Acceleration Delay
Controls the programmed acceleration rate. A higher value normally produces a more gradual increase in speed.
Driving Dynamics Workshop
Accelerate · Brake · Shunt · Measure
Acceleration & Braking Delay | Set CV3 & CV4
A heavy freight locomotive should not leap away like a railcar. A shunting locomotive, on the other hand, needs to respond quickly to the controller. CV3 and CV4 allow digital driving dynamics to be matched to the vehicle, train type and layout.
This workshop connects CV values with measurable times and stopping distances, explains shunting mode, switchable momentum, sound, braking sections and constant stopping distances, and shows why the same values can behave differently with different decoders.
CV 3
acceleration delay
CV 4
braking delay
F4?
often momentum off – check mapping
0.896 s
DCC reference factor
Acceleration
Increase CV3
A higher value usually means slower, longer acceleration →
Braking
Increase CV4
A higher value usually means a longer braking period →
Stopping Point
Time Is Not Stopping Distance
The initial speed significantly changes the distance travelled →
Jerky Locomotive
Do Not Hide It with CV3
Check the mechanism and motor control first →
Digital Momentum Instead of an Abrupt Start
What Do Acceleration and Braking Delay Actually Do?
A locomotive decoder receives a requested speed step from the digital command station. Without programmed momentum, it attempts to reach the new target relatively quickly. That may work technically, but the sudden change in speed often looks unnatural on a model railway.
The acceleration delay defines how quickly the decoder's internal target rises from a lower to a higher speed. In the standard DCC system this basic function is controlled by CV3. The braking or deceleration delay works in the opposite direction and is configured with CV4.
Both settings are independent. A shunting locomotive can use a short acceleration time and short braking time. A heavy freight locomotive can build up speed gradually and coast for much longer. With a sound decoder, engine revving, load changes, idle sounds and brake effects should also match the visible movement.
It is important to distinguish this from motor control . If a locomotive already jerks at speed step 1, a high CV3 value does not repair the technical cause. Reliable current collection, a free-running mechanism, suitable starting voltage and stable load control must come first.
Seconds and Centimetres Instead of Guesswork
Driving Dynamics Workshop: Estimate CV Time and Stopping Distance
These calculators deliberately provide reference values rather than guaranteed results. Under the standard DCC calculation, the acceleration or deceleration rate is based on 0.896 seconds multiplied by the CV value and divided by the number of speed steps in use. Across the complete speed-step range this corresponds approximately to CV value × 0.896 seconds. Manufacturers can nevertheless use different scaling, internal speed steps, soft-start ramps or additional braking functions, so the factor can be adjusted below.
Convert CV3 / CV4 to Time
Calculates an approximate full-range acceleration or braking time.
13.44 Seconds
Approximate full-range DCC reference for CV value 15.
Whenever possible, use the actual factor and behaviour described in the manual for the exact decoder family.
Convert a Required Time to a CV Value
Useful when a locomotive should take approximately a defined number of seconds to reach its configured maximum speed.
Starting Value Approximately CV 13
Fine-tune the result with a test run on the layout.
The value range and scaling defined by the decoder manufacturer remain authoritative.
Estimate Model Stopping Distance
Approximation for uniform deceleration from a specified prototype speed to a complete stop.
Approx. 191.6 cm Model Stopping Distance
Physical approximation assuming uniform deceleration.
Decoder speed curves, actual model speed, flywheel, gradient, train load and rolling resistance can all alter the real stopping distance.
The Most Important Driving-Dynamics Variables
CV 3
CV 4
CV 23
CV 24
CV 5
F4?
ABC
cm
Understanding CV3 and CV4 Correctly
Braking Delay
Controls the programmed deceleration rate. The value does not define a fixed stopping distance in centimetres.
Acceleration Adjustment
Optional NMRA adjustment used to add to or subtract from the basic acceleration rate, for example when adapting momentum for different train loads or consists. Decoder support must be checked.
Deceleration Adjustment
Optional adjustment corresponding to CV23 for the braking rate. Its practical implementation and support depend on the decoder.
Maximum Speed
On compatible decoders, set this sensibly before final braking tests because a higher speed increases the distance travelled during the same braking time.
Momentum Override
Many decoders traditionally use a function button to disable acceleration and braking momentum. F4 is common, but the actual button may be changed through function mapping.
Braking Section
Compatible DCC decoders can detect an asymmetrical DCC track signal. The braking parameters used are manufacturer-specific.
Constant Stopping Distance
Some modern decoders provide a dedicated stopping-distance function. This is not the same as the time-based delay controlled by CV4.
Vehicle Type Instead of One Universal Value
Shunting
Branch Line
Passenger Train
Heavy Load
Steam & Sound
Multiple Unit
Which Driving Dynamics Suit Which Train?
Universal CV values are rarely useful. Convincing driving behaviour should reflect the vehicle type, train mass, operating purpose and available track length.
Shunting Locomotive
Short acceleration and braking times. A switchable momentum override or easily accessible shunting mode is particularly useful for precise coupling movements.
Railcar
Brisk but not abrupt acceleration. Choose braking behaviour that allows short platforms and frequent stops to be reached reliably.
Express Locomotive
Medium to longer acceleration. Set a realistic maximum speed first and then fine-tune CV4.
Freight Locomotive
Gradual load take-up, long acceleration and controlled coasting make the mass of a heavy freight train much more convincing.
Steam Locomotive
Tune visible acceleration and the sound sequence together. Exhaust beats, load changes and brake effects should match the movement.
Two Locomotives
Match the speed curves first. Then adjust acceleration and braking times so that both locomotives behave as similarly as possible.
From a Test Locomotive to a Convincing Train
1
2
3
4
5
6
7
8
Fine-Tune Acceleration and Braking Delay in Eight Steps
Identify the Decoder
Check the manufacturer, decoder family and instructions. Record the permitted value range, time factor and additional momentum functions.
Check the Locomotive Technically
Test with very little programmed momentum. The locomotive must already run smoothly and evenly without a long acceleration delay.
Set the Maximum Speed
Excessive model speed distorts every stopping-distance measurement carried out afterwards.
Mark a Test Section
Define a starting point, measuring point and stopping point. Always compare settings under the same conditions.
Configure CV3
Increase the value gradually until the acceleration suits the vehicle class and normal train load.
Fine-Tune CV4 Separately
Start braking from the same speed every time and measure the actual stopping point.
Test Shunting Mode
Check momentum override, shunting speed and function buttons during real coupling and yard movements.
Save the Values
Record the locomotive address, decoder, CV3, CV4, maximum speed, momentum button and any special settings.
Time Delay Is Not Stopping-Point Control
Why Does CV4 Not Always Stop the Locomotive at the Same Point?
CV4 fundamentally creates a time-based deceleration. If a reproducible stop in front of a signal or platform is required, the initial speed and braking system must also be controlled.
Initial Speed
A faster train covers more distance during the same braking period. The same CV4 value therefore does not automatically produce the same stopping point.
ABC Braking
Compatible DCC decoders can detect an asymmetrical track signal. Depending on the decoder, the normal CV4 delay or a separate braking-distance function may be used.
Constant Stopping Distance
Some decoders provide a dedicated function for more reproducible stopping distances. Separate parameters and, in some cases, calibration procedures apply.
DC / Märklin Braking Sections
Multi-protocol decoders may support additional braking methods using DC voltage or special signal sections.
Train Load
The decoder controls the motor, but flywheel effect, gearbox characteristics, wagon resistance and gradients influence the visible movement.
Computer-Controlled Operation
Automated layouts can use feedback detectors and software speed profiles. Decoder momentum then needs to be coordinated with the layout-control system.
Decoder Family Determines the Details
Manufacturers of Drive Decoders, Sound and Programming Equipment
CV3 and CV4 are widely supported. Additional momentum profiles, function-button assignments, constant stopping distances and programming tools can nevertheless differ considerably.
Check Manufacturer-Specific Additional Momentum Ramps
Example: PIKO SmartDecoder XP
CV3 and CV4 Can Interact with an Additional Soft-Start and Braking Ramp.
PIKO documents an additional soft-start and braking ramp controlled through CV53 on suitable SmartDecoder XP families. If changes to CV3 and CV4 appear to have little effect, check the exact decoder documentation and firmware first. Current XP firmware also provides a prioritisation setting allowing the decoder to prioritise either the soft-start ramp or the CV3/CV4 acceleration and braking delay. Never transfer these PIKO-specific settings to other decoder families.
Decoders with Fine-Tunable Driving Behaviour
Locomotive Decoders for H0, TT and N
ESU · H0 · PluX22
LokPilot 5 DCC
DCC locomotive decoder with extensive motor-control settings and several supported braking methods.
View Product →
PIKO · H0 · Multi-Protocol
SmartDecoder XP 5.1
Modern multi-protocol decoder with extensive driving, braking and configurable momentum functions.
View Product →
ESU · TT/N · Next18
LokPilot 5 micro
Compact multi-protocol decoder for small vehicles and restricted installation spaces.
View Product →
ZIMO · TT/N · NEM 651
MN150N
Very compact decoder for TT and N vehicles with limited installation space.
View Product →
From the Smallest Locomotive to the Garden Railway
Fine-Tune Acceleration and Braking Delay by Gauge
| Gauge World | Typical Challenge | Recommended Driving Test |
|---|---|---|
| Z Gauge | very short layout distances and sensitive current collection | use small value changes, clean track and sufficient safety distance |
| N Gauge | long trains on a compact layout | test the stopping distance using the longest train operated regularly |
| TT / TTe | shunting and main-line operation on the same layout | test momentum override and normal main-line settings separately |
| H0 / H0e / H0m / H0f | very different vehicles, decoders and train types | select values by vehicle class instead of using one setting for the whole fleet |
| Gauge 0 | strong visual vehicle mass and many additional functions | tune sound, digital couplers and braking sounds together |
| Gauge 1 | large vehicles and long visible coasting distances | use a long test section and sufficient safety margin before the end of the track |
| G Gauge | heavy trains, gradients and changing loads | test with both light and heavy trains and on gradients |
Interpret the Symptoms Correctly
Common Problems with CV3 and CV4
The Locomotive Responds Immediately Despite a High CV3
Check whether momentum has been disabled using a function button or whether an additional decoder function is taking priority over the normal CV3/CV4 ramp.
The Stopping Distance Is Much Too Long
First reduce an unrealistically high maximum speed. Then reduce CV4 and test again from exactly the same initial speed.
The Locomotive Does Not Stop Reproducibly
A purely time-based delay does not guarantee an identical stopping point. Check a braking section or dedicated constant stopping-distance function.
The Locomotive Jerks During Acceleration
Temporarily reduce CV3 and check current collection, gearbox, starting voltage and motor control.
Brake Squeal Is Missing
Sound projects often require a particular speed, sufficiently strong deceleration or speed step 0 before the braking sound is triggered.
Two Locomotives Fight Each Other in a Consist
Match minimum and maximum speeds, speed curves, CV3 and CV4 of both locomotives as closely as possible.
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Decoders, Command Stations and Programmers for Driving Dynamics
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Fine-Tune the Complete Driving Behaviour
From CV3 and CV4 to Convincing Locomotive Control
Acceleration and braking are only two parts of a convincing digital locomotive setup. A well-configured model also needs a suitable maximum speed, smooth motor control, sensible function assignments, an appropriate sound project where fitted and reliable current collection.
Frequently Asked Questions from the Driving Dynamics Workshop
FAQ About Acceleration and Braking Delay
Which CV Controls the Acceleration Delay?
On DCC locomotive decoders, the standard acceleration delay is normally configured with CV3. Manufacturers may additionally provide separate soft-start ramps or alternative momentum profiles.
Which CV Controls the Braking Delay?
The standard DCC braking or deceleration delay is normally configured with CV4. Under the usual interpretation, a higher value produces a longer deceleration period.
What Does Value 0 Mean in CV3 and CV4?
Under the standard DCC definition, value 0 means that no programmed acceleration or braking momentum is applied. Additional decoder functions can nevertheless affect the behaviour.
Which Values Are Realistic for a Locomotive?
There is no universal CV value. Decoder scaling, vehicle type, maximum speed, train load and available layout length all matter. Tune the locomotive by measured time and visible behaviour.
How Long Is the Delay with CV3 Set to 10?
Under the standard DCC full-range reference calculation using 0.896 seconds per CV value, CV3 = 10 corresponds to approximately 8.96 seconds. Manufacturers can use different scaling or additional ramps.
Why Does the Stopping Distance Increase at Higher Speed?
CV4 fundamentally creates a deceleration period. A faster vehicle travels farther during the same amount of time.
Can Acceleration and Braking Momentum Be Disabled with a Function Button?
Many decoders support a momentum override. F4 is commonly used by tradition, but the actual function button may be assigned differently through function mapping.
What Is the Difference Between Shunting Mode and Momentum Override?
Shunting mode normally reduces the maximum speed or changes the usable speed-step range. Momentum override removes the programmed acceleration and braking delay. Both functions can be available independently or together.
How Can I Achieve a Constant Stopping Distance?
A constant stopping distance is an additional decoder function and is not created solely by CV4. Required parameters and any calibration procedure are manufacturer-specific.
Does CV4 Also Apply in an ABC Braking Section?
This depends on the decoder and its configuration. Some decoders use the normal braking delay while others use separate stopping-distance or braking parameters.
Why Does the Locomotive Still Jerk Despite a Long Acceleration Delay?
Check current collection, mechanism, starting voltage and motor-control parameters. CV3 is a momentum setting and cannot repair a technical fault.
How Do I Match Two Locomotives for Double Heading?
First match minimum, mid-range and maximum speed. Then adjust CV3 and CV4, or the measured acceleration and braking times, so that both locomotives behave as similarly as possible.
Driving Dynamics Fine-Tuned? Now Perfect the Entire Locomotive.
The comprehensive Model Railway Guide covers decoders, digital command stations, motor control, sound, track, vehicles, maintenance and layout planning.