Speed Limiter Removal: How VMAX Maps Work

Why Cars Have Speed Limiters

Almost every modern vehicle has an electronically enforced speed limiter programmed into the ECU. The limiter prevents the vehicle from exceeding a predetermined maximum speed, regardless of the engine’s actual capability.

Manufacturers implement speed limiters for several reasons:

• Tyre safety ratings: The speed limiter matches the vehicle’s OEM tyre rating. A car with V-rated tyres (240 km/h max) shouldn’t exceed that speed, even if the engine can push it further.
• Drivetrain protection: Driveshafts, wheel bearings, and other components have rated maximum speeds. Exceeding them increases the risk of mechanical failure.
• Gentleman’s agreement: German manufacturers (BMW, Mercedes, Audi, Porsche, VW) historically limited most vehicles to 250 km/h (155 mph) as part of an industry agreement. Some have recently moved away from this.
• Insurance and regulation: Some markets require speed limiters at specific thresholds.
• Model differentiation: Lower-spec models may have lower speed limits to differentiate from higher-spec variants that share the same engine and drivetrain.

Common Factory Speed Limits

How Speed Limiters Work in the ECU

The speed limiter is implemented as a torque reduction at maximum vehicle speed. When the vehicle speed (measured by the wheel speed sensors and/or transmission speed sensor) approaches the VMAX value, the ECU progressively reduces the torque output until the vehicle can’t accelerate further.

The VMAX Map

In most ECUs, the speed limiter is a simple parameter or small map:

• Single value (most common): A single constant defining the maximum speed in km/h. Example: VMAX = 250
• 2D map (some ECUs): Maximum speed as a function of gear or driving mode. This allows different limits in different conditions (e.g., lower limit in lower gears).
• Torque reduction curve: Defines how aggressively torque is reduced as speed approaches VMAX. Some ECUs use a progressive reduction (soft approach) while others use a hard cut.

Speed Limiter Implementation Types

Soft limiter (most common):

• As vehicle speed approaches VMAX (typically within 5-10 km/h), torque is progressively reduced
• The driver feels the car gradually losing acceleration
• The car may slightly exceed the VMAX value before torque is fully limited

Hard limiter (less common):

• At exactly VMAX, fuel injection is cut or severely reduced
• The car hits a “wall” — acceleration stops immediately
• More jarring than a soft limiter

Finding the VMAX Map in WinOLS

Using a Mappack/Damos

If you have a Damos or mappack for your ECU, the speed limiter is usually labelled as:

• VMAX or VFMX (Bosch ECUs)
• Vehicle speed limiter or Maximum speed (English mappacks)
• Speed limitation (Continental/Siemens ECUs)

Search the map list for “VMAX,” “speed,” or “velocity.”

Manual Finding

If you don’t have a mappack:

1. The speed limiter is typically a single 16-bit value in the calibration area
2. Convert the known speed limit to the ECU’s internal format:
   • 250 km/h might be stored as 250, 2500 (×10), 6944 (in cm/s), or other scaling
   • Common scalings: km/h × 1, km/h × 10, or km/h × 128/N (where N varies)
3. Search for the hex value in WinOLS (Edit → Search → Value)
4. There may be multiple matches — look for one in the calibration area (not program code)
5. Verify by checking nearby values — the speed limiter is often near other vehicle-specific parameters (tyre circumference, final drive ratio, etc.)

Comparison Method

If you have an original file and a “VMAX removed” file from a file service, compare them. The changed value is your speed limiter.

How to Modify the Speed Limiter

Once you’ve identified the VMAX parameter:

Raising the Limit

Simply change the value to your desired maximum speed. For example, to change from 250 km/h to 300 km/h, replace the value (accounting for scaling).

Effectively Removing the Limit

Set the value to a speed the car can never physically reach — e.g., 350 km/h or 400 km/h. This effectively removes the limiter while keeping the map structure intact. The engine will run out of power long before reaching the set limit.

Things to Check

• Multiple VMAX values: Some ECUs have separate speed limiters for different conditions (gear-dependent limits, forward/reverse limits, etc.). Check all related parameters.
• Torque reduction curve: If the ECU has a speed-based torque reduction curve, ensure it’s adjusted to match your new VMAX — otherwise you may experience reduced power at high speeds.
• Cluster speed limit warning: Some vehicles have a speed warning buzzer (common on Asian vehicles) that’s independent of the ECU’s speed limiter. This may be controlled by the instrument cluster ECU, not the engine ECU.

Safety Considerations

Removing or raising the speed limiter carries real risks:

Tyre Ratings

Your tyres have a maximum rated speed:

Never exceed your tyre’s speed rating. Tyre failure at high speed is catastrophic. If you raise the speed limiter, ensure your tyres are rated for the new maximum speed.

Drivetrain Limitations

• Driveshafts: Have critical speed ratings — vibration at high RPM can cause failure
• Wheel bearings: Generate increasing heat at higher speeds
• Braking capability: Stopping distances increase with the square of speed. Stock brakes may not adequately handle repeated stops from very high speeds.
• Cooling: At very high speeds, the engine, transmission, and differential generate significant heat. Stock cooling systems may not cope with sustained high-speed driving.

Aerodynamic Stability

Not all vehicles are aerodynamically stable at very high speeds. Vehicles with high centres of gravity (SUVs, vans) or poor aerodynamic design may become unstable above their designed maximum speed.

Our VMAX Products

Speed limiter removal is available through:

• Our tuning file database — many files include VMAX removal as a standard option
• Our custom file service — specify VMAX removal alongside your remap order
• INSTATuner — VMAX removal is available as an option when downloading files

Always upgrade to appropriately rated tyres if you intend to drive at speeds above the original limiter.