Balancing grip, droop, damping, and diffs for unpredictable terrain transitions.
Mixed‑Surface Overview
Mixed‑surface rally stages combine hard‑pack tarmac, compacted dirt, and loose gravel. Your setup must deliver predictable behaviour as grip changes rapidly.
Key goals:
- Maintain stability on hard sections
- Preserve traction on loose sections
- Avoid sudden chassis reactions during transitions
Ride Height & Droop
Mid‑range ride height
- Enough clearance for gravel
- Low enough for stability on tarmac
- Maintain a neutral chassis attitude to prevent pitching during surface transitions
Balanced droop
- Front: medium droop for bump absorption
- Rear: medium‑long droop for traction
- Avoid extreme droop — causes chassis pitch on hard surfaces
Target behaviour
- Car should settle quickly after bumps
- No excessive chassis roll entering tarmac sections
- Keep weight transfer controlled so the car stays composed when grip increases suddenly
Damping & Spring Rates
Damping (Shock Oil)
- Front: 450–500 cSt
- Rear: 400–450 cSt
- Adjust ±50 cSt depending on surface ratio
Springs
- Front: medium
- Rear: soft‑medium
- Aim for compliance without bottoming out
Why this works Medium damping prevents harsh reactions on tarmac while allowing enough movement for gravel.
Tyres & Inserts
Tyre Choice
- Medium compound hybrid tread
- Shallow blocks for loose sections
- Smooth centre for hard‑pack stability
Insert Density
- Medium‑density inserts
- Balanced compression for transitions
- Avoid firm inserts — too reactive on gravel
Temperature Control
- Maintain consistent tyre temperature
- Overheated tyres lose grip on tarmac
- Cold tyres lose bite on gravel
Differential Setup
Centre Diff
- 5 000–7 000 cSt
- Balanced power delivery between surfaces
Front Diff
- Slightly thicker (7 000–10 000 cSt)
- Stability under braking on hard sections
Rear Diff
- Thinner (3 000–5 000 cSt)
- Helps rotation on loose terrain
Goal Predictable corner entry on tarmac + controlled rotation on gravel.
Chassis Balance & Weight Distribution
Neutral balance
- Avoid front‑heavy setups — unstable on gravel
- Avoid rear‑heavy setups — twitchy on tarmac
Ballast
- Add 10–15 g near rear diff if traction loss occurs
- Keep ballast low to reduce chassis roll
Electronics
- Ensure battery and ESC are firmly secured
- Movement during jumps destabilises transitions
Steering & Geometry
Toe
- Front: slight toe‑out (0.5–1°) for turn‑in
- Rear: neutral or slight toe‑in for stability
Camber
- Front: –1.5°
- Rear: –1°
- Balanced for mixed grip levels
Caster
- Medium caster (8–10°)
- Helps stability on tarmac and bite on gravel
Driving Technique Tips
- Smooth throttle modulation across surface changes
- Brake early before transitions
- Avoid abrupt steering inputs
- Let the car settle before accelerating
- Prioritise consistency over outright speed
