Tutorial Adjusting or Removing Speed Limiters

Road-hog123

An Orange Bus
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Firstly it is important to understand that the reason a bus reaches a maximum speed may not be that it is limited. For example, none of the default buses are limited, but will all max out at about 72 km/h. This is because the engines reach "rated RPM" at 2200 rpm and reduce their power output to nothing to prevent engine damage as a result of over-speeding - so when they reach rated RPM in top gear they will stop accelerating. To get a higher top speed you will need to adjust the engine and/or gearbox, which is not the subject of this tutorial.

If instead the bus reaches a speed where it stops accelerating below rated rpm, possibly even having not used all of the gears in the gearbox, then the bus has a speed limiter. This is the case in many buses including the Citybus 400, with the London variant being limited to 39 mph and the Regional to 60 mph.

There are multiple methods used to fit speed limiters to a bus, so instead of a catch-all explanation we have a list of methods. The below list will tell you which method your bus uses - if it's not on the list then check each of the methods to see if it applies.

  • Citybus 400 Regional - Method 1
    • engine_constfile_E40D_Euro5.txt
  • winsome's HK Enviro500MMC - Method 2
    • engine_constfile_ISL8.9E5340B.txt (variants with 70 kph limiter)
    • engine_constfile_ISL8.9E5340B_100.txt (variants with 100 kph limiter)
  • Lowlander's Volvo Olympian 10.4m - Method 2
    • engine_constfile_D86.txt
  • Gx7767's HK 12 metre B9TL - Method 4 (70 kph primary limiter), Method 3 (85 kph secondary limiter)
    • engine_constfile_AVBWU.txt
  • Gx7767's HK Enviro200 - Method 4
    • engine_constfile_ISB6.7_AAU.txt
  • FU482's HK Enviro500 Facelift (Looks like an MMC, isn't an MMC) - Method 4
    • engine_constfile_D92_ZF_D28_turbo.txt

Method 1
Inside the Script folder, or one of it's sub-directories, find the constfile listed after the bus you are modifying. Inside it you will find a definition that looks somewhat like this:
Code:
[newcurve]
speedgov
[pnt]
96
1
[pnt]
97
0
This defines a series of points on a graph which sets the maximum throttle position at particular road speeds. This is taken from the C400R, where you can see that the throttle is allowed to be wide-open (1) at any speed up to 96 km/h. Between 96 and 97 km/h it decreases linearly to fully closed (0) and then remains closed at higher speeds. This means that upon reaching 96 km/h (60 mph) the torque output of the engine will reduce to 0, preventing further acceleration except by downhill slope.

To adjust the speed at which the speed limiter kicks in, adjust the top numbers. For example, this would limit the bus to 40 mph (64 km/h):
Code:
[newcurve]
speedgov
[pnt]
64
1
[pnt]
65
0
To remove the limiter entirely, simply remove the second point definition, such that the graph is a straight line at wide-open throttle.


Method 2
Inside the Script folder, or one of it's sub-directories, find the constfile listed after the bus you are modifying. Inside it you will find a definition that looks somewhat like this:
Code:
[newcurve]
governor
[pnt]
-100
1
[pnt]
69
1
[pnt]
71
0
Please see Method 1 for details on how to change this speed limiter, replacing each instance of speedgov with governor.


Method 3
Inside the Script folder, or one of it's sub-directories, find the constfile listed after the bus you are modifying. Inside it you will find a definition that looks somewhat like this:
Code:
[newcurve]
max_speed
[pnt]
84
1
[pnt]
85
0
Please see Method 1 for details on how to change this speed limiter, replacing each instance of speedgov with max_speed.


Method 4
Inside the Script folder, or one of it's sub-directories, find the constfile listed after the bus you are modifying. Inside it you will find a single-value constant called speedgov.
Code:
[const]
speedgov
70
This is simply the speed in km/h at which the limiter kicks in. Setting a value higher than the bus can reach effectively disables the limiter.
 
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