily additional camber adjustment range compared to the standard arm, achieved through the sliding inner bush position. This allows more negative front camber than the standard arm permits within OE geometry scope.
Practical effect
The Eibach 572610K allows approximately 0.5-0.8 degrees of additional negative camber adjustment at the front compared to the standard lower arm. On the Trofeo R, this typically translates to better front tyre temperature distribution and improved mid-corner lateral G — particularly noticeable at medium to slow corners where front grip is the limiting factor.
The improvement is circuit-dependent. At high-speed circuits where understeer is not the primary issue, the effect is smaller. At technical circuits with multiple slow corners, the additional camber range can be worth 0.2-0.4 s per lap in the right conditions.
Data channel signature
Front lateral G: The primary confirmation channel. If the additional camber from the permitted arms is working, peak Ay at front-limited corners (typically slow to medium speed, long apex) will be higher than the baseline. The improvement should be consistent across multiple laps — a one-lap anomaly is not confirmation.
Tyre temperature inner edge: Before the permitted arms were fitted, if the inner front tyre edge was running significantly hotter than the centre, the standard arm was limiting camber adjustment. After fitting the Eibach arm and increasing camber, the temperature distribution should become more even.
What is permitted
Shock absorbers are unrestricted subject to fitting on the original unmodified mounting points and standard hub units (38.6). This is a significantly wider permission than Boxster Cup — multi-adjustable dampers with separate compression and rebound control, and remote reservoir units, are all permitted.
If canisters are fitted within the driver/passenger compartment they must be securely enclosed in metal panelling (38.7). Mechanical or electronic adjustment of the shock absorber while on track is not permitted (38.18).
Solid top suspension spherical bearing mountings are permitted on original mounting points (38.8).
Practical adjustment range
With unrestricted dampers the setup space expands considerably. Separate compression and rebound control allows the damper to be tuned independently for corner entry (compression) and corner exit (rebound) behaviour — something the Boxster Cup single-adjustable unit cannot do.
Compression (bump): Controls how quickly weight transfers under braking and at corner entry. Stiffer compression = faster weight transfer = sharper initial response but potentially less traction on uneven surfaces.
Rebound: Controls how quickly the suspension returns after compression. Too fast rebound on exit causes the tyre to lose contact with the road over bumps. Too slow traps the suspension compressed and reduces available travel for the next input.
Data channel signature
Compression effect — Ay onset: Stiffer compression shows as a faster Ay rise at corner entry. Softer compression shows a more gradual build. The optimal onset rate is the fastest that still allows smooth lateral G — a step change or spike at turn-in indicates too stiff.
Rebound effect — exit speed: Correct rebound shows as a clean Ax build from the throttle point with no oscillation. Rebound that is too fast (shock returns too quickly) shows as Ax oscillation under acceleration — the tyre is bouncing. Rebound that is too slow shows as a gradual Ax build that never reaches full acceleration — the suspension is bottomed.
Separate corner validation: With two-way adjustable dampers, test compression and rebound changes at different corners — slow corners expose rebound (longer time in compression), fast corners expose compression rate.
What is permitted
Springs are free provided they are ferrous material (38.9). The same rule as Boxster Cup. With unrestricted dampers, spring and damper tuning can be done together — the damper can be set to complement the spring rate rather than compensating for it, which is the constraint in Boxster Cup.
Factory reference — Cayman S / Boxster S
| Model | Front | Rear |
|---|---|---|
| 987 Cayman S | ~34 N/mm (194 lb/in) | ~42 N/mm (240 lb/in) |
| 987 Boxster S | ~30 N/mm (171 lb/in) | ~38 N/mm (217 lb/in) |
| 986 Boxster S | ~28 N/mm (160 lb/in) | ~35 N/mm (200 lb/in) |
The Cayman S has slightly stiffer standard springs than the Boxster S due to the coupe body structure and different weight distribution. Competition rates on slicks with unrestricted dampers typically run 100-180 N/mm (571-1028 lb/in) front and 120-200 N/mm (685-1142 lb/in) rear. The Cayman S coupe platform tolerates the higher end of this range; the Boxster S convertible typically runs softer due to greater chassis compliance. These are significantly stiffer than Boxster Cup rates - the DHG slick generates substantially more lateral load and the unrestricted damper can be tuned to complement a stiffer spring in a way the single-adjustable unit cannot.
Data channel signature
Same channel signatures as Boxster Cup — spring rate affects Ay build rate, minimum corner speed, and Ax stability on exit. On the DHG slick the grip level is higher, so the spring rate needs to be correspondingly stiffer to control the body movement generated by higher lateral forces. A spring rate that was correct on road tyres will typically feel too soft on slicks.
Slick-specific note: The higher grip of the DHG slick means suspension movement under lateral load is greater. A spring that was correct on the Trofeo R will show increased body roll in the Ay trace when switching to slicks — not because the spring has changed, but because the grip has increased.
What is permitted
Adjustable rear toe arms with spherical bearings/rose joints are permitted, using standard mounting points (38.15). This is not permitted in Boxster Cup. The adjustable rear toe arm allows more precise rear toe setting than the standard eccentric bolt adjustment — and rose joints eliminate the compliance in the standard rubber bush that causes rear toe to change under load.
Bump steer spacers are not permitted (38.16). The wheelbase must remain standard within 10 mm (38.19).
Effect on balance
Rear toe-in provides straight-line stability and increases the tendency toward understeer — the rear is passively steering away from rotation. More rear toe-in means more stability at high speed but less rotation at slow corners.
Rose-jointed rear toe arms eliminate load-dependent toe change — under high lateral load, a rubber-bushed rear arm will deflect and change toe passively. The rose joint eliminates this compliance, making the rear behave more consistently at the limit and making the data more repeatable between laps.
Data channel signature
Yaw rate consistency: The most useful test for rose-jointed rear arms is to compare yaw rate lap-to-lap variance at the same corner. If rear toe is changing under load with rubber bushes, yaw rate at the same corner will vary more lap-to-lap than expected. After fitting rose-jointed arms, lap-to-lap yaw rate consistency at high-lateral-G corners should improve.
Toe-in increase effect: More rear toe-in shows as a reduced yaw rate onset at corner entry — the car is more reluctant to rotate. Too much toe-in shows as a flat Ay plateau at slow corners — the rear stability is preventing the rotation needed to generate lateral G at the front.
What is permitted
Any Porsche production anti-roll bar in unmodified form, including adjustable versions, may be fitted provided it uses original mounting points (38.10). Adjustable blade or slide adjustable roll bars are not permitted (38.11). Drop links are free including rose joints (38.12).
The permission to use any Porsche production ARB is wider than Boxster Cup, which requires original mounting points but does not explicitly permit bars from other Porsche models. In practice this means bars from the 911, Cayman GT4, or other Porsche production models are eligible if they fit the standard mounting points.
Factory reference — Cayman S
| Spec | 987.1 Cayman S | 987.2 Cayman S |
|---|---|---|
| Front ARB dia. | 22 mm | 23 mm |
| Rear ARB dia. | 20 mm | 21 mm |
The Cayman S has a stiffer ARB setup than the Boxster S as standard, reflecting the coupe's lower centre of gravity and stiffer body structure. On slicks, front ARB typically runs stiffer than standard to control the additional lateral load generated.
Data channel signature
Same signatures as Boxster Cup — stiffer front ARB increases front grip and moves balance toward understeer, stiffer rear ARB increases rotation and moves balance toward oversteer. On the DHG slick the effects are amplified — the higher grip level means ARB balance changes produce larger lateral G shifts than on the Trofeo R.
Slick-specific sensitivity: On slicks, the ARB balance sensitivity is approximately 1.5-2x that of a road tyre setup. Small ARB position changes that were barely detectable on road tyres will show clearly in the Ay trace on slicks. Adjust in small increments and run the full minimum 3-lap validation before concluding.
What is permitted
Only adjustment within the scope of the standard OE design is permitted (38.5). Wheelbase must remain standard within 10 mm (38.19). Same overall constraint as Boxster Cup, but the additional permitted lower arms (38.13) and adjustable rear toe arms (38.15) provide more adjustment range than the standard car.
Uprated rubber bushes are permitted (38.3) — this is not permitted in Boxster Cup. Stiffer bushes reduce compliance-induced geometry change under load, effectively making the alignment more consistent at the limit.
Factory alignment specs — Cayman S
| Setting | 987.1 Cayman S | 987.2 Cayman S |
|---|---|---|
| Front camber | -0.3° to -1.3° | -0.3° to -1.3° |
| Rear camber | -1.0° to -2.0° | -1.25° to -2.25° |
| Front toe | 0° to +0.2° (in) | 0° to +0.2° (in) |
| Rear toe | +0.1° to +0.3° (in) | +0.1° to +0.3° (in) |
The 987.2 Cayman S has slightly more rear camber range than the 987.1 as standard. On DHG slicks, competition alignment runs toward maximum negative camber at all four corners.
Data channel signature
Same channel signatures as Boxster Cup alignment section. On slicks the tyre temperature feedback is faster and more pronounced — a camber error that might take 5 laps to show on a road tyre will be visible in tyre temps within 2 laps on a slick.
Uprated bush effect: If stiffer bushes have been fitted, compare yaw rate lap-to-lap variance at high-lateral-G corners before and after. Reduced variance indicates the geometry is more consistent under load — the bush compliance was causing alignment change that is now eliminated.
The principle
Spring rate controls how quickly load transfers between axles and between inside and outside tyres. A stiffer spring transfers load faster — the tyre reaches its operating state more quickly but with less suspension travel to absorb surface variation. A softer spring allows more body movement but gives the tyre more time and travel to maintain contact.
The correct spring rate depends on the tyre compound, the circuit surface, and the weight of the car. As a general rule, the minimum spring rate that controls body movement adequately for the grip level of the tyre is the right starting point — stiffer than this reduces lap time without providing any benefit.
Front-to-rear balance
Stiffer front relative to rear: More load transfer at the front, less at the rear. Front tyre reaches its limit first. Understeer tendency increases.
Stiffer rear relative to front: More load transfer at the rear, less at the front. Rear tyre reaches its limit first. Oversteer tendency increases.
The neutral balance point depends on the car's weight distribution. A front-heavy car needs a proportionally stiffer front spring to achieve neutral balance — and vice versa for a rear-heavy car.
Data channel signature
Ay build rate: A stiffer spring produces a faster lateral G build at corner entry. Compare the slope of the Ay trace from the steering input to the peak — this is the most direct measurement of spring rate effect in the data.
Minimum corner speed: Too stiff a spring for the circuit surface or grip level shows as reduced minimum corner speed. The car is harsh over kerbs and surface variation, and the driver reduces speed to compensate.
Consistency: A spring rate that is correctly matched to the circuit shows consistent Ay peaks lap-to-lap. High variance in peak Ay at the same corner is often a spring that is too soft — the body position varies, and so does the grip.
The principle
Dampers control the rate of suspension movement — they do not support the car (that is the spring's job) but they control how quickly the spring compresses and returns. The correct damper setting complements the spring rate: a stiffer spring needs less damping to control it; a softer spring needs more.
For a single-adjustable damper, the single dial typically controls a blended compression and rebound characteristic. Stiffer = faster load transfer and more resistance to both compression and rebound. For a two-way adjustable unit, compression and rebound can be tuned independently.
Corner entry vs exit separation
Corner entry (compression): The damper compresses as the car turns in and loads the outside tyre. Stiffer compression gives sharper initial response. Too stiff causes the tyre to lose contact with surface variations at turn-in.
Corner exit (rebound): The damper extends as the car unloads on exit. Too fast rebound causes the tyre to bounce off the road surface under acceleration. Too slow traps the suspension compressed and reduces available travel for the next corner.
Data channel signature
Ay onset — compression effect: Stiffer compression shows as a faster Ay build at corner entry with a more defined initial spike. Too stiff shows as a step change — an abrupt Ay onset rather than a smooth build. The ideal is a fast but smooth Ay rise to peak.
Ax exit — rebound effect: Too fast rebound shows as oscillation in the Ax trace under acceleration — the tyre is bouncing as the suspension returns rapidly. Too slow shows as a gradual Ax build without reaching full acceleration. Correct rebound shows as smooth, sustained Ax growth from the throttle point to full acceleration.
The principle
Anti-roll bars connect the left and right suspension on each axle. When one side compresses in a corner, the ARB resists the difference in compression between left and right — reducing body roll and increasing the load on the outside tyre relative to the inside tyre. A stiffer ARB at an axle increases the load transfer at that axle under cornering.
ARBs are the primary balance adjustment in most production-based race cars because they affect front-to-rear balance without changing spring rate — and they are usually adjustable at the circuit without removing wheels.
Balance effect
Stiffer front ARB: More load transfer at the front axle. Outside front tyre works harder. At the limit, the front reaches grip saturation first — understeer. In data: higher Ay peak but earlier plateau at fast corners.
Stiffer rear ARB: More load transfer at the rear axle. Outside rear tyre works harder. At the limit, the rear reaches saturation first — oversteer tendency. In data: faster yaw rate onset, potential for yaw rate spike on exit if rear breaks away.
Data channel signature
Understeer — front ARB too stiff: Ay builds to a level and stops. Yaw rate is lower than expected for the corner radius and speed. Driver is adding steering lock mid-corner but lateral G is not responding.
Oversteer — rear ARB too stiff: Yaw rate spike on corner exit coinciding with a mid-corner Ay disturbance. Driver correction visible as a brief reduction in Ay followed by a re-application. VBOX video will show the rear stepping.
Test discipline: Test ARB changes on the same corner every run. Choose a corner that is representative of the problem — slow corner for rotation, fast corner for stability. Use sector delta at that corner as the primary measure, not overall lap time.
The principle
Tyre pressure controls the contact patch geometry. Too low and the sidewall flexes excessively, the contact patch deforms, tyre temperature builds unevenly, and wear increases. Too high and the contact patch is reduced to the centre of the tread, lateral grip drops, and the tyre becomes sensitive to surface irregularity.
The correct pressure is the one that puts the tyre in its optimal operating temperature range with an even temperature distribution across the tread width. This varies with tyre compound, car weight, circuit, ambient temperature, and driving style.
Setting and validation
Always set pressure cold and measure hot. The pressure build from cold to operating temperature is typically 0.3-0.6 bar for a performance road tyre, 0.4-0.7 bar for a semi-slick, and 0.5-0.9 bar for a slick. Take hot pressures within 90 seconds of stopping.
Tyre temperature across the tread tells you more than pressure alone. Divide the tread into three zones: inner edge, centre, outer edge. All three within 15 degrees of each other is the target. Inner hotter than outer indicates too much negative camber or too little pressure. Outer hotter than inner indicates too little camber or too much pressure.
Data channel signature
Lateral G profile: Correct pressure shows a smooth, sustained Ay peak. Underinflation shows a higher initial spike that drops mid-corner as the sidewall deflects. Overinflation shows a lower, flatter peak with less total lateral G generated.
Lap-to-lap degradation: Pressure that is too low shows a performance pattern — improving for 3-4 laps as the tyre heats, then degrading as it overheats. In the sector data this appears as a best lap in lap 3 or 4 followed by progressively slower sector times. Correct pressure shows sustained performance across 5-8 laps before any degradation.
Reading the Setup Requirement from the Data
The adjustment matrix tells you what a change looks like in the data after you have made it. This section works the other way — how to read the channels at the end of a session and identify what the car needs before any adjustments are made. Getting this right means the first change at a test day is an informed hypothesis, not a guess.
Step 1 — Rule out technique before touching setup
Before any setup diagnosis, establish whether the driver is at the grip limit of the car. Look at peak lateral G at medium-speed corners and compare against the expected ceiling for the tyre and conditions. On a Pirelli Trofeo R in dry conditions a well-driven Boxster Cup car should reach 1.4-1.7 g at medium corners. On a DHG slick in Champ AM, expect 1.8-2.2 g. A driver consistently 20-30% below these figures is not at the limit — setup changes will not help and may actively confuse the driver's reference feel.
The threshold for setup work: the driver must be within 10-15% of the grip ceiling consistently across multiple laps before setup changes are worth making. Below this threshold, the coaching work from Part 1 produces more lap time than any setup change.
Step 2 — Identify whether the problem is entry, mid-corner, or exit
The speed trace tells you where in the corner the time is being lost. The setup diagnosis follows directly from this — the phase of the corner that shows the deficit points to the axle and the type of adjustment needed.
Entry problem (braking zone to apex): Minimum corner speed is lower than reference. The driver is either arriving too slow (previous corner exit issue — not a setup problem here) or the car is not rotating cleanly to the apex. Lateral G rises slowly at turn-in. Likely front setup — spring too stiff preventing front tyre from loading, or insufficient front camber, or front ARB too soft giving poor response.
Mid-corner problem (sustained lateral G): Apex speed is low but braking was clean. Lateral G plateaus before the geometric apex — the car has hit a grip ceiling mid-corner. Could be front (understeer plateau — yaw rate low, steering lock increasing) or rear (oversteer — yaw rate spike, driver correction visible). ARB balance is the first adjustment to investigate.
Exit problem (throttle application to straight): Minimum corner speed is fine but the car does not accelerate cleanly from the apex. Ax oscillation under acceleration, or the driver is late to throttle consistently. Rear stability issue — rear spring or damper, or rear ARB too stiff causing snap oversteer on exit.
Step 3 — Check balance symmetry left and right
Compare lateral G peaks at equivalent left and right corners of similar speed and radius. In a correctly balanced car, the Ay magnitude should be symmetric — a 1.5 g left corner should produce a similar 1.5 g right corner of the same type. Asymmetry points to a setup issue that is not balance-related — tyre pressure difference left-to-right, an alignment error on one side, or a damper that is behaving differently on one corner of the car.
This check takes less than two minutes in AiM Race Studio with the channel overlay view. It eliminates a significant category of false positives before any setup changes are made.
Step 4 — Form one hypothesis per session
Every setup diagnosis session should end with a single, specific hypothesis. Not "the car needs more front grip" — that is an observation. A hypothesis is: "the front ARB is too soft causing slow Ay build at turn-in at corners 3 and 7 — stiffen front ARB by one position and validate at those two corners specifically." This is testable, falsifiable, and scoped. If the data after the change shows faster Ay onset at corners 3 and 7 and improved minimum corner speed, the hypothesis was correct. If not, the data from the test run gives you the next hypothesis.
Setup and Test Day Questions
The questions that come up at the garage door before a test day starts.
Lap time alone cannot answer this question when track conditions have changed. The channels can. Look at lateral G at the specific corner where the setup change was targeted. If the setup change worked, peak Ay at that corner should have increased — independently of what the rest of the circuit did. If the whole lap is faster but Ay at the target corner is unchanged, the track improved, not the car.
The most reliable validation method when conditions are variable: use a car running in the same configuration as your baseline as a reference throughout the day. If both cars improve at the same rate but your target corner improves more, you have isolated a genuine setup effect. This is standard practice at multi-car team events like SupaTune Motorsport's Porsche Club GB programme — one car as a floating reference, others testing changes.
Check the channels at the target corner first. If Ay increased, minimum corner speed increased, but the lap time did not follow, the setup change worked locally but the driver has not yet carried the improvement through to the following corner — the sector delta gain was neutralised by a loss elsewhere. This is common in the first run after a change: the driver is managing a different car feel and has not yet driven to the new capability.
If the channels at the target corner also show no change — the setup adjustment made no measurable difference to lateral G or minimum speed — then "feels better" is likely the placebo effect. The driver is paying more attention after a change and driving more carefully. The data is the ground truth. If the channels did not move, the change did not help.
The rule: never make a second setup change in response to a subjective feeling that is not confirmed by channel data. Wait for the data to confirm or deny the first change before moving on.
Yes — with important caveats. The useful comparison is channel shape, not absolute values. Two drivers in the same car at the same circuit will show different Ay peaks, different braking points, different minimum corner speeds — because they drive differently. What is comparable is the shape of the Ay trace at specific corners, the yaw rate onset at turn-in, and the Ax profile under braking.
If driver A shows a smooth Ay arc through a corner and driver B shows a plateau with no peak — same car, same setup — the car is not understeering for driver A but is understeering for driver B. This tells you the setup is not the limiting factor for driver A (who is driving around the limit of the front) but might be for driver B (who has hit the front grip ceiling before the apex).
The most valuable multi-driver comparison in a regulated class like Porsche Club GB is comparing the fastest car in the field against a car that is consistently slower by the same amount in the same sector. If the channel shapes match but the absolute values differ, the problem is technique. If the channel shapes differ — one shows understeer plateau and the other does not — the setup or tyre condition is different.
Three, at most four, if conditions are stable and the changes are straightforward. The arithmetic is simple: a minimum of 3 clean laps per run, plus an install lap, plus a cool-down lap is 5 laps minimum per run. A typical test day session is 20-30 laps. That gives you 4-6 usable runs — one baseline, three to four changes, one confirmation run.
In practice, the constraint is usually tyre life rather than session length. On the Pirelli Trofeo R, the useful performance window on a single set is approximately 8-12 laps in dry conditions. If you run the baseline on new tyres, you have one change on those tyres before the performance falls away. After that, any comparison involves a tyre condition variable.
The most effective test day structure: baseline on new tyres (3-5 laps), one primary change (3-5 laps on same tyres), confirmation or second change on a second set (3-5 laps), and a final confirmation lap at the end of the day to lock in the conclusion. Four distinct data sets, one tyre swap, one conclusion.
This is a balance compromise and it is the normal outcome of most setup changes. No single adjustment improves every corner equally — stiffening the front ARB helps slow corners where front rotation is needed but hurts fast corners where the front was already at the limit. The decision is whether the net sector delta across the lap is positive.
Calculate the sector delta at both affected corners before and after the change. If corner 3 gains 0.15 s and corner 7 loses 0.08 s, the change is worth keeping — the net gain is 0.07 s and the circuit has more corners like 3 than like 7. If the loss at corner 7 equals or exceeds the gain at corner 3, the change is not worth keeping for this circuit — but it may be correct for a circuit with more corners of the type that improved.
This is why setup notes are circuit-specific. A front ARB position that is correct at Silverstone National may not be correct at Brands Hatch Indy. The data from each test day belongs in a circuit-specific setup file, not a single universal setup sheet.