RC Tuning Expert — Setup Building Method

🔑 The Golden Rule

Always work from coarse to fine.

Get the big things right first: ride height, camber/toe, spring rates, damper settings.
Then medium things: shock position, roll center, anti-dive.
Then fine things: bump steer, shim stacks, reactive caster.

If you start with shims before your springs are right, you'll just be chasing your tail.

📋 Before You Start

Input	Why It Matters
Chassis	Geometry is chassis-specific. Shock pickup points, roll centers, pillow ball spacing — all differ by model.
Surface	High-grip carpet vs low-grip asphalt dictates spring rates, ride height, damper settings.
Track type	Technical (tight) vs speed (open) changes priorities: rotation vs stability, gearing, roll distribution.
Driving style	Smooth drivers can run stiffer; aggressive drivers need more mechanical grip and forgiveness.

⚡ Quick Start: The Builder generates a complete setup from these 4 inputs.
POST /api/v1/setup-builder/build
→ Open Setup Builder

🔄 Coarse → Fine Flow

1. Chassis → 2. Ride Height → 3. Camber/Toe → 4. Springs/Dampers → 5. Shock Geometry → 6. Roll Center → 7. Anti-Dive/Squat → 8. Bump Steer → 9. Fine Shims → 10. ARS → 11. Electronics → 12. Validate

1 Chassis & Baseline Geometry

Load the correct geometry database for your chassis. Every chassis has unique shock pickup points, roll center locations, A-arm geometry, pillow ball locations, and steering geometry.

Shock mount type: Tower-mounted (Associated, Yokomo, etc.) vs. Shim-mounted (XRAY T423-T426). This changes how you adjust shock angle (Step 5).
ARS equipped? If yes, the rear toe curve must be set up before fine-tuning rear geometry (Step 10).

GET /api/v1/setup-builder/chassis/{id} — Full geometry, spring catalog, ARB catalog, shock mount type
GET /api/v1/chassis-compare — Side-by-side chassis comparison
→ Pick your chassis in the Builder

2 Ride Height

The single most fundamental setup parameter. Affects CG height, roll center baseline, anti-dive/squat, and weight transfer.

Surface	Front (mm)	Rear (mm)
High-grip carpet	5.5–7.0	6.0–7.5
Standard carpet	6.0–7.5	6.5–8.0
Asphalt (smooth)	6.5–8.0	7.0–8.5
Asphalt (rough)	7.5–9.0	8.0–9.5

⚠ Critical: Set ride height BEFORE roll center, anti-dive, or shock geometry (Steps 5-8). Changing it later invalidates all downstream calculations.

Key relationships:

Lower ride height = lower CG = more overall grip, but bottoms out more easily
Rear higher than front (positive rake) = more high-speed stability
Front lower than rear = better turn-in, potentially less high-speed stability

3 Camber & Toe

Set tire contact patch orientation for maximum grip.

Camber

	Front	Rear
High grip	-2.5° to -3.0°	-2.0° to -2.5°
Medium grip	-2.0° to -2.5°	-1.5° to -2.0°
Low grip	-1.5° to -2.0°	-1.0° to -1.5°

More camber = more corner grip but less straight-line grip.

Toe

Front	Rear
0.5°–1.0° toe-out (turn-in)	2.0°–3.0° toe-in (stability)

Caster: 15°–25° total

More caster = more self-centering, more camber gain in turns. On XRAY T423-T426, caster is adjustable via front upper A-arm pillow ball shims.

GET /api/v1/calc/steering/ackermann — Ackermann percentage
GET /api/v1/calc/steering/bump-steer — Bump steer curve (do after camber/toe)

4 Springs & Dampers

Set roll stiffness distribution and ride frequency.

Spring Rates (kg/mm)

Surface	Front	Rear
High-grip carpet	2.7–3.5	2.5–3.2
Standard carpet	2.3–3.0	2.1–2.8
Asphalt	2.5–3.2	2.3–3.0
Low grip	1.8–2.5	1.6–2.2

Target 50–55% front roll stiffness for neutral handling.

Spring Color Code Mapping

Color	Associated	XRAY	Generic
Soft	—	Blue (2.5)	2.5 kg/mm
Medium	Gold (2.5)	Red (2.7)	2.7 kg/mm
Hard	Blue (2.7)	Gold (2.9)	3.0 kg/mm
X-Hard	Red (2.9)	—	—

Anti-Roll Bars (ARBs)

Fine-tune roll distribution without changing ride springs.

Stiffer front ARB → more understeer
Stiffer rear ARB → more oversteer
Start with: Medium front, medium rear. Fine-tune after test driving.

Damper Oil (cSt)

Surface	Front (cSt)	Rear (cSt)
High grip	15–25	12–20
Medium grip	10–18	8–15
Low grip	8–14	6–12

WT → cSt: 20WT≈10cSt, 30WT≈20cSt, 40WT≈38cSt, 50WT≈55cSt, 60WT≈75cSt, 70WT≈100cSt

Shock rebound target: 1.5–3.0mm at ride height (front and rear).

GET /api/v1/calc/weight-transfer/roll-stiffness — Roll distribution from springs + ARBs + track width

5 Shock Position & Geometry

Set shock angle for correct motion ratio and effective spring rate.

Tower-Mounted Chassis (Associated, Yokomo, etc.)

Use shock tower upper/lower mounting positions. Typical motion ratio: 0.70–0.85.

Shim-Mounted Chassis (XRAY T423-T426)

No conventional shock tower — angle set by shims at top mount:

Shim range: 0–4.5mm typical
Angle change: ~2.8° per mm
Typical: 2.0mm front, 1.5–2.0mm rear

Mugen

Uses built-in pickup point adjustment (designed into chassis). Functionally equivalent to shims.

Effective Spring Rate

Wheel rate = spring rate × (motion_ratio)²

Example: 3.0 kg/mm × (0.75)² = 1.69 kg/mm effective at wheel

⚠ On XRAY T423-T426: Tower shims raise the shock tower AND the upper A-arm bulkhead pickup points together (they're on the same structure). It's the upper arm pickup moving — not the shock angle — that changes roll center. Compensate with upper inner pickup adjustment. See Step 6.

GET /api/v1/setup-builder/shock-geometry — Angle, motion ratio, effective spring rate
GET /api/v1/calc/shock/motion-ratio — Full MR curve through suspension travel

6 Roll Center

Control weight transfer and chassis roll through roll center height.

	Front RC (mm)	Rear RC (mm)
High grip carpet	3.0–5.0	4.0–6.0
Asphalt (smooth)	2.0–4.0	3.0–5.0
Low grip	1.5–3.0	2.0–4.0

Handling effects:

Front RC high + Rear RC low → understeer
Front RC low + Rear RC high → oversteer
Higher RC = less body roll, more jacking
Lower RC = more mechanical grip, more body roll

XRAY T423-T426 (Shim-Mounted)

Upper mount shims on T4 raise the bulkhead — which moves both the shock tower position AND the upper A-arm pickup point. It's the A-arm pivot moving that changes roll center, not the shock angle. Use the upper inner pickup offset (~6mm range) to dial roll center independently.

GET /api/v1/setup-builder/roll-center — Height, roll axis angle
GET /api/v1/setup-builder/total-roll-center — All shim sources combined

7 Anti-Dive & Anti-Squat

Anti-Dive (Front — resists compression under braking)

0%: Neutral — arms horizontal, no geometric braking resistance (typical kit setup)
2–5%: Recommended starting point for touring cars
10%+: Very firm entry, front can feel "spiky" under braking

Anti-Squat (Rear — resists compression under acceleration)

0%: Neutral — arms horizontal, maximum rear squat (typical kit setup)
2–5%: Recommended starting point for touring cars
10%+: Rear can feel "twitchy" or kick under power

Typical target: 2–5% anti-dive, 2–5% anti-squat.

XRAY T423-T426: Adjust via front/rear lower inner pickup shims.

GET /api/v1/setup-builder/dive-squat — Anti-dive %, anti-squat %, geometry breakdown

8 Bump Steer

Unwanted toe change as suspension moves. Makes car unpredictable over bumps.

Target: Zero bump steer through normal travel (±5mm from ride height).

XRAY T423-T426 Tie Rod Shims

Shim Effect

Front tie rod inner Ackermann

Front tie rod outer Bump steer (keep minimal: 0.0–0.5mm)

Rear toe link inner Static rear toe

Rear toe link outer Rear bump steer

Steering Rack Shims

Front rack shim → affects Ackermann

Rear rack shim → changes steering pickup reference

Both equal → moves rack without geometry change

GET /api/v1/calc/steering/bump-steer — Bump steer curve from geometry + shims

9 Shim Stack Fine Tuning

You should be test-driving by now. Steps 1-8 give you a solid, fast setup. Step 9 is the last 5–10% optimization.

Shim Thickness Reference

Thickness Use Case

0.25mm Fine-tuning, minimum increment

0.50mm Standard adjustment step

1.00mm Standard adjustment, most common

2.00mm Maximum single shim (typical)

2.00–5.00mm Stacked shims for large changes

0–4.5mm XRAY T423-T426 top shock mount range

Reactive Caster (Pillow Ball Differential Shimming)

XRAY T423-T426: Upper A-arm has separate front and rear pillow balls.

Front Shim Rear Shim Effect

Equal (F=R) Pure caster change, no reactive

Front > Rear More caster + reactive caster (gains caster under braking)

Rear > Front Less caster + reverse reactive

GET /api/v1/setup-builder/reactive-caster — Front/rear reactive caster values
GET /api/v1/setup-builder/total-roll-center — All shim sources in one view

10 Active Rear Suspension (ARS)

ARS lets you control how rear toe changes through suspension travel. Set it for your track and driving style:

Toe-in on compression — rear stabilizes under power, cleaner exit on high-grip

Toe-out on compression — rear loosens on power, helps rotation on tight tracks

Toe-in on extension — rear stability under braking, good for fast entries

Adjust via ARS link length and pickup position. Neutral (zero toe change) is the default kit behavior.

GET /api/v1/ars — ARS-equipped chassis, toe curve data, link recommendations
GET /api/v1/calc/ars/toe-curve — Full toe-vs-travel curve

11 Electronics

Motor Timing (Mechanical / Endbell)

Class Typical Timing Range

Blinky — Stock 17.5T / 13.5T 40–45° 30–45° mechanical

Blinky — 10.5T 35–40° 25–40° mechanical

Modified 45–55° 35–55° mechanical (max ~55°)

Blinky class rules: No ESC timing advance. Only mechanical (endbell/hardware) timing. Most competitive blinky setups run 40–45° mechanical. Less timing = less top speed, more punch. More timing = higher RPM but more heat and can feel "flat."

Modified: Max practical mechanical timing is around 55°. Past that you get diminishing returns — heat goes up, efficiency drops, and the power band gets peaky.

ESC Settings

Parameter Low Grip Default High Grip

ESC timing (Modified only) 0° (stock) 5–10° 10–20°

Punch 7–10 4–6 1–3

Drag brake 5–10% 15–25% 15–25%

Brake force 80–100% 50–75% 25–40%

⚠ Motor temp limit: Keep below 80°C / 176°F. Timing increases heat — monitor after each run.

GET /api/v1/esc — ESC presets and manufacturer recommendations

12 Lap Time Prediction & Validation

Validate your full setup against the physics engine.

GET /api/v1/lap-time/predict — Predicted lap time + sector breakdown
GET /api/v1/lap-time/sensitivity — Which parameters matter most at this track
GET /api/v1/setup-diff — Compare old vs new setup with handling impact prediction
GET /api/v1/setup-sheet/generate — Generate printable PDF setup sheet
GET /api/v1/setup-sheet/qr — QR code to share setup with other devices

🔧 Troubleshooting Quick Reference

Entry — Braking / Turn-In

Issue First Check Then Check

Push — nose won't bite, wide entry Front toe-out (add 0.3–0.5°), front spring (softer) Front ARB (softer), front shock rebound (less), front ride height (lower)

Neutral — good entry, predictable Leave it — don't chase what's working Document baseline shim stack, springs, shocks before tweaking

Loose — rear steps out, rear end light under braking Rear toe-in (add 0.5–1.0°), rear spring (stiffer) Rear ride height (lower), rear shock rebound (less), brake timing (earlier)

Mid-Corner — Cornering / Apex

Issue First Check Then Check

Push — mid-corner understeer, won't hold line Front camber (more negative), front ARB (softer) Front shock position (closer to tower = softer), rear ARB (stiffer), front sway bar

Neutral — holds line through apex Leave it — note this setup as reference Verify camber temps: outside/inside/middle of tire should be even

Loose — rear walks out, can't hold apex Rear camber (more negative), rear toe-in (add 0.5°) Rear ARB (stiffer), rear spring (stiffer), rear ride height (higher)

Exit — Power Down / Acceleration

Issue First Check Then Check

Push — front drags, car won't rotate on power Rear spring (softer), rear ARB (softer) Rear toe-in (reduce 0.5°), front spring (stiffer), reduce drag brake

Neutral — clean exit, full throttle no slip Leave it — verify consistency over 5+ laps Check motor/gear temps, ensure you aren't overheating from excess grip

Loose — wheelspin inside rear, traction roll Reduce punch (ESC), rear toe-in (add 0.5–1.0°) Rear spring (stiffer), rear ARB (stiffer), add anti-squat (0.5mm shim), softer rear rebound

Bumpy / Rough Surface

Issue First Check Then Check

Nervous over bumps — chassis skips Soft damper oil (drop 15–20cSt), bump steer check Spring preload (less), droop (increase), raise ride height 0.5mm

Washes on bumps mid-corner Front shock rebound (less), front spring softer Front ARB (remove), front ride height (lower), front tire insert (softer)

Rear hops / bounces under power Rear shock rebound (less), rear oil weight (lighter) Rear droop (increase), rear tire insert (softer), smooth throttle application

Bottoming out over bumps Raise ride height (0.5–1.0mm), more droop Stiffer springs, less preload, check track for high spots to avoid line

POST /api/v1/quick-tune — Natural language issue → ranked recommendations
POST /api/v1/smart-advisor/recommend — All 5 engines combined (most comprehensive)

✅ Printable Coarse-to-Fine Checklist

□ Step 1: Chassis selected | Shock mount type confirmed (Tower / Shim / Built-in)

□ Step 2: Ride height set: Front ___mm | Rear ___mm | Rake ___mm

□ Step 3: Camber: Front ___° | Rear ___° | Toe: Front ___° | Rear ___° | Caster: ___°

□ Step 4: Springs: Front ___kg/mm | Rear ___kg/mm | ARBs: Front ___ | Rear ___ | Oil: Front ___cSt | Rear ___cSt | Rebound: Front ___mm | Rear ___mm

□ Step 5: Shock: Front angle ___° / MR ___ | Rear angle ___° / MR ___ | Effective spring: Front ___kg/mm | Rear ___kg/mm

□ Step 6: Roll center: Front ___mm | Rear ___mm | Balance: ___% front

□ Step 7: Anti-dive: ___% | Anti-squat: ___%

□ Step 8: Bump steer: Front OK | Rear OK

□ Step 9: Shim stacks documented | Reactive caster set

□ Step 10: ARS configured (if equipped)

□ Step 11: ESC: Timing ___° | Punch ___ | Drag brake ___% | Brake ___%

□ Step 12: Setup sheet printed | Compared to baseline | Lap time prediction saved

Based on 8,000+ real-world setups from IFMAR, ETS, ROAR, and national championships.

User Guide · Back to App · Setup Builder

Shim	Effect
Front tie rod inner	Ackermann
Front tie rod outer	Bump steer (keep minimal: 0.0–0.5mm)
Rear toe link inner	Static rear toe
Rear toe link outer	Rear bump steer

Thickness	Use Case
0.25mm	Fine-tuning, minimum increment
0.50mm	Standard adjustment step
1.00mm	Standard adjustment, most common
2.00mm	Maximum single shim (typical)
2.00–5.00mm	Stacked shims for large changes
0–4.5mm	XRAY T423-T426 top shock mount range

Front Shim	Rear Shim	Effect
Equal (F=R)		Pure caster change, no reactive
Front > Rear		More caster + reactive caster (gains caster under braking)
Rear > Front		Less caster + reverse reactive

Class	Typical Timing	Range
Blinky — Stock 17.5T / 13.5T	40–45°	30–45° mechanical
Blinky — 10.5T	35–40°	25–40° mechanical
Modified	45–55°	35–55° mechanical (max ~55°)

Parameter	Low Grip	Default	High Grip
ESC timing (Modified only)	0° (stock)	5–10°	10–20°
Punch	7–10	4–6	1–3
Drag brake	5–10%	15–25%	15–25%
Brake force	80–100%	50–75%	25–40%

Issue	First Check	Then Check
Push — nose won't bite, wide entry	Front toe-out (add 0.3–0.5°), front spring (softer)	Front ARB (softer), front shock rebound (less), front ride height (lower)
Neutral — good entry, predictable	Leave it — don't chase what's working	Document baseline shim stack, springs, shocks before tweaking
Loose — rear steps out, rear end light under braking	Rear toe-in (add 0.5–1.0°), rear spring (stiffer)	Rear ride height (lower), rear shock rebound (less), brake timing (earlier)

Issue	First Check	Then Check
Push — mid-corner understeer, won't hold line	Front camber (more negative), front ARB (softer)	Front shock position (closer to tower = softer), rear ARB (stiffer), front sway bar
Neutral — holds line through apex	Leave it — note this setup as reference	Verify camber temps: outside/inside/middle of tire should be even
Loose — rear walks out, can't hold apex	Rear camber (more negative), rear toe-in (add 0.5°)	Rear ARB (stiffer), rear spring (stiffer), rear ride height (higher)

Issue	First Check	Then Check
Push — front drags, car won't rotate on power	Rear spring (softer), rear ARB (softer)	Rear toe-in (reduce 0.5°), front spring (stiffer), reduce drag brake
Neutral — clean exit, full throttle no slip	Leave it — verify consistency over 5+ laps	Check motor/gear temps, ensure you aren't overheating from excess grip
Loose — wheelspin inside rear, traction roll	Reduce punch (ESC), rear toe-in (add 0.5–1.0°)	Rear spring (stiffer), rear ARB (stiffer), add anti-squat (0.5mm shim), softer rear rebound

Issue	First Check	Then Check
Nervous over bumps — chassis skips	Soft damper oil (drop 15–20cSt), bump steer check	Spring preload (less), droop (increase), raise ride height 0.5mm
Washes on bumps mid-corner	Front shock rebound (less), front spring softer	Front ARB (remove), front ride height (lower), front tire insert (softer)
Rear hops / bounces under power	Rear shock rebound (less), rear oil weight (lighter)	Rear droop (increase), rear tire insert (softer), smooth throttle application
Bottoming out over bumps	Raise ride height (0.5–1.0mm), more droop	Stiffer springs, less preload, check track for high spots to avoid line