How the car drives
Goal: find the parts that control acceleration, gears, suspension and grip, then make one change you can compare while driving.
Before you start
Use a working car from Vehicle Setup. Stop Play Mode and save a copy of the scene before tuning.
Select the vehicle root in the Hierarchy, then click a module card to open that part in the Inspector. Settings under Live values report what is happening during Play Mode; they are not the place to author the vehicle.
If an edited value changes back when Play starts, check Assists and Presets before changing it again.
What actually happens when you press the throttle
The drivetrain is the chain that carries engine power to the wheels. Torque is its turning force.
| Part | Plain meaning | Start here for |
|---|---|---|
| Engine | Produces torque from the throttle | Acceleration and RPM |
| Clutch | Connects the engine to the gearbox | Pulling away and interrupting power during shifts |
| Gearbox | Changes how much the engine turns for each wheel rotation | Gear count, ratios and automatic shifting |
| Differential | Splits torque between an axle's wheels | Driven axle and final drive ratio |
| Axles and wheels | Apply steering, braking and drive force at the road | Suspension and tire grip |
The wizard connects this chain for you. If you built a car by hand, check its Power output connections and each differential's Connected axle.
1. Find the setting for your change
| You want to change | Select | Setting |
|---|---|---|
| How strongly the engine pulls | Engine | Max torque |
| Gearing for a target top speed | Engine | Top speed, with Auto-calculate differential ratio on |
| Automatic or manual shifting | Gearbox | Transmission |
| How long a gear change takes | Gearbox | Shift time |
| Which axle receives power | Diff | Connected axle |
| Bouncing after a bump | A wheel collider | Damper under Suspension |
| Body movement on its springs | A wheel collider | Spring under Suspension |
| Tire grip | An RCCP wheel collider | Grip |
| Braking strength | An axle | Brake torque and Brake share |
Check: you can locate the setting and its tooltip. Note its original value before editing.
2. Make one change and compare it
- Choose one row above.
- Make a small change with Play Mode stopped.
- Press Play and repeat the same driving task on the same road: a standing start, a straight braking test, or the same corner.
- Record what changed. For example, compare speed after the same amount of time, or how many times the body bounces after the same bump.
- Stop Play Mode. Keep and save the change if it helps; otherwise restore the original value.
Check: you can describe the difference caused by this one setting. Changing several settings together makes that comparison difficult.
Setting the car's top speed
With Auto-calculate differential ratio on, RCCP calculates the differential's Differential ratio using the target Top speed, engine RPM, top gear and wheel size. It recalculates when the engine component initializes and when the target speed changes.
This sets gearing for the requested speed; the road, grip and available engine power still affect the speed you reach.
Turn automatic gearing off if you want to author Differential ratio yourself. A higher ratio gives more torque at the wheels but less road speed at a given engine RPM.
The optional Limiter module provides Speed limit per gear. This is a separate speed cap, not a replacement gear ratio.
When the car changes gear
Transmission selects manual, automatic or automatic DNRP operation. DNRP means Drive, Neutral, Reverse and Park.
For automatic shifting, start with these settings:
| Setting | What it controls |
|---|---|
| Shift up RPM | Engine speed needed for an upshift |
| Shift-up timing | The fraction of the gear's target speed needed for an upshift |
| Shift down RPM | Engine speed at which a lower gear is requested |
| Cool-down between shifts | A pause that prevents immediate repeated shifts |
An upshift needs the RPM condition and both road speed and wheel-derived speed to reach the speed threshold. If the engine stays at the limiter, check both conditions. If it repeatedly shifts up and down, check the gap between the upshift and downshift RPM settings.
Gear-ratio preset buttons in the gearbox Inspector provide starting sets. Auto throttle on shifts adds RPM matching during shifts; tune that after normal shifting works.
With an automatic clutch, both automatic transmission modes can recover from an abrupt stop at 10 km/h or less even if held throttle keeps the engine above Shift down RPM. The gearbox selects a lower gear suitable for road speed, checks that driven-wheel RPM is safe for that gear, and keeps the normal shift delay and cooldown. Recovery applies only in a forward gear; manual control, neutral, park and reverse are preserved.
How hard the engine pulls
| Setting | Meaning |
|---|---|
| Max torque | Overall engine turning force |
| Max torque RPM | Engine speed at which the torque curve peaks |
| Idle RPM / Max RPM | The engine's operating range |
| Engine inertia | Resistance to changing engine speed |
| Auto-create torque curve | Builds a curve from the engine settings |
| Engine braking strength | How strongly the engine slows the car after you release the throttle |
| Turbocharged | Enables turbo boost; its boost and torque multiplier settings shape the extra power |
With automatic torque-curve creation off, Torque curve becomes editable. Its horizontal axis is RPM and its vertical axis is a fraction of Max torque.
Front-wheel, rear-wheel or four-wheel drive
A differential drives the axle assigned to Connected axle.
| Layout | Connections |
|---|---|
| Front-wheel drive | One differential connected to the front axle |
| Rear-wheel drive | One differential connected to the rear axle |
| Four-wheel drive | A differential for each driven axle |
The axle's Powered axle readout is set by the differential. Use the connection to choose the layout.
Torque share on an axle scales its drive contribution. Differential type changes the left/right torque split: Open reacts to wheel-speed difference, Limited reduces that effect according to its limited-slip setting, and Full locked and Direct use an equal torque split in this implementation. Equal torque does not guarantee equal wheel speed on different surfaces.
Making the suspension softer or stiffer
Each wheel has Unity suspension settings:
| Setting | What to look for |
|---|---|
| Suspension travel | Enough movement for the bumps the car crosses |
| Spring | Enough support for the vehicle without excessive movement |
| Damper | A controlled return after a bump |
| Rest position | Where the suspension aims to sit within its travel |
Compare the left and right wheels of the same axle when editing. A behavior preset can multiply the base Spring and Damper values.
Anti-roll force on each axle reduces the difference in suspension movement between its wheels. If the whole car tips over, also inspect its center of mass and physical wheel spacing; see Tuning Recipes.
Making the tires grip more or less
Grip on each RCCP wheel scales the friction supplied by the ground surface. Start there before editing friction curves.
The wheel also has Forward grip for acceleration and braking and Sideways grip for cornering. Their curves describe grip as slip increases: Peak-grip slip, Peak grip, Sliding slip and Sliding grip.
A behavior preset can replace these curves. RCCP also updates Unity's grip stiffness fields during driving, so use RCCP's Grip or the ground surface settings for those changes.
If the change does not work
| What you see | What to check |
|---|---|
| Engine revs, car stays still | Gear state, clutch state, drivetrain connections, grounded wheels and brakes |
| A live torque readout is zero | It may be normal in neutral or while shifting. Compare the chain while actively driving in gear. |
| Final drive keeps changing back | Turn off automatic gearing before editing that ratio manually. |
| Handling settings change back | Check the active behavior preset. |
| Changing wheel appearance does not change grip | Camber, caster and rim offset position the visible wheel; use Grip for tire friction. |
| A car is still slow after raising Top speed | Check power, gearing, surface grip and the Limiter module. |
Read next
- Tuning Recipes — choose a test from a specific symptom.
- Assists and Presets — control shared handling settings.
- Field Reference — detailed fields, types and tooltips.