Other than the cost factor between gas and diesel motorhomes, what are we really talking about when it comes down to gas versus diesel? Say for example in a truck you want to use to pull a trailer. This is where we need to factor in the engine itself. This is also where torque and horsepower come into the equation.
Explaining torque and horsepower can get extremely technical, and we want to keep this simple and easy to understand. With that said, torque is basically the force or energy required to move something. Torque is the measurement of force, and force is measured in reference to a twisting or rotating shaft. In English terms torque is measured in pounds-feet, but is more commonly referred to as foot-pounds. So in keeping it simple let’s just say that torque can be thought of as the amount of turning force it takes to move one pound of weight the distance of one foot.
Torque can be multiplied through gear ratios. You have probably heard that the higher the real axle gear ratio is the better the truck will tow. The axle ratio is the number of times the driveshaft must rotate to turn the rear wheels one time. If you have a 3.73:1 axle ratio the drive shaft turns 3.73 times for each full turn of the axle. So in a sense torque really equals towing capacity.
Horsepower on the other hand is torque X RPM’s. Torque is how much work is being done, and horsepower is how fast you get the actual work done. What’s interesting is an engine rated at 350 horsepower only produces that horsepower at a rated peak power RPM. This RPM range, for a gasoline engine, is often between 5,000 and 6,000 RPM’s. When an engine is idling the horsepower is significantly lower, and as the RPM’s raise so does the horsepower. When you are towing a trailer the engine speed is more likely to be in the low to mid 2,000 RPM range, which means you probably have slightly more than half of the rated horsepower. Horsepower is measured by a dynamometer. A dynamometer puts a load on the engine and measures the amount of power the engine produces against the load at various speeds. In reality it is measuring torque in pound-feet and converting it to horsepower. Even at the rated peak power RPM you won’t really get the rated horsepower because a percentage is lost through auxiliary equipment on the engine and the process of getting it back to the wheels.
In a diesel engine the horsepower peaks at a lower RPM, and there is more torque at a lower RPM compared to a gasoline engine. This results in a diesel engine having much more power at a lower RPM, around the RPM range you will be towing at. This higher torque and higher horsepower at a lower RPM equates to better towing.
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