* Axle Ratio: The gear ratio in the differential significantly impacts speed. A lower ratio (numerically higher, e.g., 4.88) will result in lower top speed but greater pulling power. A higher ratio (numerically lower, e.g., 3.55) will allow for higher top speed but less pulling power.
* Tire Size: Larger diameter tires will result in a lower top speed for the same engine RPM.
* Load: A heavily loaded truck will have a significantly lower top speed than an unloaded one.
* Condition of the Engine and Drivetrain: A well-maintained engine will likely reach a higher speed than one in poor condition. Worn components throughout the drivetrain will also reduce top speed.
* Aerodynamics: While not a major factor on a truck of this design compared to other factors, wind resistance will still slightly impact top speed.
While some might claim a theoretical top speed based on engine RPM and gearing, it's highly unlikely someone ever pushed a 1974 F-600 to its absolute maximum speed under ideal conditions. The truck wasn't designed for high speed; its purpose was work. Expect its top speed to be in the 45-65 mph range, but this is just a very rough estimate. The actual speed could be significantly lower or slightly higher, depending on the factors listed above.
