What Is Sub Trim?

Sub Trim is an electronic adjustment in an RC radio system that changes the neutral center position of a servo without physically moving the servo horn or linkage.

Most RC radios allow Sub Trim adjustments for:
• Steering
• Throttle
• Brake
• Auxiliary channels
• Gyros
• Winches
• Four-wheel steering systems

In simple terms, Sub Trim tells the servo:
“This is your new center position.”

For example:
• If your front wheels point slightly left when the steering wheel on the transmitter is centered, Sub Trim can electronically re-center the steering servo.
• If your throttle linkage is not perfectly aligned at neutral, Sub Trim can correct the servo position.

Sub Trim is primarily used during vehicle setup rather than during active driving.

---

How Does Sub Trim Affect Your Car?

Sub Trim directly affects servo centering and neutral positioning. Even very small adjustments can significantly influence steering precision and throttle feel.

Steering Effects
Improper Steering Sub Trim can cause:
• Vehicle pulling left or right
• Uneven steering throw
• Different turning radius left vs right
• Reduced steering consistency
• Servo binding at full lock on one side (but not the other)

Correct Steering Sub Trim helps:
• Maintain equal steering geometry
• Improve straight-line stability
• Keep the servo centered mechanically
• Reduce unnecessary strain on the servo

This is especially important in:
• Touring car racing
• Carpet racing
• Drift setups
• High-speed speed-run vehicles

Throttle and Brake Effects
Throttle Sub Trim can influence:
• Idle position on nitro vehicles
• Brake drag
• Neutral throttle calibration
• ESC trigger response

Incorrect throttle Sub Trim may cause:
• A vehicle creeping forward
• Constant brake drag
• Inconsistent throttle feel
• ESC calibration issues

On electric vehicles, excessive throttle Sub Trim can also interfere with ESC neutral calibration.

Servo Geometry Effects
Large amounts of Sub Trim can shift servo geometry away from the ideal mechanical center.

This can create:
• Unequal steering throw
• Reduced steering precision
• Different Ackermann characteristics
• Linkage imbalance
• Servo over-travel on one side

That is why experienced racers use:
• Mechanical adjustments first
• Small Sub Trim corrections second

---

How Do You Change Sub Trim?

Most modern radios have a dedicated Sub Trim menu inside the transmitter settings.

Basic Process
Step 1: Power Everything On
Turn on:
• Transmitter
• Vehicle electronics

Allow the servo to center naturally.

Step 2: Set Steering Trim to Zero
Before adjusting Sub Trim:
• Reset Steering Trim to neutral
• Reset throttle trim if necessary

Sub Trim should never compensate for physical trim adjustments.

Step 3: Access the Sub Trim Menu
Navigate to:
• Linkage Menu
• Servo Menu
• Function Menu
• Sub Trim Menu

The exact location depends on the radio brand.

Step 4: Select the Channel
Choose the desired channel:
• CH1 = Steering
• CH2 = Throttle
• CH3+ = Auxiliary functions

Step 5: Adjust the Neutral Position
Increase or decrease Sub Trim until:
• Steering is centered (Sub Trim to 0)
• Throttle rests at neutral (Sub Trim to 0)
• Attach linkages to servo(s)

Step 6: Recheck Endpoints and Linkages
After setting Sub Trim:
• Verify steering endpoints
• Check for servo binding
• Confirm equal steering throw
• Ensure throttle and brake movement remain correct

---

When To Change Sub Trim

Sub Trim should usually be adjusted during vehicle setup, maintenance or electronics installation.

After Installing a New Servo
A new servo may not center identically to the previous one.

Use Sub Trim to:
• Re-center steering
• Correct linkage alignment
• Fine-tune throttle neutral

After Rebuilding Steering Components
Changes to:
• Servo horns
• Bellcranks
• Turnbuckles
• Servo savers
• Linkages

…may require Sub Trim adjustments.

When the Car Pulls Slightly
If the vehicle consistently drifts:
• First inspect mechanical alignment
• Then use small Steering Trim corrections
• Finally use Sub Trim if mechanical centering is incorrect

During Precision Racing Setup
Competitive racers often fine-tune Sub Trim:
• After alignment adjustments
• After ride height changes
• After toe adjustments
• After changing steering geometry

This helps maximize steering symmetry.

For Nitro Idle Setup
Nitro racers sometimes use throttle Sub Trim to:
• Fine-tune idle gap
• Adjust brake neutral
• Maintain stable idle consistency

However, excessive throttle Sub Trim should be avoided and, instead, fixed mechanically.

---

What to Check After Changing Sub Trim

Sub Trim adjustments can affect multiple vehicle systems. Always inspect the following after making changes.

Steering End Point Adjustment (EPA)
Changing Steering Sub Trim can alter:
• Left steering throw
• Right steering throw

Recheck EPA settings afterward.

Servo Binding
Turn the wheels fully left and right.

Look for:
• Servo buzzing
• Linkage tension
• Excessive strain
• Reduced steering smoothness

Binding can damage servos over time.

Steering Symmetry
Check whether:
• Left steering angle equals right steering angle
• Steering wheel returns to center consistently
• The car tracks straight

ESC Calibration
After throttle Sub Trim changes:
• Recalibrate the ESC if needed
• Verify neutral throttle operation
• Ensure reverse engages correctly

Some ESCs are very sensitive to neutral position changes.

Nitro Idle Gap
Nitro vehicles should maintain:
• Proper carburetor opening
• Stable idle RPM
• Correct brake neutral

Improper throttle Sub Trim can affect all three.

Dual Rate and Expo
Large Sub Trim changes may alter:
• Steering feel
• Response timing
• Overall steering balance

Verify that Dual Rate and Steering Curve (Expo) settings still feel correct.

---

Basic Sub Trim vs Advanced Settings

Basic Sub Trim Settings
Basic users typically:
• Center steering
• Correct slight pulling
• Set throttle neutral
• Align steering wheels visually

For most RTR vehicles, small Sub Trim adjustments are sufficient.

Recommended approach:
1. Turn on your radio, followed by the vehicle. Let the servo self-center.
2. Install servo horn as close to center as possible
3. Use linkage adjustments first
4. Use minimal Sub Trim afterward

Advanced Sub Trim Settings
Advanced racers use Sub Trim for:
• Precise steering symmetry
• Equal steering geometry
• Fine throttle positioning
• Multi-servo synchronization
• Drift gyro balancing

High-end racers will:
• Measure steering throw with gauges
• Match left/right steering angle exactly (using linkage)
• Tune servo center response
• Balance steering Ackermann characteristics

In competitive racing, very small Sub Trim changes can noticeably alter handling consistency.

---

FAQ

Q: Is Sub Trim the same as Steering Trim?
A: No. Steering Trim is typically adjusted while driving to correct small directional changes. Sub Trim is a setup adjustment used to electronically center the servo.

Q: Should I use Sub Trim or adjust the linkage first?
A: Always adjust the linkage and servo horn mechanically first. Use Sub Trim only for fine electronic corrections.

Q: Can too much Sub Trim damage a servo?
A: Indirectly, yes. Excessive Sub Trim can create servo binding or uneven steering geometry in one direction, which may overload the servo.

Q: Does Sub Trim affect steering throw?
A: Yes. Large Sub Trim adjustments can change left/right steering balance and affect EPA settings.

Q: Should electric RC cars use throttle Sub Trim?
A: Usually very little. Many ESCs prefer neutral throttle at zero trim and zero Sub Trim for proper calibration.

Q: Does Sub Trim affect gyro performance?
A: Yes. Steering gyros rely on proper servo centering. Incorrect Sub Trim can cause drifting, twitching or inconsistent gyro correction.

Q: How much Sub Trim is acceptable?
A: Small adjustments are ideal. If you need large amounts of Sub Trim, reposition the servo horn or adjust linkage lengths.

Q: Can Sub Trim improve racing consistency?
A: Absolutely. Properly centered steering geometry improves predictability, corner consistency and straight-line stability.

Back to the RC Transmitter Settings Guide.