Theory of Operation
The ISM Road Speed Governor controls how fast the vehicle may travel on level ground. This feature is always on. Using Droop settings, the feature can be tailored to provide desired performance, fuel economy and speed control.
Optimal Droop Settings
Droop settings are used to control how the Road Speed Governor performs on grades. Droop is defined as the rate of change when approaching the maximum control limit.
The Accelerator Lower Droop setting is used to control how your engine operates on downhill grades. It controls fueling as you drive down a grade. It may be set be at 0, 1, 2, or 3 MPH depending on desired performance and speed control. If you wish to limit fueling at your maximum vehicle speed it should be set to 0 MPH. Settings of 1, 2, or 3 MPH will allow the engine to give extra fueling 1, 2, or 3 MPH above the maximum vehicle speed. This lets you increase maximum vehicle speed in anticipation of the next grade, but reduces speed control. Higher settings result in better performance, but less speed control.
The Accelerator Upper Droop setting is used to control how your engine operates on uphill grades. It controls fueling as you drive up a grade or accelerate to your maximum vehicle speed. It may be set be at 0, 1, 2, or 3 MPH depending on desired performance and economy. If you desire maximum performance it should be set to 0 MPH. This means your engine will receive maximum fueling until it reaches the maximum vehicle speed setting. Settings of 1, 2, or 3 MPH will limit fueling at 1,2, or 3 MPH below the maximum vehicle speed. This has positive impact on fuel economy, but will slightly reduce maximum vehicle speed during hill climbing. Higher settings result in better fuel economy, but reduced performance.
Upper Droop Performance vs. Fuel Economy
Lower Droop Performance vs. Speed Control
Best Performance No Fuel Economy Benefit
Best Speed control No performance Benefit
Good Performance Slight Fuel Economy Benefit
Good Speed Control Slight Performance Benefit
Fair Performance Moderate Fuel Economy Benefit
Fair Speed Control Moderate Performance Benefit
Reduced Performance Best Fuel Economy Benefit
Reduced Speed Control Best Performance
The Upper and Lower Droop settings for the Road Speed Governor and Cruise Control features are designed alike. Road Speed Governor and Crusie Control Droops can be set up independently and differently. Remember, the features will not operate exactly the same way if they are setup differently.
In summary, Upper Droop settings provide a tradeoff between performance and fuel economy and Lower Droop settings provide a tradeoff between performance and speed control.