🏎️ RC Tuner

Module 3 · The Suspension Backbone

🔩 Springs & Damping

Spring rate, oil weight, preload — learn what each does and how to pair them.

Lesson 1 of 5

🌀 Spring Rates — Stiffness Explained

Springs rated in N/mm (or kg). Higher = stiffer. Rate affects weight transfer SPEED and amount.

Spring rate determines how much force it takes to compress the spring 1mm. A 5.0 kg spring (49 N/mm) needs 4.9N to move 1mm. A 3.0 kg spring (29 N/mm) needs only 2.9N.

Typical 1/10 touring rates:

Front: 3.5 – 5.0 kg · Rear: 3.0 – 4.5 kg

Soft springs → more body roll, better on bumpy tracks, slower weight transfer. Hard springs → less roll, sharper response, more aggressive but less forgiving.

Spring rate explorer — drag to see effects

Front stiff, rear moderate. Balanced for most tracks. Slight understeer bias for stability.
💡 Track selection guide
🟢 Smooth/high-grip (carpet): Stiffer (4.5+ front) — car responds instantly
🟡 Medium (indoor asphalt): Moderate (3.8-4.2 front) — balanced
🔴 Bumpy/low-grip (outdoor): Softer (3.2-3.6 front) — absorbs irregularities
Lesson 2 of 5

💧 Shock Oil — Controlling Speed

Oil viscosity (cSt) determines how FAST weight transfers. Temperature changes everything.

Thicker oil = slower weight transfer = more stable but less responsive. Thinner oil = faster weight transfer = more agile but less predictable.

Typical weights:

Front: 300–500 cSt · Rear: 250–400 cSt

Temperature effect: Oil viscosity changes ~3-4% per °C. A 400 cSt oil at 20°C becomes ~280 cSt at 40°C. That's a HUGE change after 5 laps.

Temperature vs viscosity — the hidden variable

Your shock oil at 400 cSt (rated at 25°C):
15°C (cold day)~600 cStVery stiff
25°C (rated temp)~400 cStBaseline
35°C (after 3 laps)~260 cStGetting soft
45°C (hot track)~170 cStMuch softer
⚠️ This is why summer ≠ winter setups

Track temp 10°C colder? Oil is effectively 50% thicker. You'd want ~100-150 cSt LESS oil in winter to get the same feel.

Quick check

After 5 laps on a hot track, how does the oil behave?
Lesson 3 of 5

🔧 Preload — Sets Ride Height, NOT Stiffness

The most misunderstood adjustment in RC. More preload doesn't make the spring stiffer.

Myth: "Compressing the spring more makes it stiffer." FALSE.

Spring rate is fixed by the wire thickness, number of coils, and material. Preloading (compressing) the spring just changes where in its travel the spring starts supporting the car's weight.

What preload actually does:

1. Sets ride height (along with spring rate)
2. Determines how much 'free travel' the wheel has before the spring engages
3. Affects how progressive the suspension feels

Preload truth table

✓ More preload DOES:
  • Increases ride height
  • Reduces available down-travel
  • Makes spring engage sooner over bumps
  • Reduces 'pack' (hitting shock bottom)
✗ More preload does NOT:
  • Make spring stiffer
  • Change weight transfer amount
  • Affect damping rate
  • Change how much load tire supports
🎯 Correct adjustment order
  1. Spring rate — sets the car's overall stiffness character
  2. Oil weight — sets damping speed
  3. Preload — fine-tunes ride height (with droop)
  4. Droop — sets suspension travel range
Lesson 4 of 5

🎯 Front-Rear Pairing — The Seesaw

What you do to the front REQUIRES compensating the rear. Balance is relational.

Your car is a seesaw on two fulcrums. Front stiffer relative to rear = more front grip bias (resists understeer). Rear stiffer = more rear grip bias (can cause oversteer).

The golden pairing rule: Front should typically be slightly stiffer than rear (by 0.3-0.5 kg). This gives a stable platform with gentle roll balance.

Common pairings by track style

🟢 Neutral — Most tracks
Front: 4.0 kg + 400 cSt · Rear: 3.5 kg + 300 cSt
Balanced. Good starting point for unknown tracks.
🔵 Smooth / High-grip
Front: 4.5 kg + 450 cSt · Rear: 4.0 kg + 400 cSt
Sharp response. Car needs less help from suspension to find grip.
🟡 Bumpy / Low-grip
Front: 3.5 kg + 300 cSt · Rear: 3.0 kg + 250 cSt
Softer, absorbs bumps. Car keeps tires on ground better.
🔴 Aggressive — Rotates hard
Front: 3.8 kg + 350 cSt · Rear: 3.5 kg + 250 cSt
For tight tracks. Rear softer/thinner oil = more rotation. Experienced drivers only.
Lesson 5 of 5

🚨 Diagnosing Suspension Issues

Bouncy, wallowing, or crashing through bumps? Learn to identify and fix the right problem.

Each symptom maps to a SPECIFIC cause. Don't randomly change settings — diagnose first.

The Big Three:

• Bouncy (wallowing): Oil too thin OR blow-by (bad seals)
• HARSH/crashing: Oil too thick OR spring too stiff
• Pack/bottom out: Not enough preload OR oil too low

Diagnostic challenge — match symptom to fix

Car bounces/wallows after hitting bumps — doesn't settle fast enough.
Car crashes/harshly transmits small bumps — never settles.
Shock bottoms/packs on big bumps — clunk sound.
Course Hub

🏁 Module 3 Complete!

You've mastered springs, oil, preload, pairing, and diagnosis. Time for the real physics: roll centers and shims.

Start Module 4: Roll Center & Shims →